Gas chromatography and mass spectroscopy techniques for the detection of chemical contaminants and residues in foods

2 Gas chromatography and mass spectroscopy techniques for the detection of chemical contaminants and residues in foods P. Vazquez-Roig and Y. Pico, University of Valencia, Spain

Abstract: Gas chromatography-mass spectrometry (GC-MS) is an important technique for qualitative and quantitative analysis of food contaminants and residues. It is fast and sensitive, provides a high peak capacity and allows determination of thermally stable and volatile compounds. Recent research has resulted in better chromatographic columns and methods for sample preparation that enable a significant expansion of the application range of GC-MS, profiling strategies for sample characterisation being identified as important future drivers. Newer detection/separation solutions, such as fast chromatography, GC×GC, triple quadrupole mass spectrometry and time-of-flight mass spectrometry, are critically evaluated. The principles, recent developments and future perspectives of these new approaches to the determination of food contaminants and residues are discussed and examples of applications are shown. Key words: GC×GC, fast GC, time-of-flight, triple quadrupole, ion trap, applications, application range, future developments.

2.1

Introduction

Chromatographic separation methods are without any doubt the most frequently employed analytical techniques for determining food contaminants and residues (Menotta et al. 2010). Both gas chromatography (GC) and liquid chromatography (LC) are widely used in this field. LC and GC present a duality and could be at the same time complementary and competing techniques. Table 2.1 outlines the most applied chromatographic techniques for determining food contaminants and residues. As can be observed, there are a significant number of applications that can equally well be solved by GC as by LC (Baer et al. 2010; Paseiro-Cerrato

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et al. 2010; LeDoux 2011). For other applications, one of the techniques is clearly to be preferred over the other (Alder et al. 2006; Le Bizec et al. 2009; Baer et al. 2010; Malik et al. 2010). Which technique to select depends on numerous objective parameters, such as the physico-chemical properties of the analytes, matrix properties, the presence of similar analytes, the required sensitivity and selectivity, and so forth, as well as more subjective personal preferences (Alder et al. 2006; Pico and Barcelo 2008). In practice, the process of selecting between LC and GC is a process of multi-criteria decision-making in which incomparable properties have to be compared. Table 2.1 Common classes of chemical contaminants and residues in food and analytical techniques used for their determination Chemical contaminants in food

Analytical techniques

References

Agrochemicals Pesticide residues (e.g. herbicides, insecticides and fungicides)

GC-MS, GC-MS2, LC-MS, LC-MS2

De Pauw and MaghuinRogister 2006; Beyer and Biziuk 2008a; 2008b; Gilbert-Lopez et al. 2009; GonzálezRodríguez et al. 2009; Vidal et al. 2009; Baer et al. 2010; Sharma et al. 2010; LeDoux 2011

Pharmaceuticals Pharmaceutical and veterinary drug residues

LC-MS, LC-MS2, GC-MS

Le Bizec et al. 2009; Parr et al. 2009; Baer et al. 2010

Environmental contaminants Industrial chemicals and by-products Polychlorinated biphenyls GC-HRMS, GC-MS, GC-MS2, (PCBs) GC×GC-MS Brominated flame GC-MS, GC-MS2, LC-MS retardants (BFRs) Perfluorinated compounds GC-MS, LC-MS, LC-MS2 (PFCs) Polychlorinated dibenzo-p- GC-HRMS, GC-MS2, GC×GC dioxins/furans (PCDD/Fs) Polycyclic aromatic GC-MS, LC-FLD hydrocarbons (PAHs) Contaminants in food processing Heating Acrylamide GC-MS, LC-MS2 Chloropropanols

GC-MS, GC-MS/MS

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Beyer and Biziuk 2008a; 2008b Vonderheide 2009 Malik et al. 2010 De Pauw and MaghuinRogister 2006 Plaza-Bolaños et al. 2010

Wenzl et al. 2007; Keramat et al. 2011 Crews 2010

Gas chromatography and mass spectroscopy techniques Table 2.1

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Continued.

Chemical contaminants in food

Analytical techniques

References

Furan

GC-MS, GC-MS/MS

N-nitrosamines

GC-MS

Wenzl et al. 2007; León et al. 2008 Roberts et al. 2008; Vranova and Ciesarova 2009

Fermentation Ethyl carbamates

GC-MS

Materials in contact with food Melamine LC-UV, LC-MS2, GC-MS Phthalates GC-MS Bisphenols LC-MS, GC-MS, LC-FLD, LC-ED Natural toxins Mycotoxins LC-FLD, LC-MS

Weber and Sharypov 2009 Tyan et al. 2009 Cao 2010 Ballesteros-Gomez et al. 2009 Santini et al. 2009; Koppen et al. 2010; Li et al. 2011b

Notes: FLD, fluorescence detector; GC, gas chromatography; GC×GC, comprehensive twodimensional gas chromatography; GC-HRMS, chromatography-high resolution mass spectrometry; GC-MS, gas chromatography-mass spectrometry; LC, liquid chromatography; LC-ED and MS, liquid chromatography-electrochemical detector; LC-FL, liquid chromatography-fluorimetry; MS, mass spectrometry; MS2, tandem mass spectrometry; UV, ultraviolet detector; HR, high resolution; ED, electrochemical detector.

The general consensus when comparing LC and GC is that GC is faster, provides higher separation efficiency and has better properties for combination with mass spectrometric identification. The main question that determines whether a compound can be eluted from a GC column is whether or not it can reach a sufficiently high concentration in the gas phase in the GC column at a realistic temperature (Davies 2000; Baer et al. 2010). Virtually the only requirement for analytes is that they should be volatile or semi-volatile and thermally stable. Due to strong intermolecular forces, high temperatures are needed to vaporise polar molecules, which might decompose on the GC column. It is for this reason that small but highly polar molecules, such as quaternary ammonium salts and perfluorinated compounds, cannot be analysed using GC. A possible solution is the use of chemical derivatisation techniques whereby the polar groups of the target molecules are converted into less polar moieties, which favourably affects the vapour pressure and the adsorption characteristics (Fialkov et al. 2007). The drawback of derivatisation reactions is that they are time-consuming, intensive and tedious (Hoh et al. 2008). However, unquestionably, GC is still one of the answers to screening, identifying and quantifying many groups of moderately polar and non-polar food contaminants and residues (Fialkov et al. 2007; Hoh et al. 2008).

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After its invention in 1952, GC expanded with great rapidity over the following two decades, and much current practice has its roots in that period (Baer et al. 2010). The introduction of robust, efficient and reproducible fused-silica capillary columns and the provision of relatively inexpensive but reliable equipment for GC-MS provided a crucial new impetus in the 1980s. Since then, the versatility of GC has expanded its application areas. In particular, chromatography had, and still has, a vital role to play in food contaminants and residue analysis (Lehotay and Hajslova 2002). In this chapter, we will review the recent innovations in the area of GC applied to food contaminants and residue analysis because, even though GC already qualifies as a robust technique, it is taking impressive new strides toward speed-up of analyses, fast separations, two-dimensional separations, automated sample handling, and the integration of high-performance computational power within gas chromatographic platforms. Together with the better quality of columns and the wider choice available, researchers are pushing forward new applications. The principles of the generic options and different modes of operation shown in Fig. 2.1 will be discussed, and examples of how researchers have successfully applied the particular approaches to food contaminants and residue analysis will be shown. 2.1.1

Extraction: main techniques and importance prior to gas chromatography (GC) analysis The sample preparation before GC analysis is important. Many different sample pre-treatment methods have been proposed for the extraction of pesticide residues

Fig. 2.1

Different GC-MS operation modes.

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from food samples, the most common of which has been blending with an organic solvent such as acetone, ethyl acetate or acetonitrile. The Quick, Easy, Cheap, Effective, Rugged, Safe (QuEChERS) method deserves special mention because it is widely used in food safety. The method is based on a single-step acetonitrile extraction and salting out by liquid–liquid partitioning from the water in the sample with MgSO4 followed by dispersive solid-phase extraction (SPE) (Prestes et al. 2009; Baer et al. 2010; Koesukwiwat et al. 2010a; 2010b; Lehotay et al. 2010a; 2010b; 2010c; Mastovska et al. 2010). So far, promising results have been achieved by LC or GC analysis, including pesticides as well as acrylamide, polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals and veterinary drugs (Baer et al. 2010; Chen et al. 2010; Kolberg et al. 2011). Other techniques such as supercritical fluid extraction (SFE), pressurised-liquid extraction (PLE), microwave-assisted extraction (MAE), matrix solid-phase dispersion (MSPD), solid-phase extraction (SPE), liquid-phase microextraction (LPME), solid-phase microextraction (SPME) and stir-bar sorptive extraction (SBSE) have also been reported (Hernandez et al. 2007; Lambropoulou et al. 2007; Hakkarainen 2008; Lancas et al. 2009; Baer et al. 2010; Garcia-Rodriguez et al. 2010; Pakade and Tewary 2010; Prieto et al. 2010). Current trends in extraction include simplification of sample preparation, adoption of environmentally friendly methods, and automation or on-line coupling of the analytical procedure (Baer et al. 2010; Prieto et al. 2010). Within this trend, pressurised hot water extraction (PHWE) has become a popular ‘green’ extraction method for different classes of compounds present in numerous kinds of food (Teo et al. 2010). There have been many sample preparation techniques proposed to meet the requirements connected with the multiplicity of foods. Optimal sample preparation can reduce analysis time and sources of error, enhance sensitivity and enable unequivocal identification and quantification. Several reviews considering all aspects of sample preparation, ranging from general extraction techniques to more selective techniques for determining organic contaminants in food, show that GC is compatible with almost all extraction techniques (Ridgway et al. 2007; Beyer and Biziuk 2008b; Sandra et al. 2008; Baer et al. 2010; Fussell et al. 2010; Tadeo et al. 2010; Teo et al. 2010). Some practical problems still need to be resolved; for example, traditional sample preparation techniques are time-consuming and require large amounts of solvents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. The complete removal of all matrix components is clearly unrealistic. Non-volatile co-isolated matrix components such as lipids, pigments and other higher molecular weight components can provoke various problems of a more fundamental nature and more complicated to solve, such as the matrix effect. Co-injected matrix components tend to block active sites in the GC system (mainly free silanol groups), reducing analyte losses and thus enhancing the analyte signal. In these cases, quantitative use of data requires (i) elimination of the primary causes, (ii) optimisation of calibration strategy enabling compensation and (iii) optimisation of injection and separation parameters. Even with the emergence of advanced techniques such as mass spectrometry, complex matrices, such as food, require extensive sample extraction and purification.

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2.2

Gas chromatography injection techniques

2.2.1 Conventional injection techniques The great analytical strength of capillary GC lies in its high resolution. The average capillary column (30 m long) has approximately 100 000 theoretical plates. However, with this separation power comes some limitations, because capillary columns have diameters from 0.05 to 0.53 mm and require relatively specialised injectors with ancillary flow, pressure controllers and a small amount of sample. The success of GC chromatography depends to a great extent on the injection technique, in order to obtain sharp, well-resolved peaks. The conventional injection techniques are:

• • •

Split/splitless. On-column injection. Programmed temperature vaporisation injection (PTV).

The injection of 20–100 μl liquid volume, rather than the formerly standard 1–2 μl, is now routinely possible, by using sample introduction systems such as on-column and PTV. A 100 μl injection will easily allow measurement of solute concentrations of 100 ppt. Both split and splitless injection modes utilise the same instrumentation, but working in two different ways. In split mode, most of the sample injection will pass out through the split vent to the atmosphere and only a small proportion (ca. 1%) will flow into the column. This technique is not suitable for trace analysis where very low detection limits are required. On the contrary, the conventional splitless injection allows most of the analyte in the injected extract to be introduced into the column by simply closing the split valve. The splitless mode in its different variants is widely used in food residues analysis because it achieves high and narrow peaks (de Carvalho et al. 2009). This approach has been applied to determine organochlorine pesticides (OCPs) (Hiebl and Vetter 2007; Marti-Cid et al. 2008b; Blanes et al. 2009; Baer et al. 2010), PAHs (Marti-Cid et al. 2008a; Baer et al. 2010), polychlorinated biphenyls (PCBs) (Bolanos et al. 2007; Adenugba et al. 2008; Baer et al. 2010), polybrominated diphenyl ethers (PBDEs) (Chen et al. 2010), dibenzo-p-dioxinas policloradas y dibenzofuranos policlorados (PCDD/Fs) (Baer et al. 2010), pesticides (Blanes et al. 2009; de Carvalho et al. 2009; Kolberg et al. 2011), 3-monochloropropane-1,2-diol (3-MCPD) (Zelinkova et al. 2008), tropane alkaloids (Caligiani et al. 2011) and phthalate esters (Walorczyk 2008). The disadvantage of splitless injection is that it requires more time for method development than split mode, and its advantages are that the sample spends more time in the injector, volatilising more slowly, and thus the injector can work at a lower temperature than in split injection mode. It reduces the possibility of thermal degradation of some analytes and the occurrence of tailing peaks, caused by a rapid vaporisation of the sample. Lower temperatures can improve chromatogram resolution too. However, the classical splitless injection enables only 1–2 μl of a liquid to enter the capillary column. In some cases, this injection can be increased up to 5–10 μl using a pressure pulse during the sample introduction process (Kim et al. 2010).

