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ION EXCHANGE | Ion Chromatography Applications
460 ION EXCHANGE / Ion Chromatography Applications
detection. In inorganic analysis, postcolumn derivatization is used to detect and measure ions of transition metals and lanthanides. Reagents used for this purpose are 4-(2-pyridylazo)resorcinol, and the ‘Arsenazo’ dyes. They give products that absorb strongly in the visible region. See also: Amperometry. Carbohydrates: Sugars – Chromatographic Methods. Derivatization of Analytes. Electrophoresis: Principles. Flow Injection Analysis: Principles. Ion Exchange: Principles. Liquid Chromatography: Column Technology; Chiral Analysis of Amino Acids. Sensors: Amperometric Oxygen Sensors.
Further Reading Buchberger WW and Haddad PR (1997) Advances in detection techniques for ion chromatography. Journal of Chromatography 789: 67–83. Fritz JS and Gjerde DT (2000) Ion Chromatography, 3rd edn. Heidelberg and New York: Huethig. Haddad PR (2001) Ion chromatography retrospectivity. Analytical Chemistry 73: 266A–273A. Haddad PR, Jackson PE, and Shaw MJ (2003) Development in suppressor technology for inorganic ion analysis by ion chromatography using conductivity detection. Journal of Chromatography A 1000: 725–742.
Lee HJ and Girault HH (1998) Amperometric ion detector for ion chromatography. Analytical Chemistry 70: 4280– 4285. Lopez-Ruiz B (2000) Advances in the determination of inorganic anions by ion chromatography. Journal of Chromatography A 881: 607–627. Lucy CA (2003) Evolution of ion-exchange: From Moses to the Manhattan project to Modern Times. Journal of Chromatography A 1000: 711–724. Nesterenko PN (2001) Simultaneous separation and detection of anions and cations in ion chromatography. Trends in Analytical Chemistry 20: 311–319. Pietrzyk DJ (1998) Ion chromatography by HPLC. Chromatographic Science Series 78: 413–462. Saari-Nordhaus R and Anderson JM (2002) Recent advances in ion chromatography suppressor improve anion separation and detection. Journal of Chromatography A 956: 15–22. Sarzanini C (2002) Recent developments in ion chromatography (review). Journal of Chromatography A 956: 3–14. Stevens TS (2002) The membrane suppressor: A historical perspective (review). Journal of Chromatography A 956: 43–46. Viehweger KH (ed.) (2000) Practical Ion Chromatography: An Introduction. Metrohm: Herisau, Switzerland. Weiss J (2001) Ion Chromatography, 3rd edn. New York: Wiley-VCH. Yuan JP and Chen F (2001) Indirect photometric ion chromatographic analysis. Biotechnology Letters 23: 757–760.
Ion Chromatography Applications B Paull, Dublin City University, Dublin, Republic of Ireland & 2005, Elsevier Ltd. All Rights Reserved.
Introduction When first developed, ion chromatography (IC) was based on the use of a low-capacity anion exchange separator column used with a basic eluent and a suppressor column, with conductimetric detection. This allowed the sensitive detection of a limited number of inorganic anions in aqueous samples in reasonably short analysis times. Later work saw the introduction of nonsuppressed IC, which utilized low-conductivity eluents, mainly organic aromatic weak acids, that could be