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In cold on-column injection, small sample volumes (up to 1–2 μl) are directly introduced by a special syringe onto the analytical column or a retention gap at lower temperature (e.g. 60–80°C). The entire sample enters the column, which removes the possibility of decomposition into the inlet chamber. But, as a consequence of this, an extensive sample clean-up is necessary in order to avoid matrix interferences. This low-temperature injection eliminates both syringe needle and inlet discrimination and might be suitable specifically for high-boiling analytes. On the other hand, the introduction of the entire sample, including both analytes and interferences, into the GC system is associated with increased demands for cleaning and maintenance when such complex samples as food are analysed (Lehotay and Hajslova 2002; Hajslova and Cajka 2007). On-column injectors are rarely used nowadays. The PTV injector represents the most versatile GC inlet, offering mitigation of most problems encountered when using a hot vaporising device such as splitless and/or cool on-column injection in trace analysis. Regardless of whether PTV is operated in split or splitless mode, the important fact is that the injector chamber at the moment of injection is kept cool. A rapid temperature increase, following withdrawal of the syringe from the inlet, allows an efficient transfer of the volatile analytes onto the front part of the separation column while leaving behind nonvolatiles in the injection liner. In recent years, application of PTV injection has been demonstrated to be successful in the analysis of food contaminants and residues (e.g. PCBs (Walorczyk 2008), pesticides (Ahire et al. 2008; Cajka et al. 2008; Stajnbaher and Zupancic-Kralj 2008; Gonzalez-Rodriguez et al. 2009; 2011; Cus et al. 2010), PAHs (Gomez-Ruiz et al. 2009), melamine (Tzing and Ding 2010) and cyanuric acid (Tzing and Ding 2010)). This injector is ideally suited to thermally labile analytes and samples with a wide boiling range (when needed, PTV temperature can be programmed higher than the usual column temperature, allowing injection of analytes that would not pass through the classic split/splitless inlet). It allows introduction of large sample volumes, up to hundreds of microlitres, into the GC system, either all at once or over a period of time. No retention gaps or pre-columns are needed for this purpose; instead, the liner size is increased. This feature makes PTV particularly suitable for trace analysis and also enables it to be coupled on-line with various enrichment and/or clean-up techniques, such as automated SPE approaches. 2.2.2 Large volume injection techniques Large volume injection (LVI) has become a fundamental prerequisite of modern GC analysis, especially when trace components, such as food contaminants and residues, have to be determined at very low levels. For the injection of large volumes, up to hundreds of microlitres of sample, on-column and PTV injection techniques have been mainly used (and/or modified) (Hoh and Mastovska 2008; Hyötyläinen 2008; Baer et al. 2010). The most critical problem in LVI is a huge solvent vapour volume resulting from the expansion of the large liquid volume of the injected solvent. On-column injection solved this problem using a retention

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gap, which provides room for the large injected solvent volume to condense and expand (Blanes et al. 2009). It has been used for a wide range of analytes, from very volatile, such as aroma compounds, to semi-volatile, including, for example, PCBs. However, in the last decade, on-column LVI has been falling into disuse. The PTV injection separates solvent vapour from analytes through venting of the vapour in the liner. Compared with the original design, installation of a solvent vapour exit (SVE) and its electronic flow meter enables on-column LVI to be used practically. Availability of different packing materials and liners, and systematic PTV parameter optimisation, broaden the scope of PTV LVI applications. The PTV LVI for GC-MS has been scrutinised to determine PAH in meat products (de Carvalho et al. 2009), volatile compounds in wines (Coelho et al. 2008), and pesticide residues in fruits, vegetables and seaweeds (Stajnbaher and ZupancicKralj 2008; Barriada-Pereira et al. 2010; Garcia-Rodriguez et al. 2010). Compared with PTV injection in splitless mode, the PTV solvent vent injection method provided an enhancement of sensitivity for all target PAHs. Especially significant was the improvement of the signel-to-noise (S/N) ratios of the compounds with the highest molecular mass (de Carvalho et al. 2009). On-column LVI is superior for highly volatile and thermally labile compounds, whereas PTV LVI is beneficial in the analysis of dirty matrix samples. New LVI techniques developed during the past decade, such as modified PTV techniques (direct sample introduction/difficult matrix induction (DSI/DMI) and through oven transfer absorption/desorption (TOTAD)) and overflow techniques (splitless overflow and at-column) are promising. Those based on modified PTV techniques have been used in some interesting applications. On the contrary, the applications of the overflow techniques are rather limited. In the DSI/DMI LVI, the sample (solid or liquid) is placed in a disposable microvial, which is introduced into a PTV injection port. This technique has been mainly used in the analysis of pesticide residues in various food matrices (Hoh et al. 2008; 2009a; 2009b; Mastovska et al. 2010), demonstrating the robustness of the DSI/DMI device for dirty matrix samples (e.g. cereals (Mastovska et al. 2010) and fish oils (Hoh et al. 2009a; 2009b)). One interesting application of DSI/DMI in fish oil analysis is the simultaneous determination of PCBs, OCPs and PBDEs (Hoh et al. 2009b). Figure 2.2 shows a comparison of responses of selected PCBs and PBDEs in cod liver oil of different sample sizes (0.1, 0.25, 0.5 and 1 g) after gel permeation chromotography (GPC) clean-up by injection using microvials in DSI. In addition to this application still being highly relevant, it is also interesting to see the main problems these authors were faced with, which are still a nuisance today: the peak responses of the less volatile compounds remained fairly constant when the sample size increased because more lipids remained in the final extracts as sample size in GPC increased, which caused worse transfer efficiency of the heavier compounds from the DSI microvial to the GC column. The TOTAD interface allows the introduction of several millilitres of water, while maintaining good chromatographic characteristics. The water is almost entirely eliminated, so that LVI of aqueous samples and an MS detector can be used without problems (Toledano et al. 2010). TOTAD has been proposed to

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Fig. 2.2 Comparison of responses of PCB and PBDE congeners in cod liver oil of different sample sizes (0.1, 0.25, 0.5 and 1 g) cleaned up once by GPC and injected using microvials in DSI. (a) The responses are normalised to the 0.1 g results. (b) The peak responses are normalised to internal standards (INST) in each sample and then are normalised to the 0.1 g results. For direct proportionality, the individual bars should reach 1, 2.5, 5 and 10 on the y-axis for the 0.1, 0.25, 0.5 and 1 g responses, respectively. (Reproduced from Hoh et al. 2009b with permission of the American Chemical Society.)

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determine pesticides in lycopene and other carotenoid extracts by RPLC–GC (RPLC, reversed phase liquid chromatography) (Cortes et al. 2009). Further applications of this promising interface for LVI are expected in the near future. 2.2.3 On-line coupling of extraction/injection There are two ways to couple on-line extraction and GC-MS. The analytes isolated by sorptive extraction methods (such as SPME, SBSE or in-tube SPME) can be directly desorbed into the GC system by thermal desorption. This simplified sample preparation makes routine analysis of a large number of samples fast and easy. Some applications use headspace (HS)-SPME (e.g. furan determination in selected food samples (Altaki et al. 2009), 2-phenoxyethanol (ethylene glycol monophenyl ether, C8H10O2) in fish (Klimankova et al. 2008), bisphenol A (BPA) and bisphenol F (BPF) in canned food (Goicoechea et al. 2008) and ethanol in cooked meals containing alcoholic drinks (Mateus et al. 2011)). In the case of furan, HS-SPME-GC-ITMS (ITMS: ion trap mass spectrometry), compared with the automated headspace-GC-MS method, proposed by the US Food and Drugs Administration (US FDA), provided better precision relative standard deviation (RSD), 9–12%) and lower limits of detection (from 5 to 20 times lower) (Altaki et al. 2009). Rastkari et al. (2010) investigated the feasibility of single wall carbon nanotubes (SWCNTs) as a HS-SPME adsorbent for the determination of bisphenol derivatives in canned food. For both target analytes, the limit of detection (LOD) was 0.10 μg/kg. This study also compares the SWCNT and a commercial polydimethylsiloxane (PDMS) SPME fibre. SWCNT fibre showed higher extraction capacity, better thermal stability (over 350°C) and longer lifespan (over 150 times) than the commercial PDMS fibre. Although the direct application of SPME to complex liquid food samples can be difficult because of proteins, sugars and so on, in the literature there are some examples of the direct use of SPME with aqueous samples, such as determination of furan levels in various canned and jarred foods (Kim et al. 2010) and baby food (Arisseto et al. 2010) and of tetramethylene disulfotetramine in foods. The latter study presents a comparison of direct immersion (DI) and HS extraction techniques using a 70 μm carbowax/divinylbenzene (CW/DVB) fibre (De Jager et al. 2008). The optimised DI-SPME method provided an aqueous extraction LOD of 9.0 ng/g, while the HS-SPME LOD (limit-of detection) was 2.7 ng/g. In both SPME modes, recovery was highly matrix-dependent, and quantification required standard addition calibrations. Analysis of foods using DI-SPME encountered many obstacles, including fibre fouling, low recovery and poor reproducibility, while HS-SPME was successfully applied to food analysis with minimal interferences. The interferences and difficulties detected in DI-SPME could be solved by incorporating the fibre inside a hollow cellulose membrane, as demonstrated by Li et al. (2011a) for the simultaneous determination of 25 pesticides of different chemical classes which were spiked into fresh grape. The validation of the optimised method showed that the proposed procedure is sensitive (the limits of detection were in the range of 0.9–8.4 ng/ml for 25 pesticides), precise and

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repeatable (average recoveries were between 61% and 108% with relative standard deviations from 4.0% to 12.4%). Alternatively, a miniaturised liquidphase extraction procedure based on directly suspended droplet microextraction (SDM) was also coupled on-line with GC-MS (Viñas et al. 2011). Another way to couple extraction and determination directly is the automated introduction of the extract on-line in LVI without a pre-concentration step. Also, coupling of LC and GC is a very powerful system for substantial time-saving in sample preparation and better reproducibility. The LC offers high sample capacity and a wide range of separation mechanisms, so it can be utilised in selective clean-up. The GC provides high separation efficiency and a variety of detection methods. In addition, the closed system reduces error potentially occurring in offline sample preparation. To transfer the liquid fractions to the GC system on-line, a high-capacity LVI is required. Recent studies proposed the use of SBSE-LD/ LVI-GC-MS (SIM) for the determination of several food contaminants and residues (e.g. 20 OCPs in lettuce, spinach, green bean, green pepper, tomato, broccoli, potato, carrot and onion (Barriada-Pereira et al. 2010) and volatiles in wines (Coelho et al. 2008)). A recently developed TOTAD injector has a large capacity for polar solvents and has been successfully adapted in on-line RPLC–GC (e.g. pesticides in carotenoid extracts; Cortes et al. 2009). Recent interest in comprehensive twodimensional LC×GC separations, in which all fractions eluting from LC are introduced into the GC system, will probably be a driving force in future developments in on-line RPLC–GC coupling.

2.3

Gas chromatography separation strategies

2.3.1 Conventional GC Conventional GC-MS provides relatively high-efficiency separations, depending on the carrier gas, oven temperature and column characteristics. Capillary columns are a thin fused-silica (purified silicate glass) capillary (typically 10–100 m in length and 250 μm inner diameter) that have the stationary phase coated on the inner surface. The polarity of the analyte is crucial for the choice of stationary compound, which in an optimal case would have a similar polarity to the solute. Common stationary phases in open tubular columns are cyanopropylphenyl dimethyl polysiloxane, carbowax polyethyleneglycol, biscyanopropyl cyanopropylphenyl polysiloxane and diphenyl dimethyl polysiloxane. These conventional GC-MS columns have been applied to food analysis for the determination of cyanuric acid and melamine (Tzing and Ding 2010), furan (Roberts et al. 2008; Altaki et al. 2009; Arisseto and Ding 2010; Guenther et al. 2010; Kim et al. 2010; Ruiz et al. 2010), bisphenols (Goicoechea et al. 2008), pesticides (Aysal et al. 2007; Adenugba et al. 2008; Garrido Frenich et al. 2008; Stajnbaher and Zupancic-Kralj 2008; Fuentes et al. 2009; Gonzalez-Rodriguez et al. 2009; 2010; 2011; Mawussi et al. 2009; Mezcua et al. 2009; Kmellar et al. 2010; Koesukwiwat et al. 2010a; Lehotay et al. 2010c; Kolberg et al. 2011; Li et al. 2011a), phthalates (Del Carlo et al. 2008;

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Gartner et al. 2009), 2-phenoxyethanol (Klimankova et al. 2008), ethanol (Mateus et al. 2011), PBDE (Hiebl and Vetter 2007; Chen et al. 2010), tetramethylene disulfotetramine (De Jager et al. 2008), 3-monochloropropane-1,2-diol (3-MCPD) (Canterino et al. 2008; León et al. 2008; Baer et al. 2010), tropane alkaloids (Caligiani et al. 2011), PCBs (Bolanos et al. 2007; Morrissey et al. 2007; Serrano et al. 2008a; 2008b), hexachlorobenzene (HCB) (Marti-Cid et al. 2008b), PCDD/ Fs and dioxin-like PCBs (Menotta et al. 2010) and PAH (Marti-Cid et al. 2008a; Kuhn et al. 2009; Wretling et al. 2010). 2.3.2 Fast GC GC is a popular and powerful analytical tool, but often suffers from long analysis times. Speed of analysis is important to many of today’s GC analysts as they look for ways to improve sample throughput. Without sacrificing the quality of the analysis, there is little that is more valuable than sample throughput. The primary aim of fast GC is to maintain (compared with conventional GC) sufficient resolving power in a shorter time. Fast GC uses column and instrument improvements in combination with optimised run conditions to provide analysis times three to ten times faster, while still providing acceptable resolution. Fast GC can be accomplished by manipulating a number of the analysis parameters, such as column length, column internal diameter (ID), stationary phase, film thickness, carrier gas, linear velocity, oven temperature and ramp rate. Fast GC is typically performed using short, 0.10 mm or 0.18 mm ID capillary columns with hydrogen carrier gas and rapid oven temperature ramp rates. Based solely on column internal diameter (ID), capillary GC can be grouped into three types:

• • •

Conventional GC: 0.25 mm ID columns (megabore, wide bores and narrowbore columns). Fast GC: 0.10 to 0.18 mm ID columns (can be performed on most conventional GCs). Microbore columns – Ultra-Fast GC: 0.050 mm ID columns (may require a special GC); sub-microbore columns.

Megabore, wide-bore and narrow-bore columns provide several benefits as compared with microbore columns, such as higher sample capacity, improved ruggedness and fewer instrumentation problems (Donato et al. 2007). When connected to MS as a source of vacuum, short megabore columns can be operated at lower pressures along the entire column length, i.e. low pressure GC (LP-GC) (Ravindra et al. 2008). Lower column pressures lead to a higher diffusivity of the solute in the gas phase, resulting in faster separation as compared with the use of the same column operated at atmospheric outlet pressure conditions. The direct connection of a short megabore column to the MS also requires sub-atmospheric pressure conditions at the injector. The simplest way to achieve this is to employ a short, narrow restriction capillary connected to the front of a wider analytical column. Fast GC has acquired real importance in pesticide residue analysis. Dromonova and Maskova provided an overview of fast GC methods for analysis

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of pesticide residues in a variety of matrices at ultra-trace concentration levels (Domotorova and Matisova 2008). In the past few years, LP-GC has been applied to the fast analysis of various pollutants in different food matrices (e.g. multiple pesticide residues in fruit-based baby food (Cajka et al. 2008) and grapes, must and wines (Cunha et al. 2009)). A drawback of LP-GC is its lower chromatographic resolution compared with the conventional GC approach. Although the MS can compensate in many cases, the potential co-elution of isomeric compounds can occur. Figure 2.3 shows separation of selected isomeric compounds in LP-GC using a short megabore column and conventional GC employing a standard narrow-bore column. The chromatographic resolution of two closely eluted isomers of HCH (i.e. β-HCH and γ-HCH) reached a resolution of 4.6 in conventional GC compared with 1.2 in LP-GC. The isomeric pair p,p′-DDD and o,p′-DDT represented compounds with a low resolution even in conventional GC (0.96) and in the case of LP-GC analysis co-elution of these two compounds occurred (Cajka et al. 2008). Similarly, the two isomers of difenoconazole, with a resolution of 1.3 in conventional GC, were almost fully co-eluted in LP-GC (R = 0.3). Although the use of LP-GC results in a loss of separation efficiency, it offers a threefold to fivefold reduction in analysis time for organic compounds, thus increased sample throughput, and enhancement of the signal-to-noise ratio, leading to improved detection limits. 2.3.3 Two-dimensional GC Comprehensive two-dimensional gas chromatography (GC×GC) was developed in 1991 by Phillips, and it consists of two columns connected serially such that all sample portions emerging from the first instrumental method enter the second and are analysed sequentially. The hyphenation produces two-dimensional data in which each instrument supplies an axis. The only instrumental difference between the designs of GC×GC and GC-MS is the use of another column rather than a mass analyser in the second dimension. In both cases, sample portions eluting from a GC column are fed into a second separation device. GC-MS uses a mass analyser as the second separation device to produce a series of mass spectra from the eluted sample portions. GC×GC uses another GC column as the second separation device to produce a series of chromatograms from the sample portions eluted from the first column. High-end GC×GC systems use the two-dimensional separation steps (the first dimension is a non-polar GC column; a short, fast, polar GC column is used in the second dimension) in combination with time-of-flight mass spectrometry (TOF(MS)) as a third dimension. These systems are used for the analysis of very complex samples such as oils and environmental and food samples. GC×GC-TOF(MS) is also an important analytical tool in the field of food contaminants and residues. The main developments and applications of multidimensional chromatographic techniques in food analysis were reviewed by Chen et al. (2010), who examined different aspects related to the existing couplings involving chromatographic techniques (e.g. multidimensional GC,

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© Woodhead Publishing Limited, 2012

Fig. 2.3 GC separation of HCH-isomers (m/z 180.938), DDD- and DDT-isomers (m/z 235.008), and difenoconazole-isomers (m/z 323.024) at a concentration of 0.05 mg/kg under the conditions of (a) LP-GC (3 m × 0.15 mm restriction capillary coupled to 10 m × 0.53 mm, 0.5 μm Rtx-5 Sil MS column), and (b) conventional GC (30 m × 0.25 mm, 0.25 μm Rtx-5 Sil MS column). A mass window of 0.02 Da used in the experiment. (Reproduced from Cajka et al. 2008 with permission of Elsevier.)

Gas chromatography and mass spectroscopy techniques

31

multidimensional LC and multidimensional supercritical fluid chromatography (SFC), as well as all their possible combinations). This technique has been applied to the determination of more than 100 pesticide residues (van der Lee et al. 2008), 52 benzenic and halogenated volatile organic compounds in animal-derived products (Ratel and Engel 2009), organochlorine (Hoh et al. 2008; 2009b), PCBs [190, 191, 193, 196], smaller organohalogen compounds (Hoh et al. 2009b), PBDE (Hoh et al. 2009b), brominated hydrogenated natural products (HNPs) (Hoh et al. 2007; 2008; 2009a; 2009b) et al. 2009b), dioxins (Hoh et al. 2007; 2008) and furans (Hoh et al. 2007; 2008) in fish oil. The fitting of the columns was by cryogenic modulation and the detection by TOF-MS. This technique is extremely powerful for analysis of dioxins and other less conventional food contaminants and residues. As an example of the separation power of this technique, Ratel and Engel (2009) evaluated the capability of the use of GC×GC by comparing results using one-dimensional GC-MS and GC×GC-TOF/MS, observing a spectacular increase in the number of benzenic compounds detected, from 11 to 69 for lamb fat, from seven to 58 for oyster flesh and from five to 66 for cow milk, while the number of halogenated compounds increased from none to 12 for lamb fat, from four to 25 for oyster flesh and from two to 22 for cow milk. These results show the need for a correct separation of co-eluting analytes for a correct estimation of the contamination levels of a sample. The performance of GC×GC-TOF/MS for comprehensively detecting benzenic and halogenated volatile organic compounds (BHVOCs) and showing their entryways in animal-derived food chains was assessed. Meat, milk and oysters were analysed by GC-Quad/MS and GC×GC-TOF/MS. For all these products, at least a sevenfold increase in the contaminants detected was achieved with the GC×GC-TOF/MS technique (Ratel and Engel 2009). Furthermore, van der Lee et al. (2008) applied GC×GC–TOF-MS for qualitative and quantitative determination of pesticide residues and contaminants in animal feed (a very complex matrix). GC×GC can separate an order of magnitude more compounds than conventional gas chromatography without the requirement for time-consuming sample preparation techniques, and its key advantages are increased peak capacity, increased resolution and increased detectability: all highly desirable for simultaneous trace levels and identification in complex matrices.

2.4

Gas chromatography-mass spectrometry detection

2.4.1 Ionisation techniques The standard ionisation technique in GC-MS is electron impact ionisation (EI) with electrons of 70 eV kinetic energy. EI is a universal ionisation method, since all organic compounds are ionised with a comparable efficiency. Organic compounds are usually heavily fragmented by the ionisation process. The resulting fragmentation ion pattern in the mass spectrum represents a more or less specific fingerprint of the analysed molecule. Thus compounds can often be identified using mass spectrometric libraries. Ideally the mass spectrum of a (separated) compound contains the molecular mass peak as well as several characteristic

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Chemical contaminants and residues in food

fragment peaks. However, in many cases the interpretation is hampered because the molecule is too fragile and does not exhibit a molecular mass peak and/or the fragment pattern is not specific. To solve this problem, other soft and selective ionisation methods can be applied. Selective ionisation methods only ionise compounds with specific chemical or physical properties and typically show little or no fragmentation (soft ionisation). The most common soft and selective ionisation method for gaseous compounds is chemical ionisation, in which the analyte molecules are ionised by chemical ion–molecule reactions. Chemical ionisation has been used in negative mode to determine pesticides (Kolberg et al. 2011). 2.4.2 Mass analysers Table 2.2 shows a summary of the most important characteristics of the mass spectrometers used in food contaminants and residue analysis. Mass spectrometry is the most commonly applied spectrometric detection method for GC (GC-MS). Often quadrupole (QMS) or ITMS mass spectrometers are used for this purpose. Typically, MS is employed for detection of target compounds. The use of GC-MS allows the identification and quantification of a wide range of even trace amounts of GC-amenable food contaminants and residues in complex matrices. Currently, low-resolution (unit mass) MS detectors employing either single quadrupole or ion trap analysers are most routinely used in applications. As powerful as MS is, the low-resolution, scanning MS systems have limits in data collection rate, avoidance of interferences, and spectral information provided for identification purposes. As an example of the potential of GC-MS to identify compounds, during routine gas chromatography with electron capture detection (GC/ECD) analysis of chicken eggs, Hiebl and Vetter (2007) observed that the most prominent peak in some samples did not match the retention time of any of the food contaminants screened. Subsequent GC-MS studies clarified that the mass spectrum of the peak was very similar to hexabromocyclododecane (HBCD), which was also identified in the egg by GC-MS. The unknown compound was positively identified as pentabromocyclododecene (PBCDE), a metabolite of HBCD detected for the first time in foodstuffs. GC-MS determination indicated five bromine substituents on PBCDE (Fig. 2.4). However, GC-MS does not allow clarification of whether the detected peak represents one or a mixture of more than one PBCDE. For complex samples, even highly resolved capillary gas chromatograms can often achieve only a limited separation of the analytes. Ultra-complex samples, such as PCBs or dioxin in food extracts, thus typically exhibit regions where multiple overlapping eluent peaks form broad congested areas in the chromatogram (UCM, unresolved complex mixture). An improved analysis of such highly complex mixtures can be achieved by further increasing the selectivity of hyphenated instrumental analytical technologies. In general, two strategies are possible to increase the selectivity of hyphenated analytical methods: (i) enhancement of the separation power of the chromatographic technique (GC×GC, see previous section) and (ii) improvement of the selectivity of spectrometric detection technology.

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Table 2.2

General specifications and features of currently available mass analysers Mass range (Da)

Mass Spectral Acquisition accuracy acquisition mode speeda 15 Hz

Sensitivity Linear dynamic range

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q

<1050

QqQ

<1500

IT

<1000

0.1–0.2 (Da)

5 Hz

DF <4000 magnetic sector High-speed <1000 TOF High<1500 resolution TOF

<5 ppm

7 Hz

pg in full scan fg in SIM pg in full scan pg in MS/ MS Full scan, SIM, pg in full full scan of scan product ions Full scan, SIM fg in SIM

500 Hz

Full spectra

pg

20 Hz

Full spectra

fg–pg

<5 ppm

Full scan, SIM, simultaneous full scan/SIM Full scan, SIM, full scan of product ions

Versatility Mass resolution

Performance/ MS/MS cost

>5 orders of magnitude

EI, PCI, NCI

Unit mass

Low

None

>5 orders of magnitude

EI, PCI, NCI

Unit mass

High

MS2 (in space)

4–5 orders of EI, PCI, magnitude NCI

Unit mass

Low

>5 orders EI, PCI, of magnitude NCI EI

>10 000 Very high (10% valley definition) Unit mass High

MSn (in time), n = 2–10 Only with special configuration None

EI, PCI, NCI

>7000 (FWHM)

4 orders of magnitude 4 orders of magnitude

High

None

Notes: DF, double focusing; EI, electron ionisation; FWHM, full width at half maximum; IT, ion trap; NCI, negative chemical ionisation; PCI, positive chemical ionisation; q, quadrupole; qQq, triple quadrupole; SIM, selected reaction monitoring; TOF, time of flight. a

m/z 50–500 Da

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Fig. 2.4 GC/EI-MS of PBCDE with one possible general structure inserted. Masses in parentheses are the assigned monoisotopic peak, which was not detected because of low isotope abundance. (Reproduced from Hiebl and Vetter 2007 with permission of the American Chemical Society.)

Gas chromatography and mass spectroscopy techniques

35

TOF-MS has been applied to both strategies through two complementary approaches: (i) instruments that feature unit mass resolution at high acquisition speed (up to 500 spectra/s), which predetermines their use as detectors coupled to fast and ultra-fast GC or comprehensive two-dimensional GC (GC×GC); and (ii) instruments with a moderate acquisition speed (max. 20 spectra/s), but having high mass resolution (>7000 FWHM (full width at half maximum)), which allows a greater ability to resolve the analytes from the matrix components. Additionally, mass measurement accuracy (<5 ppm) permits estimation of the elemental composition of the detected ions. Particularly valuable is the review by Cajka and Hajslova on the recent progress in instrumentation design that has led to the renaissance of TOF mass analysers for the determination of a wide range of both target and non-target organic components occurring in various biotic matrices (Cajka and Hajslova 2007). To illustrate the potential to identify unknown compounds with GC×GC coupled to high-speed TOF, Fig. 2.5 shows the chromatogram obtained after analysing salmon oil. Seven 1,1ʹ-dimethyl-2,2ʹ-bipyrroles (DMBPs) congeners are reported for the first time (Fig. 2.5). They were tentatively identified by the similarities of their mass spectra to other DMBP reference standards of other congeners (Hoh et al. 2009a). Mass spectrometers with high or ultra-high mass resolution, for example, allow the deduction of the elemental composition of the detected ions (i.e. via the exact mass numbers). GC coupled to high-resolution time-of-flight mass spectrometry (GC-HR-TOF-MS) is a powerful analytical technique with excellent capabilities due to its high sensitivity in full-spectrum-acquisition mode together with its resolving power and accurate mass measurements. These features make this technique very attractive in qualitative analysis, especially for wide-scope screening of a large number of organic contaminants and residues at trace levels. Full-spectrum MS allows data processing, in principle, of an unlimited number of compounds in samples, as no analyte-specific information is required before the injection. Also, as all data remain available, retrospective analysis is always possible without the need to re-inject the sample – an important advantage of fullspectrum MS techniques. Despite these advantages, GC-HR-TOF-MS has rarely been applied, so promising results can be expected in different applied fields in the years ahead. The characteristics and the potential of GC-HR-TOF-MS have recently been discussed in detail in an excellent review by Hernandez et al. (2011). Recent instrumental developments (e.g. high-speed analog-to-digital converter or soft ionisation sources) and advances in software for processing the huge amount of data available open up new prospects, making GC-TOF-MS one of the most promising techniques to investigate the presence of organic compounds in different fields (Chen et al. 2010). GC-HR-TOF-MS has been applied to analysis of multiple pesticide residues in fruit-based baby food (Cajka et al. 2008) and fruit and vegetables (Koesukwiwat et al. 2010b). As an example, Fig. 2.6 shows identification of the pesticide iprodione. Mass spectral deconvolution software provides an effective tool for automated resolution of co-eluting peaks. Peak location/detection and generation of ‘clean’ mass spectra assigned to co-eluting peaks, followed by search against commercially available libraries, are conducted.

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Chemical contaminants and residues in food

Fig. 2.5 GC×GC/ToF-MS chromatogram (2D plot) of m/z 386, 466, 500, 510, 544, 590, and 634 indicating DMBP congeners in salmon oil. x- and y-axes represent 1D and 2D retention times in seconds. * indicates newly detected DMBP congeners. EI mass spectra of peaks in the salmon oil potentially identified as (a) DMBP-H2Br2Cl2, (b) DMBPHBr3Cl2, and (c) DMBP-HBr4Cl. (Reproduced from Hoh et al. 2009a with permission of the American Chemical Society.)

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Gas chromatography and mass spectroscopy techniques

37

Fig. 2.6 Iprodione in buffered QuEChERS baby food extract at a level of 0.1 mg/kg. (a) Mass spectrum of elution area of iprodione without deconvolution; (b) deconvoluted mass spectrum of iprodione (library match with a reverse factor of 794); (c) NIST library mass spectrum of iprodione. (Reproduced from Cajka et al. 2008 with permission of Elsevier.)

This approach makes compound identification in GC-MS more convenient, more reliable and faster. Another possibility is the application of tandem mass spectrometry (MS/MS), in which mass selected ions of a (first) mass spectral analysis are again excited, fragmented and analysed in a further mass spectroscopic separation step. MS/MS can be conceived in two ways: tandem in space (e.g. triple quadrupole, QqQ) or in time (e.g. ion trap, IT). The IT methods allow positive results to be confirmed, but the running time is relatively high when multi-residue methods have to be

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Chemical contaminants and residues in food

developed, due to the lower scan speed of IT compared with QqQ. GC-QqQ-MS/ MS has been used for the simultaneous analysis of 57 compounds, including OCPs, OPPs and PCBs, at trace levels in eggs (Bolanos et al. 2007). Applications of the IT detector operated in MS/MS mode include the determination of 2-phenoxyethanol in anaesthetised fish (Klimankova et al. 2008), 3-MCPD in foodstuffs (León et al. 2008) and isophenphos methyl in peppers (Mezcua et al. 2009). Garrido Frenich et al. (2008) compared both tandem mass spectrometry analysers for pesticide residue analysis as well as its application in food analysis. The target compounds were analysed in solvent and in two representative food matrices such as cucumber (high water content) and egg (high fat content). MS data and intraday precision were similar in QqQ and IT, whereas interday precision was significantly worse in QqQ. Linearity (expressed as determination coefficient, R2) in the range 10–150 μg/l was adequate in both systems; however, better R2 values were obtained with the QqQ analyser in high and low concentration ranges (1–50 and 1–750 μg/l, respectively). The influence of the nature of the matrix on the analysis of low concentrations by each analyser was also evaluated. The QqQ and IT performance was similar in cucumber and solvent. However, QqQ provided better sensitivity in egg when in selected reaction monitoring (SRM) mode. Higher fragmentation was observed in the IT full scan spectra, and the precursor ions obtained from both systems were normally the same. Nevertheless, a number of exceptions, such as buprofezin, isocarbophos and isofenphos methyl, are illustrated in Fig. 2.7.

2.5 Validation of new analytical methods The development and the validation of analytical methods, including sample preparation and optimisation of the final instrumental determination, and implementation of quality assurance and quality control measures are, then, of the utmost importance to obtain reliable occurrence data on contaminants and decrease the uncertainty of the measurements. For a number of food contaminants and residues, European legislation establishes the maximum residue levels (MRLs or tolerances) permitted or minimum required performance limits (MRPLs) of the analytical method used to determine those banned in different food commodities, and also specifies the methods of sampling and analysis that should be used (e.g. for dioxins, dioxinlike PCBs and ethyl carbamate). For the latter, Commission Regulation No. 761/1999 prescribes GC-MS in single-ion-monitoring mode as the method of choice for the determination of ethyl carbamate in wines, and provides detailed information about the whole analytical procedure to be followed. For other compounds, rather than official or recommended methods, detailed performance criteria to be fulfilled by the methods of analysis used by the laboratories are specified (e.g. benzo[a]pyrene, pesticide residues). These performance criteria include recovery ranges, LODs, limits of quantification (LOQs) and precision

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Gas chromatography and mass spectroscopy techniques

39

Fig. 2.7 Full scan spectra of buprofezin, isocarbophos and isofenphos methyl obtained by GC-QqQ-MS/MS and GC-IT-MS/MS. (Reproduced from Garrido Frenich et al. 2008 with permission of Elsevier.)

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Chemical contaminants and residues in food

requirements. In this way, Commission Decision 2002/657/EC is probably the key document of legislation to be consulted by analytical laboratories in control of food safety (Anon 2002). This includes definitions and descriptions of how to assess trueness, recovery, repeatability and ruggedness, and detailed requirements for MS detection and identification of targeted substances. Although it lists performance criteria and other requirements for separation and detection techniques for both screening and confirmatory methods for analysis of food contaminants and residues in animal food products, this directive has been applied in many cases in which there are no well-established criteria. However, the current criteria established in official guidelines are not based on objective or empirical forms of measurement, but are based on arbitrary criteria using subjective assessments about the degree of selectivity provided by different MS techniques. The assessments are generally correct, but there are many exceptions, depending on the analyte–matrix pair, the concentration, the MS ions detected, the analytical technique and the importance of the results. The current rate of false negatives is thought to be too high because the identification criteria are too stringent. Furthermore, spurious errors are not typically addressed to reduce false positives, which are best addressed through confirmatory analysis. To illustrate this, there is a very interesting review by Lehotay et al. presenting some examples of real situations that have led the analyst either to make a misidentification or to take extra precautions in qualitative or quantitative MS analyses (Lehotay et al. 2008). The way to avoid these problems is to carry out interlaboratory studies. There are some interesting examples in the literature. An interlaboratory proficiency testing programme for melamine in milk was organised for field laboratories in Hong Kong, China, during the melamine crisis in late September 2008 (Ratel and Engel 2009). The performance of the participants was assessed by determining z-scores, calculated from the bias from the assigned reference values and Horwitz standard deviation. The median values of pooled data were found to be in good agreement with the reference values, and the majority of the participants demonstrated their capabilities in the quantitative measurement of melamine in milk samples. However, four participants gave false-positive results for the blank test sample, probably due to cross-contamination from other samples, and they were requested to investigate the actual causes. In summary, eight participants (or 62%) demonstrated their competence for all four test samples. This information gives a clear overview of the situation.

2.6 Applications and future trends The quality and safety of all types of food products is already a major issue around the world, and is becoming even more of an issue as populations grow and stretch already strained global food supplies even further. Such factors are driving the growth of analytical techniques, of which GC-MS is one of the more significant (Wright 2009). There are a large number of review papers dealing with the analysis

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Gas chromatography and mass spectroscopy techniques

41

of heat-induced contaminants (acrylamide, chloropropanols and furan) (Wenzl et al. 2007; Roberts et al. 2008; Tyan et al. 2009; Vranova and Ciesarova 2009; Keramat et al. 2011), bisphenol A (Ballesteros-Gomez et al. 2009), ethyl carbamates (Weber and Sharypov 2009), dioxins (De Pauw and Maghuin-Rogister 2006), mycotoxins (Santini et al. 2009; Koppen et al. 2010; Li et al. 2011b), melamine (Prieto et al. 2010), pesticides and their transformation products (Beyer and Biziuk 2008a; Gilbert-Lopez et al. 2009; Gonzalez-Rodriguez et al. 2009; Vidal et al. 2009; Barganska and Namiesnik 2010; Sharma et al. 2010; LeDoux 2011), PAHs (Plaza-Bolaños et al. 2010; Wretling et al. 2010), PBDEs (Vonderheide 2009), PCBs (Beyer and Biziuk 2008a; 2008b), polyfunctional amines and related compounds used as monomers and additives in food packaging materials (PaseiroCerrato et al. 2010), phthalate esters (Cao 2010) and veterinary drugs (Le Bizec et al. 2009; Parr et al. 2009; Baer et al. 2010) in different kinds of food. These reviews offer a global overview of the extraction methodologies, together with the separation and detection techniques, which are currently applied in the determination of each food contaminant or residue in food and beverages. The prominent role GC-MS plays within this field is unquestionably established. GC-MS meets the needs of target analyses well and largely provides the selectivity of measurement needed to assess compliance with food regulatory limits. However, to keep pace with the increased need for expanded analytical capability – faster throughput, more analytes per sample – chromatographic separation capability still needs to grow. In this respect, orthogonal separation techniques and multidimensional chromatography are key tools for the future (Gonzalez et al. 2007; Jackson 2009). Selected applications of the different GC-MS approaches since 2007 for determining food contaminants and residues are compiled in Table 2.3. Analysis of pesticide residues is by far the largest application area for GC-MS in food testing, but other potentially harmful contaminants, such as melamine, PCBs, dioxins, furan, acrylamine, PAHs and so on are adding to demand for such testing. From this application, it may be inferred that the analysis of food contaminants and residues by GC-MS is important for different fields of applications, highlighting quality control and safety in foods (Aiello et al. 2011). The high level of specificity and sensitivity of the GC-MS approach allows the characterisation of food components and contaminants present at ultra-trace levels, providing a distinctive and safe validation of the products. Within the applications of GC-MS, metabolomics has emerged as an important tool in many disciplines, such as human diseases and nutrition, drug discovery, plant physiology and others. In food science, metabolomics has recently become a tool for quality, processing and safety of raw materials and final products (Cevallos-Cevallos et al. 2009). GC-MS is a recognised tool in the field for profiling applications. The evaluation of dietary exposure (e.g. of secondary school students in Hong Kong to polybrominated diphenyl ethers from foods of animal origin (Chen et al. 2010)) is important for several reasons, such as determining temporal trends and assessing toxicity, bioaccessibility and uptake. Another interesting application area within food safety is how human exposure to such contaminants is assessed, and how contamination and exposure are combined with biological (toxicological) effects

© Woodhead Publishing Limited, 2012

Table 2.3 Analyte

Selected applications of GC-MS to food contaminants and residues according to the separation mode Matrix

Extraction

Injection

Separation

Detection

Characteristic

References

Splitless

HP5-MS

EI-qMS full scan

Positive identification for the first time of PBCDE

Hiebl et al. 2007

DB-5HT (15 m, 0.25 mm, 0.1 μm)

EI-HRMS (10 000 resolution and SIM mode)

Identification was confirmed by comparing the retention time, masses and ionabundance ratio of two exact m/z for each of the analytes

Chen et al. 2010

DB5MS (60 m, 0.25 mm, 0.25 μm)

EI-HRMS (10 000 resolution and SIM mode)

Uses a magnetic sector mass analyser

Menotta et al. 2010

DB5-ms (60 m, 0.25 mm, 0.25 μm)

EI-qMS (high resolution) in SIM (> 10 000 resolution)

–

Marti-Cid et al. 2008b

EI-QqQ-MS/ MS in SRM

Permitting both quantification Bolanos et al. 2007 and confirmation in a single injection with running time reduced by up to 17.70 min. LODs for pesticides were ≤2.25 μg/kg and LOQs ranged from 0.02 to 7.78 μg/kg. LODs for PCBs were ≤0.41 μg/kg and LOQ were ≤0.71 μg/kg

Conventional GC-MS

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HBCD

Eggs

Column extraction

PBCDE

Fish

n-hexane/acetone Clean up by GPC and fractionation in silica with hexane

PBDE

Food of animal origin

Dichloromethane– hexane and SPE through acid silica

PCDD/Fs and dioxinlike PCBs

Eggs

PLE with toluene and acid purification by SPE

HCB

Foodstuff widely consumed

Cold extraction with acetone–hexane and clean-up by GPC

PTV in splitless

57 OCPs, OPPs and PCBs

Eggs

MSPD using C18/ ethyl acetate (85:15, v/v) with a simultaneous clean-up with Florisil.

PTV in LVI VF-5ms (30 m, 0.25 mm, 0.25 μm)

(30 m, 0.25 mm, 0.25 μm)

Splitless

© Woodhead Publishing Limited, 2012

19 OCPs, OPPs pyrethroids

Eggs and vegetables

Vegetables: PTV with QuEChERS LVI (acetonitrile) Eggs: MSPD (C18 MgSO4) and simultaneous clean-up with Florisil

VF-5ms (30 m × 0.25 mm, 0.25 μm)

EI-QqQ-MS/ MS in SRM EI-IT-MS/MS in SMR

The MS data obtained by each Garrido Frenich et al. analyser were very similar 2008 within the group of studied compounds, although higher spectral information (complete product ion spectrum) was provided by the IT analyser GC-QqQ-MS/MS could be the most adequate option whenever the number of compounds is very high and fast analysis time is required. This analyser permits the application of easy sample pre-treatments and the reduction of the number of clean-up steps. Its lower robustness in comparison with the IT should be also taken into account

OPPs

Olive and advocado oil

APMAE and SPE (C18 and GCB) or low temperature fat precipitation

VF-5ms (30 m, 0.25 mm, 0.25 μm)

EI-QqQ-MS/ MS in SRM

The proposed method is simple Fuentes et al. 2009 and adequate to determine organophosphorus pesticides at sub-μg g−1 level in olive and avocado oil with a moderate consumption of solvent (25 ml per sample through the entire method) and good throughput

PTV

(Continued )

Table 2.3

Continued

© Woodhead Publishing Limited, 2012

Analyte

Matrix

Extraction

Injection

Separation

Detection

Characteristic

Pesticides

Medicinal herbs

MSPD with alumina and cyclohexane– Cl2CH2, on-line clean-up with C18

Splitless

DB-5MS(30 m, 0.25 mm, 0.25 μm)

EI-qMS in SIM A reported difficulty is that matrix components can cause variation in the detector response to pesticides. Consequently, the quantification of pesticide residues was carried out using matrix matched standards

de Carvalho et al. 2009

Pesticides

Sead weed

n-hexane/ethyl acetate (80:20) PLE with integrated clean-up (Florisil + GCB)

PTV-LVI

VF-5MS (30 m × 0.25 mm i.d., 0.25 μm)

EI-IT-MS/MS

GarciaRodriguez et al. 2010

The presence of pyrethroid and organophosphorus pesticides in some of the samples was evidenced. The optimum conditions of pressurised liquid extraction and LVI-GC-MS/ MS via PTV have been proven to be an efficient technology in the analysis of pesticides in seaweed at the parts per trillion level, improving the selectivity and sensitivity

References

© Woodhead Publishing Limited, 2012

Fungicides

Grapes

Ethyl acetate and PTV-split SPE (PSA and GCB) mode

SPB-5 (30 m × 0.25 mm, 0.25 μm)

EI-IT-MS

The addition of analyte Gonzalezprotectants (3-ethoxy-1,2Rodriguez propanediol, d-sorbitol and et al. 2009 l-gulonic acid γ-lactone) in the final extracts enabled the matrix-induced response enhancement effect on the quantitation process to be avoided, with absolute recoveries ca. 100

Fungicides

Grapes Ethyl acetate and during SPE vinification (Envi Carb-II/PSA)

PTV-split mode

SPB-5 (30 m × 0.25 mm, 0.25 μm)

EI-IT-MS

Application of the previous method

GonzalezRodriguez et al. 2011

Pesticides

QuEChERS Wheat grains, flour (acetonitrile) and bran

Electronic flow control (EFC)

VF-5 MS (30 m × 0.25 mm, 0.25 μm)

NCI-qMS in SIM

Operation parameters and evaluated performance characteristics of GC-MS with negative chemical ionisation for the analysis of multiple pesticides in wheat grains, white flour and bran were optimised

Kolberg et al. 2011c

Pesticides

Fruits and vegetables

Different QuEChERS methods

PTV

Restek Rtx 5-MS (20 m, 0.25 mm, 0.25 μm)

EI-high speed TOF-MS

The instrumental set-up was Lehotay capable of 2-dimensional GC, et al. 2010c but this feature was not used in this study

Pesticides

Grape

SiO2 hollow fibre

Splitless

AT.RPA-I (30 m × 0.32 mm, 0.33 μm)

EI-qMS in SIM Study devoted to the performance of the extraction procedures, not to GC determination

Li et al. 2011a

(Continued )

Table 2.3

Continued

Analyte

Matrix

Pesticides

Extraction

© Woodhead Publishing Limited, 2012

Injection

Separation

Detection

Characteristic

References

Drinking Cl2CH2 extraction. For cowpea and water, cowpea and maize: with PLE. maize grains

Splitless mode

HP-5MS (30 m, 0.25 mm i.d., 0.25 μm)

Mawussi EI-qMS in SIM Drinking water, maize and et al. 2009 cowpea grains contamination by various organochlorine pesticides (most of which are currently termed persistent organic pollutants) such as γ-HCH, DDTs, aldrin, dieldrin, endrin, heptachlor, heptachlor epoxide, and endosulfan were determined to estimate their human daily intake in cash crop (cocoa, coffee, cotton) cultivation areas in Togo

Pesticides

Peppers

QuEChERS (acetonitrile)

Splitless

HP-5MS (30 m × 0.25 mm, 0.25 μm)

Mezcua EI-qMS in SIM No significant differences in EI-IT-MS/MS performance between methods et al. 2009 were noticed in terms of in MRM sensitivity and limit of detection, although the unambiguous confirmation capabilities provided by MS/ MS cannot be achieved with a single quadrupole analyser

PAHs

Meat

n-hexane PLE and clean-up by GPC

PTV with SV in splitless

DB-17MS (60 m × 0.25 mm, 0.25 μm)

EI-qMS in SIM Compared with PTV injection in splitless mode, the PTV-SV injection method provided an enhancement of sensitivity for all target PAHs

Gomez-Ruiz et al. 2009

© Woodhead Publishing Limited, 2012

PAHs

Food-stuff widely consumed

Cold extraction with acetone–hexane and clean-up by GPC

PTV in splitless

DB5-ms (60 m, 0.25 mm, 0.25 μm)

EI-qMS (high resolution) in SIM (>10 000 resolution)

PAHs

Meat (heat treated and smoke curing)

Cyclohexane and N,Ndimethylformamide and clean-up silica column

Splitless

DB5-ms (60 m, 0.25 mm, 0.25 μm)

EI-qMS in SIM The results of GC-MS analysis Kuhn were in good agreement with et al. 2009 the effect-based bioassay

PAHs

Smoke meat and fish

Saponification (methanolic KOH) and extraction with cyclohexane

Splitless

DB-17 ms (30 m, 0.25 mm, 0.1 μm)

EI-qMS in SIM The method complies with the criteria for official control according to Commission Regulation (EC) No 333/2007

Bisphenol A and F

Tomato and HS-SPME using SWCNTs corn canned In situ derivatisation

Thermal HP5-capillary column EI-qMS in SIM desorption– (30 m, 0.25 mm i.d., PTV 0.25 μm film thickness) injector

Furan

Jarred baby HS food

Split (ratio 1:10)

Furan

Baby food

Thermal HP-INNOWAX (60 m, EI-qMS in SIM Validation was carried out according to the criteria desorption- 0.25 mm, 0.5 μm) stipulated in Decision PTV 2002/657

SPME 75 μm carboxen– PDMS

HP-PLOT Q (15 m, 0.32 mm, 20 μm)

Marti-Cid et al. 2008a

A comparative study between SWCNT and a commercial PDMS fibre. SWCNT fibre showed higher extraction capacity, better thermal stability (over 350 °C) and longer lifespan (over 150 times) than the commercial PDMS fibre

EI-qMS in SIM Validation was performed according to ISO 17025 and EFSA requirements

Wretling et al. 2010

Goicoechea et al. 2008

Ruiz et al. 2010 Arisseto et al. 2010

(Continued )

Table 2.3

Continued

© Woodhead Publishing Limited, 2012

Analyte

Matrix

Extraction

Injection

Separation

Detection

Characteristic

References

3-MCPD and its fatty acid esters

Infant and baby food

Solvent extraction hexane–diethyl ether

Pulsed splitless

Equity 1 (30 m, 0.25 mm, 1 μm) DB-1HT (15 m, 0.25 mm, 0.1 μm) HP-Innowax (30 m, 0.25 mm, 0.5 μm)

EI-qMS in SIM While none of the products Zelinkova contained free chloropropanols et al. 2008 at levels exceeding the method LODs, all of them contain relatively high amounts of 3-MCPD esters

Phthalate esters

Wine

SPE C18 and Cl2CH2

Splitless

Rtx-5ms (30 m, 0.25 mm, 0.25 μm)

EI-qMS in SIM GC-MS is used for the Del Carlo identification (full scan mode) et al. 2008 and quantification (SIM mode)

Pesticides

Advocado, olive oil

Acetonitrile APMAE Split/ and SPE or low splitless temperature fat PTV precipitation

5% phenyl–95% dimethylpolysiloxane (30 m × 0.25 mm i.d., 0.25 μm)

EI-QqQ-MS/ MS

The proposed method is simple Fuentes et al. 2009 and adequate to determine organophosphorus pesticides at sub-μg g−1 level in olive and avocado oil

Baby food

QuEChERS (acetonitrile buffered) Ethyl acetate and GPC

Rtx-5 Sil MS (10 m × 0.53 mm i.d., 0.5 μm)

EI-HRTOF-MS

LP chromatography: Cajka high temperature and et al. 2008 vacuum conditions in a megabore column Comparison with conventional GC and GC×GC

Fast GC-MS Pesticides

PTV in SV mode

Cunha et al. LP chromatography: high 2009 temperature and vacuum conditions in a megabore column After optimization, all 27 pesticides were extracted, chromatographically separated and detected in less than 20 min

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Pesticides

Grape, must and wines

QuEChERS (acetonitrile)

Split/ splitless

Supelco SPB-5 (15 m × EI-MS in SIM 0.32 mm I.D., 1.0 μm) connected to a 3 m × 0.25 mm I.D. non-coated restriction column (Supelco) at the inlet end

Pesticides

Fruits and vegetables

QuEChERS (acetonitrile)

PTV/LVI

Rti-5ms (10 m × 0.53 mm × 1 μm) coupled to a 3 m × 0.15 mm i.d. non-coated restriction capillary at the inlet

Animal derived products

HS-SPME 75 μm carboxen– PDMS

Thermal desorption

EI-high Sevenfold increase in the GC×GC speed-TOF-MS contaminants detected DB-5 compared with GC-qMS (30 m, 0.25 mm, 0.25 μ) DB-17 (2 m, 0.1 mm, 0.1 μm)

EI-high The results indicate that speed-TOF-MS LP-GC/TOF-MS for GC-amenable analytes matches UHPLC-MS/MS in terms of sample throughput and turnaround time for their routine, concurrent use in the analysis of a wide range of analytes in QuEChERS extracts to achieve reliable quantification and identification of pesticide residues in foods

Koesukwiwat et al. 2010b

GC×GC Benzenic and halogenated VOCs

Ratel et al. 2009

(Continued )

Table 2.3

Continued

© Woodhead Publishing Limited, 2012

Analyte

Matrix

Extraction

Injection

Separation

Detection

Characteristic

References

17 PCDD/Fs 4 non-ortho PCBs

Fish oil

Ethyl acetate extraction, clean-up by GPC and SPE with PSA or by GPC and SPE on GBC

PTV

GC×GC RTX-CL (30 m, 0.25 mm, 0.25 μm) BPX-50 (2 m, 0.1 mm, 0.1 μm)

EI-high speed TOF-MS

A method based on GC×GCTOF-MS is suitable for both qualitative screening and quantitative determination of a wide range of pesticides and contaminants in complex feed samples at μg/kg levels

van der Lee et al. 2008

17 PCDD/Fs 4 non-ortho PCBs

Fish oil

GPC and SPE on GCB

DSI

GC×GC

EI-high speed TOF-MS

Interesting capabilities of identification

Hoh et al. 2008b

POPs

Fish oil

GPC and SPE on GCB

DSI

GC×GC

EI-high speed TOF-MS

Seven DMBP congeners are reported for the first time

Hoh et al. 2009a

PCBs, PCDD/ Fish oil Fs, PBDE and HNPs

GPC and SPE on GCB

DSI

GC×GC Restek Rtx-5Sil-MS (15 m, 0.25 mm, 0.25 μm) DB-17MS (2 m, 0.18 mm, 0.18 μm)

EI-high speed TOF-MS

To simplify the analysis without affecting overall PCB quantitation, 15 PCB congeners were used Some PBDEs, oxybenzone and a dibromoindole were also detected in the ‘blank’ samples

Hoh et al. 2009b

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PCBs, PCDD/ Fish oil Fs,

GPC and SPE on GBC

DSI

EI-high speed GC×GC TOF-MS Restek Siltek deactivated column (4 m, 0.25 mm i.d.) as a guard column Restek Rtx-Dioxin 2 (60 m, 0.25 mm i.d., 0.25 μm) (1D) Rtx-PCB (3 m, 0.18 mm, 0.18 μm) (2D)

Hoh et al. Comparison with traditional 2008a gas chromatography – high resolution mass spectrometry (GC-HRMS) Good agreement of results for standard solutions analysed in blind fashion Relatively high tolerance of the DSI technique for lipids in the final extracts enabled a streamlined sample preparation procedure

PCDDs/Fs

Standard solutions

——

DSI

EI-high speed GC×GC TOF-MS Rtx-Dioxin 2 (60 m, 0.25 mm I.D., 0.25 μm) Rtx-PCB (2 m, 0.18 mm, 0.18 μm)

The operating parameters of GC×GC-TOF-MS were evaluated and optimised for the analysis

Pesticides

Flaxseeds, Modified QuEChERS, which Peanuts, and Doughs was previously optimised for cereal grain.

Splitless

GC×GC Rtx-5MS (20 m × 0.25 mm i.d. × 0.25 μm) Rtx-CPL Pesticides II (1.5 m × 0.10 mm × 0.10 μm)

EI-high Good separation, linearity and speed-TOF-MS reproducibility of most target pesticides were achieved by this method

Hoh et al. 2007

Koesukwiwat et al. 2010a

Notes: 3-MCPD, 3-chloropropane-1,2-diol; APMAE, atmospheric pressure microwave-assisted liquid-liquid extraction; DMBP, 1,1ʹ-dimethyl-2,2ʹ-bipyrroles; DSI, direct sample introduction; EI, electron impact; GCB, grafitized carbon black; GPC, gel permeation chromatography; HBCD, hexabromocyclododecane; HCB, hexachlorobenzene; HCH, hexachlorocyclohexane; HNP, halogenated natural products; HR, high resolution; HS, headspace; LOD, limit of detection; LOQ, limit of quantification; LP, low pressure; LVI, large volume injection; MRM, multiple reaction monitoring; MSPD, matrix solid-phase dispersion; m/z, mass-to-charge ratio; NCI, negative chemical ionization; OCP, organochlorine pesticide; OPP, organophosphorus pesticide; PAH, polycyclic aromatic hydrocarbons; PBCDE, pentabromocyclododecene; PBDE, polybrominated diphenyl ether; PCB, polychlorinated biphenyls; PCDD/F, polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran; PDMS, polydimethylsiloxane; PLE, pressurized liquid extraction; PSA, primary secondary amine; PTV, programmed-temperature injection; qMS, quadrupole mass spectrometer; SPE, solid phase extraction; SV, solvent venting mode.

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Chemical contaminants and residues in food

for risk assessment is one of the key points on the implementation of the information that can be obtained by GC (Dorne et al. 2009). The huge number of publications and the wide range of application areas already indicate that GC-MS is a powerful analytical tool. The application of more selective mass spectrometers (TOF, QqQ and IT) results in a significant expansion of the application area of GC within the field of food contaminants and residue analysis. GC-MS has great potential. In particular, the hyphenation of liquid-phase or solid-phase separation methods and GC-MS has improved the sensitivity of the determination. The systems developed for automated on-line desorption by SPME, SBSE and LPME allowed better sensitivity to be obtained. Other liquidphase separation methods, such as gradient RPLC, have also been hyphenated to GC using similar principles (Cortes et al. 2009). An improved level of detail can also be obtained through the use of comprehensive two-dimensional GC (GC×GC) instead of the commonly used 1D-GC, achieving the separation of complex mixtures (e.g. PCBs, dioxins or OCPs), which is especially relevant for the characterisation of food samples in which a large number of different contaminants and food components can be expected. The huge peak capacity of this technique has allowed the use of entirely new strategies for extracting information from samples: profiling instead of target compounds analysis. GC×GC will improve the identification and quantification of the analytes of interest and will also enable group-type identification/classification and quantification. Finally, chemometric methods can greatly improve our ways of extracting information from complex chromatograms. Advanced chemometrics can aid in the interpretation of complex fingerprints as well as in detecting small differences or similarities in chromatograms. With the proper chemometric tools it will be easier to convert detailed datasets obtained for complex samples into useful information. GC and GC×GC here provide the highest resolution and excellent sensitivity.

2.7 Acknowledgements This work has been supported by the Spanish Ministry of Science and Innovation through the projects Consolider-Ingenio 2010 CSD2009-00065 and CGL201129703-C02-02.

2.8

Sources of further information

Allielo et al. (2011) review the application of multistage mass spectrometry in quality, safety and origin of foods, including the hyphenation between GC and MS. Applications in proteomics, allergonomics, glycomics, metabolomics, lipidomics, food safety and traceability are also surveyed.

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Alder et al. (2006) evaluate the capabilities of MS in combination with GC and LC for the determination of a multitude of pesticides. Bartle and Myers (2002) describe the major milestones in the development of GC, especially in column technology, detection and sample introduction in a historical review. Cajka and Hajslova (2007) show how GC-TOF-MS offers unique solutions for various analytical applications including the analysis of food quality, authenticity and safety markers. This article provides a general overview of TOF-MS basic features, highlighting its advantages and limitations compared with GC using conventional mass analysers. Examples of recent results obtained for selected food contaminants and flavour components are described to illustrate the potential of this recently introduced technique. Domotorova and Matisova (2008) provide an overview of fast GC methods for analysis of pesticide residues in a variety of matrices at ultra-trace concentration levels. Donato et al. (2007) describe the high-speed injection systems, electronic gas pressure control, rapid oven heating/cooling and fast detection that are currently available in a variety of commercial gas chromatographs. Hajslova and Cajka (2007) present the optimisation of operations involved in the final phase of food toxicant analysis by GC-MS: (i) introduction of sample extract onto the GC column, (ii) separation of its components on an analytical column and (iii) detection of target analytes by the most commonly used mass spectrometry detectors. Hernandez et al. (2011) discuss in detail the characteristics and the potential of GC-HR-TOF-MS and describe different analytical strategies from wide-scope target screening to investigation of unknowns in biology, the environment and food safety. Herrero et al. (2009) review the main developments and applications of multidimensional chromatographic techniques in food analysis. Different aspects related to the existing couplings involving chromatographic techniques are examined. These couplings include multidimensional GC, multidimensional LC and multidimensional SFC as well as all their possible combinations. Hoh and Mastovska (2008) assess the currently available LVI techniques, including basic approaches to their optimisation and important real-world applications. The most common LVI methods are on-column and programmed temperature vaporisation (PTV) in solvent rent mode. Newer techniques discussed in this article include direct sample introduction (DSI), splitless overflow, at-column, and ‘through oven transfer adsorption desorption’ (TOTAD). Hyötyläinen et al. (2008) critically overview the principles and benefits of extraction coupled on-line with GC. Techniques suitable for the extraction and analysis of various types of compounds in both solid and liquid samples are presented too. Lehotay and Hajslova (2002) give a general idea of the many uses of GC in food analysis in comparison to high-performance liquid chromatography (HPLC) and mention state-of-the-art GC techniques used in the major applications. Past

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and current trends are assessed, and anticipated future trends in GC for food applications are predicted. Ravindra et al. (2008) describe the concept of LP-GC and explore its recent developments and applications with a focus on the use of various column systems and analysers.

2.9

References

ADENUGBA, A. A., HEADLEY, J., MCMARTIN, D.

and BECK, A. J. (2008), ‘Comparison of levels of polychlorinated biphenyls in edible oils and oil-based products – possible link to environmental factors’, J. Environ. Sci. Health B, 43, 422–428. AHIRE, K. C., ARORA, M. S. and MUKHERJEE, S. N. (2008), ‘Development and application of a method for analysis of lufenuron in wheat flour by gas chromatography-mass spectrometry and confirmation of bio-efficacy against Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)’, J. Chromatogr. B, 861, 16–21. AIELLO, D., DE LUCA, D., GIONFRIDDO, E., NACCARATO, A., NAPOLI, A. et al. (2011), ‘Multistage mass spectrometry in quality, safety and origin of foods’, Eur. J. Mass Spectrom., 17, 1–31. ALDER, L., GREULICH, K., KEMPE, G. and VIETH, B. (2006), ‘Residue analysis of 500 high priority pesticides: Better by GC-MS or LC-MS/MS?’, Mass Spectrom. Rev., 25, 838–865. ALTAKI, M. S., SANTOS, F. J. and GALCERAN, M. T. (2009), ‘Automated headspace solid-phase microextraction versus headspace for the analysis of furan in foods by gas chromatography-mass spectrometry’, Talanta, 78, 1315–1320. ARISSETO, A., VICENTE, E. and TOLEDO, M. C. D. (2010), ‘Determination of furan levels in commercial samples of baby food from Brazil and preliminary risk assessment’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 27, 1051–1059. AYSAL, P., AMBRUS, A., LEHOTAY, S. J. and CANNAVAN, A. (2007), ‘Validation of an efficient method for the determination of pesticide residues in fruits and vegetables using ethyl acetate for extraction’, J. Environ. Sci. Health B, 42, 481–490. BAER, I., DE LA CALLE, B. and TAYLOR, P. (2010), ‘3-MCPD in food other than soy sauce or hydrolysed vegetable protein (HVP)’, Anal. Bioanal. Chem., 396, 443–456. BALLESTEROS-GOMEZ, A., RUBIO, S. and PEREZ-BENDITO, D. (2009), ‘Analytical methods for the determination of bisphenol A in food’, J. Chromatog. A, 1216, 449–469. BARGANSKA, Z. and NAMIESNIK, J. (2010), ‘Pesticide analysis of bee and bee product samples’, Crit. Rev. Anal. Chem., 40, 159–171. BARRIADA-PEREIRA, M., SERODIO, P., GONZALEZ-CASTRO, M. J. and NOGUEIRA, J. M. F. (2010), ‘Determination of organochlorine pesticides in vegetable matrices by stir bar sorptive extraction with liquid desorption and large volume injection-gas chromatography-mass spectrometry towards compliance with European Union directives’, J. Chromatogr. A, 1217, 119–126. BARTLE, K.D., MYERS, P. (2002), History of gas chromatography. TrAC, Trends Anal. Chem. 21: 547–557. BEYER, A. and BIZIUK, M. (2008a), ‘Methods for determining pesticides and polychlorinated biphenyls in food samples – problems and challenges’, Crit. Rev. Food Sci. Nutr., 48, 888–904. BEYER, A. and BIZIUK, M. (2008b), ‘Applications of sample preparation techniques in the analysis of pesticides and PCBs in food’, Food Chemistry, 108, 669–680. BLANES, M. A., SERRANO, R. and LOPEZ, F. J. (2009), ‘Seasonal trends and tissue distribution of organochlorine pollutants in wild and farmed gilthead sea bream (Sparus aurata) from

© Woodhead Publishing Limited, 2012

Gas chromatography and mass spectroscopy techniques

55

the Western Mediterranean sea and their relationship with environmental and biological factors’, Arch. Environ. Contam. Toxicol., 57, 133–144. BOLANOS, P. P., FRENICH, A. G. and VIDAL, J. L. M. (2007), ‘Application of gas chromatographytriple quadrupole mass spectrometry in the quantification-confirmation of pesticides and polychlorinated biphenyls in eggs at trace levels’, J. Chromatogr. A, 1167, 9–17. CAJKA, T. and HAJSLOVA, J. (2007), ‘Gas chromatography-time-of-flight mass spectrometry in food analysis’, LC GC Europe, 20, 25–26, 28–31. CAJKA, T., HAJSLOVA, J., LACINA, O., MASTOVSKA, K. and LEHOTAY, S. J. (2008), ‘Rapid analysis of multiple pesticide residues in fruit-based baby food using programmed temperature vaporiser injection-low-pressure gas chromatography-high-resolution timeof-flight mass spectrometry’, J. Chromatogr. A, 1186, 281–294. CALIGIANI, A., PALLA, G., BONZANINI, F., BIANCHI, A. and BRUNI, R. (2011), ‘A validated GC-MS method for the detection of tropane alkaloids in buckwheat (Fagopyron esculentum L.) fruits, flours and commercial foods’, Food Chemistry, 127, 204–209. CANTERINO, M., MAROTTA, R., TEMUSSI, F. and ZARRELLI, A. (2008), ‘Photochemical behaviour of musk tibetene – a chemical and kinetic investigation’, Environ. Sci. Pollut. Res., 15, 182–187. CAO, X. L. (2010), ‘Phthalate esters in foods: Sources, occurrence, and analytical methods’, Comp. Rev. Food Sci. Food Safety, 9, 21–43. CEVALLOS-CEVALLOS, J. M., REYES-DE-CORCUERA, J. I., ETXEBERRIA, E., DANYLUK, M. D. and RODRICK, G. E. (2009), ‘Metabolomic analysis in food science: a review’, Trends Food Sci. Technol., 20, 557–566. CHEN, M. Y. Y., TANG, A. S. P., HO, Y. Y. and XIAO, Y. (2010), ‘Dietary exposure of secondary school students in Hong Kong to polybrominated diphenyl ethers from foods of animal origin’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 27, 521–529. COELHO, E., PERESTRELO, R., NENG, N. R., CGMARA, J. S., COIMBRA, M. A., NOGUEIRA, J. M. F. and ROCHA, S. M. (2008), ‘Optimisation of stir bar sorptive extraction and liquid desorption combined with large volume injection-gas chromatography-quadrupole mass spectrometry for the determination of volatile compounds in wines’, Anal. Chim. Acta, 624, 79–89. CORTES, J. M., VAZQUEZ, A., SANTA-MARIA, G., BLANCH, G. P. and VILLÉN, J. (2009), ‘Pesticide residue analysis by RPLC-GC in lycopene and other carotenoids obtained from tomatoes by supercritical fluid extraction’, Food Chemistry, 113, 280–284. CREWS, C. (2010), ‘The determination of N-nitrosamines in food’, Qual. Assur. Saf. Crop., 2, 2–12. CUNHA, S. C., FERNANDES, J. O., ALVES, A. and OLIVEIRA, M. B. P. P. (2009), ‘Fast low-pressure gas chromatography-mass spectrometry method for the determination of multiple pesticides in grapes, musts and wines’, J. Chromatogr. A, 1216, 119–126. CUS, F., CESNIK, H. B., BOLTA, S. V. and GREGORCIC, A. (2010), ‘Pesticide residues in grapes and during vinification process’, Food Control, 21, 1512–1518. DAVIES, I. W. (2000), ‘Gas chromatography: Sampling systems’, in Ian, D. W., ed., Encyclopedia of Separation Science, Academic Press, Oxford, pp. 550–558. DE CARVALHO, P. H. V., PRATA, V. D., ALVES, P. B. and NAVICKIENE, S. (2009), ‘Determination of six pesticides in the medicinal herb Cordia salicifolia by matrix solid-phase dispersion and gas chromatography/mass spectrometry’, J. AOAC Int., 92, 1184–1189. DE JAGER, L. S., PERFETTI, G. A. and DIACHENKO, G. W. (2008), ‘Analysis of tetramethylene disulfotetramine in foods using solid-phase microextraction-gas chromatography-mass spectrometry’, J. Chromatogr. A, 1192, 36–40. DE PAUW, E. and MAGHUIN-ROGISTER, G. (2006), ‘Residues and contaminants in food: 25 years of progress in their analysis. IV. Dioxins and other contaminants. Methods based on mass spectrometry’, Ann. Med. Vet., 150, 163–166. DEL CARLO, M., PEPE, A., SACCHETTI, G., COMPAGNONE, D., MASTROCOLA, D. and CICHELLI, A. (2008), ‘Determination of phthalate esters in wine using solid-phase extraction and gas chromatography-mass spectrometry’, Food Chemistry, 111, 771–777.

© Woodhead Publishing Limited, 2012

56

Chemical contaminants and residues in food

DOMOTOROVA, M. and MATISOVA, E. (2008), ‘Fast gas chromatography for pesticide residues

analysis’, J. Chromatogr. A, 1207, 1–16. DONATO, P., TRANCHIDA, P. Q., DUGO, P., DUGO, G.

and MONDELLO, L. (2007), ‘Rapid analysis of food products by means of high speed gas chromatography’, J. Sep. Sci., 30, 508–526. DORNE, J. L. C. M., BORDAJANDI, L. R., AMZAL, B., FERRARI, P. and VERGER, P. (2009), ‘Combining analytical techniques, exposure assessment and biological effects for risk assessment of chemicals in food’, TrAC, Trends Anal. Chem., 28, 695–707. EUROPEAN COMMISSION (2002), ‘Commission Decision of 12 August 2002 implementing Council Directive 96/23/EC concerning the performance of analytical methods and the interpretation of results’, Official Journal of the European Communities, L221, 8–36. Brussels, European Communities. FIALKOV, A. B., STEINER, U., LEHOTAY, S. J. and AMIRAV, A. (2007), ‘Sensitivity and noise in GC-MS: achieving low limits of detection for difficult analytes’, Int. J. Mass Spectrom., 260, 31–48. FUENTES, E., BAEZ, M. E. and DIAZ, J. (2009), ‘Microwave-assisted extraction at atmospheric pressure coupled to different clean-up methods for the determination of organophosphorus pesticides in olive and avocado oil’, J. Chromatogr. A, 1216, 8859–8866. FUSSELL, R. J., CHAN, D. and SHARMAN, M. (2010), ‘An assessment of atmospheric-pressure solids-analysis probes for the detection of chemicals in food’, TrAC Trends Anal. Chem., 29, 1326–1335. GARCIA-RODRIGUEZ, D., CARRO-DIAZ, A. M., LORENZO-FERREIRA, R. A. and CELA-TORRIJOS, R. (2010), ‘Determination of pesticides in seaweeds by pressurized liquid extraction and programmed temperature vaporization-based large volume injection-gas chromatography-tandem mass spectrometry’, J. Chromatogr. A, 1217, 2940–2949. GARRIDO FRENICH, A., PLAZA-BOLAÑOS, P. and VIDAL, J. L. M. (2008), ‘Comparison of tandemin-space and tandem-in-time mass spectrometry in gas chromatography determination of pesticides: Application to simple and complex food samples’, J. Chromatogr. A, 1203, 229–238. GARTNER, S., BALSKI, M., KOCH, M. and NEHLS, I. (2009), ‘Analysis and migration of phthalates in infant food packed in recycled paperboard’, J. Agric. Food Chem., 57, 10675–10681. GILBERT-LOPEZ, B., GARCIA-REYES, J. F. and MOLINA-DIAZ, A. (2009), ‘Sample treatment and determination of pesticide residues in fatty vegetable matrices: A review’, Talanta, 79, 109–128. GOICOECHEA, E., VAN TWILLERT, K., DUITS, M., BRANDON, E. D. F. A., KOOTSTRA, P. R., et al. (2008), ‘Use of an in vitro digestion model to study the bioaccessibility of 4-hydroxy-2nonenal and related aldehydes present in oxidized oils rich in omega-6 acyl groups’, J. Agric. Food Chem., 56, 8475–8483. GOMEZ-RUIZ, J. A., CORDEIRO, F., LOPEZ, P. and WENZL, T. (2009), ‘Optimisation and validation of programmed temperature vaporization (PTV) injection in solvent vent mode for the analysis of the 15 + 1 EU-priority PAHs by GC-MS’, Talanta, 80, 643–650. GONZALEZ, R. R., MORENO, J. L. F., BOLANOS, P. P., FRENICH, A. G. and VIDAL, J. L. M. (2007), ‘Using mass spectrometry as a tool for testing for toxic substances in foods: toward food safety’, Rev. Esp. Salud Publica, 81, 461–474. GONZALEZ-RODRIGUEZ, R. M., CANCHO-GRANDE, B., SIMAL-GANDARA, J. (2009), Multiresidue determination of 11 new fungicides in grapes and wines by liquid-liquid extraction/ clean-up and programmable temperature vaporization injection with analyte protectants/ gas chromatography/ion trap mass spectrometry, Journal of Chromatography A, 1216, 6033–6042. GONZALEZ-RODRIGUEZ, R. M., CANCHO-GRANDE, B. and SIMAL-GANDARA, J. (2011), ‘Decay of fungicide residues during vinification of white grapes harvested after the application of some new active substances against downy mildew’, Food Chemistry, 125, 549–560. GUENTHER, H., HOENICKE, K., BIESTERVELD, S., GERHARD-RIEBEN, E. and LANTZ, I. (2010), ‘Furan in coffee: pilot studies on formation during roasting and losses during production

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Gas chromatography and mass spectroscopy techniques

57

steps and consumer handling’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 27, 283–290. HAJSLOVA, J. and CAJKA, T. (2007), ‘Gas chromatography-mass spectrometry (GC-MS)’, in Yolanda, P. (ed.), Food Toxicants Analysis, Elsevier, Amsterdam, pp. 419–473. HAKKARAINEN, M. (2008), ‘Solid phase microextraction for analysis of polymer degradation products and additives’. In: Chromatography for sustainable polymeric materials, Albertsson, A.C. and Hakkarainen, M. (eds) vol. 211, Serie Advances in Polymer Science, Springer Verlag, Berlin, pp. 23–50. HERNANDEZ, F., PORTOLES, T., PITARCH, E. and LOPEZ, F. J. (2007), ‘Target and nontarget screening of organic micropollutants in water by solid-phase microextraction combined with gas chromatography/high-resolution time-of-flight mass spectrometry’, Anal. Chem., 79, 9494–9504. HERNANDEZ, F., PORTOLES, T., PITARCH, E. and LOPEZ, F. J. (2011), ‘Gas chromatography coupled to high-resolution time-of-flight mass spectrometry to analyze trace-level organic compounds in the environment, food safety and toxicology’, TrAC Trends Anal. Chem., 30, 388–400. HERRERO, M., IBAN ˜ EZ, E., CIFUENTES, A. and BERNAL, J. (2009), ‘Multidimensional chromatography in food analysis’, Journal of Chromatography A, 1216, 7110–7129. HIEBL, J. and VETTER, W. (2007), ‘Detection of hexabromocyclododecane and its metabolite pentabromocyclododecene in chicken egg and fish from the official food control’, J. Agric. Food Chem., 55, 3319–3324. HOH, E. and MASTOVSKA, K. (2008), ‘Large volume injection techniques in capillary gas chromatography’, J. Chromatogr. A, 1186, 2–15. HOH, E., MASTOVSKA, K. and LEHOTAY, S. J. (2007), ‘Optimization of separation and detection conditions for comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans’, J. Chromatogr. A, 1145, 210–221. HOH, E., LEHOTAY, S. J., MASTOVSKA, K. and HUWE, J. K. (2008), ‘Evaluation of automated direct sample introduction with comprehensive two-dimensional gas chromatography/ time-of-flight mass spectrometry for the screening analysis of dioxins in fish oil’, J. Chromatogr. A, 1201, 69–77. HOH, E., LEHOTAY, S. J., MASTOVSKA, K., NGO, H. L., VETTER, W. et al. (2009a), ‘Capabilities of direct sample introduction-comprehensive two-dimensional gas chromatographytime-of-flight mass spectrometry to analyze organic chemicals of interest in fish oils’, Environ. Sci. Technol., 43, 3240–3247. HOH, E., LEHOTAY, S. J., PANGALLO, K. C., MASTOVSKA, K., NGO, H. L. et al. (2009b), ‘Simultaneous quantitation of multiple classes of organohalogen compounds in fish oils with direct sample introduction comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry’, J. Agric. Food Chem., 57, 2653–2660. HYÖTYLÄINEN, T. (2008), ‘On-line coupling of extraction with gas chromatography’, J. Chromatogr. A, 1186, 39–50. JACKSON, L. S. (2009), ‘Chemical food safety issues in the United States: past, present, and future’, J. Agric. Food Chem., 57, 8161–8170. KERAMAT, J., LEBAIL, A., PROST, C. and SOLTANIZADEH, N. (2011), ‘Acrylamide in foods: chemistry and analysis. A review’, Food Bioprocess Tech., 4, 340–363. KIM, T. K., KIM, S. and LEE, K. G. (2010), ‘Analysis of furan in heat-processed foods consumed in Korea using solid phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS)’, Food Chemistry, 123, 1328–1333. KLIMANKOVA, E., RIDDELLOVA, K., HAJSLOVA, J., POUSTKA, J., KOLAROVA, J. and KOCOUREK, V. (2008), ‘Development of an SPME-GC-MS/MS procedure for the monitoring of 2-phenoxyethanol in anaesthetised fish’, Talanta, 75, 1082–1088. KMELLAR, B., ABRANKO, L., FODOR, P. and LEHOTAY, S. J. (2010), ‘Routine approach to qualitatively screening 300 pesticides and quantification of those frequently detected in fruit and vegetables using liquid chromatography tandem mass spectrometry (LC-MS/

© Woodhead Publishing Limited, 2012

58

Chemical contaminants and residues in food

MS)’, Food Addit. Contam. Part A-Chemistry Analysis Control Exposure & Risk Assessment, 27, 1415–1430. KOESUKWIWAT, U., LEHOTAY, S. J., MASTOVSKA, K., DORWEILER, K. J. and LEEPIPATPIBOON, N. (2010a), ‘Extension of the QuEChERS method for pesticide residues in cereals to flaxseeds, peanuts, and doughs’, J. Agric. Food Chem., 58, 5950–5958. KOESUKWIWAT, U., LEHOTAY, S. J., MIAO, S. and LEEPIPATPIBOON, N. (2010b), ‘High throughput analysis of 150 pesticides in fruits and vegetables using QuEChERS and low-pressure gas chromatography-time-of-flight mass spectrometry’, J. Chromatogr. A, 1217, 6692–6703. KOLBERG, D. I., PRESTES, O. D., ADAIME, M. B. and ZANELLA, R. (2011), ‘Development of a fast multiresidue method for the determination of pesticides in dry samples (wheat grains, flour and bran) using QuEChERS based method and GC-MS’, Food Chemistry, 125, 1436–1442. KOPPEN, R., KOCH, M., SIEGEL, D., MERKEL, S., MAUL, R. and NEHLS, I. (2010), ‘Determination of mycotoxins in foods: current state of analytical methods and limitations’, Appl. Microbiol. Biotechnol., 86, 1595–1612. KUHN, K., NOWAK, B., BEHNKE, A., SEIDEL, A. and LAMPEN, A. (2009), ‘Effect-based and chemical analysis of polycyclic aromatic hydrocarbons in smoked meat: a practical food-monitoring approach’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 26, 1104–1112. LAMBROPOULOU, D. A., KONSTANTINOU, I. K. and ALBANIS, T. A. (2007), ‘Recent developments in headspace microextraction techniques for the analysis of environmental contaminants in different matrices’, J. Chromatogr. A, 1152, 70–96. LANCAS, F. M., QUEIROZ, M. E. C., GROSSI, P. and OLIVARES, I. R. B. (2009), ‘Recent developments and applications of stir bar sorptive extraction’, J. Sep. Sci., 32, 813–824. LE BIZEC, B., PINEL, G. and ANTIGNAC, J. P. (2009), ‘Options for veterinary drug analysis using mass spectrometry’, J. Chromatogr. A, 1216, 8016–8034. LEDOUX, M. (2011), ‘Analytical methods applied to the determination of pesticide residues in foods of animal origin. A review of the past two decades’, J. Chromatogr. A, 1218, 1021–1036. LEHOTAY, S. J. and HAJSLOVA, J. (2002), ‘Application of gas chromatography in food analysis’, TrAC Trends Anal. Chem., 21, 686–697. LEHOTAY, S. J., MASTOVSKA, K., AMIRAV, A., FIALKOV, A. B., MARTOS, P. A. et al. (2008), ‘Identification and confirmation of chemical residues in food by chromatography-mass spectrometry and other techniques’, TrAC Trends Anal. Chem., 27, 1070–1090. LEHOTAY, S. J., ANASTASSIADES, M. and MAJORS, R. E. (2010a), ‘QuEChERS, a sample preparation technique that is “catching on”: an up-to-date interview with the inventors’, LC GC North America, 28, 504–516. LEHOTAY, S. J., ANASTASSIADES, M. and MAJORS, R. E. (2010b), ‘The QuEChERS revolution’, LC GC Europe, 23, 418–425. LEHOTAY, S. J., SON, K. A., KWON, H., KOESUKWIWAT, U., FU, W. S. et al. (2010c), ‘Comparison of QuEChERS sample preparation methods for the analysis of pesticide residues in fruits and vegetables’, J. Chromatogr. A, 1217, 2548–2560. LEÓN, N., YUSÀ, V., PARDO, O. and PASTOR, A. (2008), ‘Determination of 3-MCPD by GC-MS/ MS with PTV-LV injector used for a survey of Spanish foodstuffs’, Talanta, 75, 824–831. LI, J., ZHANG, H. F. and SHI, Y. P. (2011a), ‘Monitoring multi-class pesticide residues in fresh grape by hollow fibre sorptive extraction combined with gas chromatography-mass spectrometry’, Food Chemistry, 127, 784–790. LI, Y. S., WANG, Z. H., BEIER, R. C., SHEN, J. Z., DE SMET, D. et al. (2011b), ‘T-2 toxin, a trichothecene mycotoxin: review of toxicity, metabolism, and analytical methods’, J. Agric. Food Chem., 59, 3441–3453. MALIK, A. K., BLASCO, C. and PICO, Y. (2010), ‘Liquid chromatography-mass spectrometry in food safety’, J. Chromatogr. A, 1217, 4018–4040. MARTI-CID, R., LLOBET, J. M., CASTELL, V. and DOMINGO, J. L. (2008a), ‘Evolution of the dietary exposure to polycyclic aromatic hydrocarbons in Catalonia, Spain’, Food Chem. Toxicol., 46, 3163–3171.

© Woodhead Publishing Limited, 2012

Gas chromatography and mass spectroscopy techniques MARTI-CID, R., LLOBET, J. M., CASTELL, V.

59

and DOMINGO, J. L. (2008b), ‘Human dietary exposure to hexachlorobenzene in Catalonia, Spain’, J. Food Protect., 71, 2148–2152. MASTOVSKA, K., DORWEILER, K. J., LEHOTAY, S. J., WEGSCHEID, J. S. and SZPYLKA, K. A. (2010), ‘Pesticide multiresidue analysis in cereal grains using modified QuEChERS method combined with automated direct sample introduction GC-TOFMS and UPLC-MS/MS techniques’, J. Agric. Food Chem., 58, 5959–5972. MATEUS, D., FERREIRA, I. M. P. L. and PINHO, O. (2011), ‘Headspace SPME-GC/MS evaluation of ethanol retention in cooked meals containing alcoholic drinks’, Food Chemistry, 126, 1387–1392. MAWUSSI, G., SANDA, K., MERLINA, G. and PINELLI, E. (2009), ‘Assessment of average exposure to organochlorine pesticides in southern Togo from water, maize (Zea mays) and cowpea (Vigna unguiculata)’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 26, 348–354. MENOTTA, S., D’ANTONIO, M., DIEGOLI, G., MONTELLA, L., RACCANELLI, S. and FEDRIZZI, G. (2010), ‘Depletion study of PCDD/Fs and dioxin-like PCBs concentrations in contaminated home-produced eggs: preliminary study’, Analytica Chimica Acta, 672, 50–54. MEZCUA, M., FERRER, C., GARCIA-REYES, J. F., MARTINEZ-BUENO, M. J., SIGRIST, M. and FERNANDEZ-ALBA, A. R. (2009), ‘Analyses of selected non-authorized insecticides in peppers by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry’, Food Chemistry, 112, 221–225. MORRISSEY, J. A., BLEACKLEY, D. S., WARNER, N. A. and WONG, C. S. (2007), ‘Enantiomer fractions of polychlorinated biphenyls in three selected Standard Reference Materials’, Chemosphere, 66, 326–331. PAKADE, Y. B. and TEWARY, D. K. (2010), ‘Development and applications of single-drop microextraction for pesticide residue analysis: a review’, J. Sep. Sci., 33, 3683–3691. PARR, M. K., OPFERMANN, G. and SCHANZER, W. (2009), ‘Analytical methods for the detection of clenbuterol’, Bioanalysis, 1, 437–450. PASEIRO-CERRATO, R., DE QUIROS, A. R. B., SENDON, R., BUSTOS, J., SANTILLANA, M. I. et al. (2010), ‘Chromatographic methods for the determination of polyfunctional amines and related compounds used as monomers and additives in food packaging materials: a stateof-the-art review’, Comp. Rev. Food Sci. Food Safety, 9, 676–694. PICO, Y. and BARCELO, D. (2008), ‘The expanding role of LC-MS in analyzing metabolites and degradation products of food contaminants’, TrAC Trends Anal. Chem., 27, 821–835. PLAZA-BOLAÑOS, P., FRENICH, A. G. and VIDAL, J. L. M. (2010), ‘Polycyclic aromatic hydrocarbons in food and beverages. Analytical methods and trends’, J. Chromatogr. A, 1217, 6303–6326. PRESTES, O. D., FRIGGI, C. A., ADAIME, M. B. and ZANELLA, R. (2009), ‘Quechers – a modern sample preparation method for pesticide multiresidue determination in food by chromatographic methods coupled to mass spectrometry’, Quimica Nova, 32, 1620–1634. PRIETO, A., BASAURI, O., RODIL, R., USOBIAGA, A., FERNANDEZ, L. A. et al. (2010), ‘Stir-bar sorptive extraction: A view on method optimisation, novel applications, limitations and potential solutions’, J. Chromatogr. A, 1217, 2642–2666. RASTKARI, N., AHMADKHANIHA, R., YUNESIAN, M., BALEH, L. J. and MESDAGHINIA, A. (2010), ‘Sensitive determination of bisphenol A and bisphenol F in canned food using a solidphase microextraction fibre coated with single-walled carbon nanotubes before GC/ MS’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 27, 1460–1468. RATEL, J. and ENGEL, E. (2009), ‘Determination of benzenic and halogenated volatile organic compounds in animal-derived food products by one-dimensional and comprehensive two-dimensional gas chromatography-mass spectrometry’, J. Chromatogr. A, 1216, 7889–7898.

© Woodhead Publishing Limited, 2012

60

Chemical contaminants and residues in food

RAVINDRA, K., DIRTU, A. C.

and COVACI, A. (2008), ‘Low-pressure gas chromatography: Recent trends and developments’, TrAC Trends Anal. Chem., 27, 291–303. RIDGWAY, K., LALLJIE, S. P. D. and SMITH, R. M. (2007), ‘Sample preparation techniques for the determination of trace residues and contaminants in foods’, J. Chromatogr. A, 1153, 36–53. ROBERTS, D., CREWS, C., GRUNDY, H., MILLS, C. and MATTHEWS, W. (2008), ‘Effect of consumer cooking on furan in convenience foods’, Food Addit. Contam., 25, 25–31. RUIZ, E., SANTILLANA, M. I., NIETO, M. T., CIRUGEDA, M. E. and SANCHEZ, J. J. (2010), ‘Determination of furan in jarred baby food purchased from the Spanish market by headspace gas chromatography-mass spectrometry (HS-GC-MS)’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 27, 1208–1214. SANDRA, P., DAVID, F. and VANHOENACKER, G. (2008), ‘Advanced sample preparation techniques for the analysis of food contaminants and residues’, in P. Yolanda, ed., Comprehensive Analytical Chemistry, Food Contaminants and Residue Analysis, Volume 51, Elsevier, Amsterdam, pp. 131–174. SANTINI, A., FERRACANE, R., MECA, G. and RITIENI, A. (2009), ‘Overview of analytical methods for beauvericin and fusaproliferin in food matrices’, Anal. Bioanal. Chem., 395, 1253–1260. SERRANO, R., BARREDA, M. and BLANES, M. A. (2008a), ‘Investigating the presence of organochlorine pesticides and polychlorinated biphenyls in wild and farmed gilthead sea bream (Sparus aurata) from the Western Mediterranean sea’, Mar. Pollut. Bull., 56, 963–972. SERRANO, R., BLANES, M. A. and LOPEZ, F. J. (2008b), ‘Biomagnification of organochlorine pollutants in farmed and wild gilthead sea bream (Sparus aurata) and stable isotope characterization of the trophic chains’, Sci. Total Environ., 389, 340–349. SHARMA, D., NAGPAL, A., PAKADE, Y. B. and KATNORIA, J. K. (2010), ‘Analytical methods for estimation of organophosphorus pesticide residues in fruits and vegetables: a review’, Talanta, 82, 1077–1089. STAJNBAHER, D. and ZUPANCIC-KRALJ, L. (2008), ‘Optimisation of programmable temperature vaporizer-based large volume injection for determination of pesticide residues in fruits and vegetables using gas chromatography-mass spectrometry’, J. Chromatogr. A, 1190, 316–326. TADEO, J. L., SANCHEZ-BRUNETE, C., ALBERO, B. and GARCIA-VALCARCEL, A. I. (2010), ‘Application of ultrasound-assisted extraction to the determination of contaminants in food and soil samples’, J. Chromatogr. A, 1217, 2415–2440. TEO, C. C., TAN, S. N., YONG, J. W. H., HEW, C. S. and ONG, E. S. (2010), ‘Pressurized hot water extraction (PHWE)’, J. Chromatogr. A, 1217, 2484–2494. TOLEDANO, R. M., CORTES, J. M., ANDINI, J. C., VILLEN, J. and VAZQUEZ, A. (2010), ‘Large volume injection of water in gas chromatography-mass spectrometry using the Through Oven Transfer Adsorption Desorption interface: application to multiresidue analysis of pesticides’, J. Chromatogr. A, 1217, 4738–4742. TYAN, Y. C., YANG, M. H., JONG, S. B., WANG, C. K. and SHIEA, J. (2009), ‘Melamine contamination’, Anal. Bioanal. Chem., 395, 729–735. TZING, S. H. and DING, W. H. (2010), ‘Determination of melamine and cyanuric acid in powdered milk using injection-port derivatization and gas chromatographytandem mass spectrometry with furan chemical ionization’, J. Chromatogr. A, 1217, 6267–6273. VAN DER LEE, M. K., VAN DER WEG, G., TRAAG, W. A. and MOL, H. G. J. (2008), ‘Qualitative screening and quantitative determination of pesticides and contaminants in animal feed using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry’, J. Chromatogr. A, 1186, 325–339. VIDAL, J. L. M., PLAZA-BOLANOS, P., ROMERO-GONZALEZ, R. and FRENICH, A. G. (2009), ‘Determination of pesticide transformation products: a review of extraction and detection methods’, J. Chromatogr. A, 1216, 6767–6788.

© Woodhead Publishing Limited, 2012

Gas chromatography and mass spectroscopy techniques VIÑAS, P., MARTINEZ-CASTILLO, N., CAMPILLO, N.

61

and HERNANDEZ-CORDOBA, M. (2011), ‘Directly suspended droplet microextraction with injection-port derivatization coupled to gas chromatography-mass spectrometry for the analysis of polyphenols in herbal infusions, fruits and functional foods’, J. Chromatogr. A, 1218, 639–646. VONDERHEIDE, A. P. (2009), ‘A review of the challenges in the chemical analysis of the polybrominated diphenyl ethers’, Microchem. J., 92, 49–57. VRANOVA, J. and CIESAROVA, Z. (2009), ‘Furan in food – a review’, Czech J. Food Sci., 27, 1–10. WALORCZYK, S. (2008), ‘Application of gas chromatography/tandem quadrupole mass spectrometry to the multi-residue analysis of pesticides in green leafy vegetables’, Rapid Commun. Mass Sp. 22, 3791–3801. WEBER, J. V. and SHARYPOV, V. I. (2009), ‘Ethyl carbamate in foods and beverages: a review’, Environ. Chem. Lett., 7, 233–247. WENZL, T., LACHENMEIER, D. W. and GOKMEN, V. (2007), ‘Analysis of heat-induced contaminants (acrylamide, chloropropanols and furan) in carbohydrate-rich food’, Anal. Bioanal. Chem., 389, 119–137. WRETLING, S., ERIKSSON, A., ESKHULT, G. A. and LARSSON, B. (2010), ‘Polycyclic aromatic hydrocarbons (PAHs) in Swedish smoked meat and fish’, J. Food Compos. Anal., 23, 264–272. WRIGHT, C. (2009), ‘Analytical methods for monitoring contaminants in food – an industrial perspective’, J. Chromatogr. A, 1216, 316–319. ZELINKOVA, Z., NOVOTNY, O., SCHUREK, J., VELISEK, J., HAJSLOVA, J. and DOLEZAL, M. (2008), ‘Occurrence of 3-MCPD fatty acid esters in human breast milk’, Food Addit. Contam. Part A – Chemistry Analysis Control Exposure & Risk Assessment, 25, 669–676.

© Woodhead Publishing Limited, 2012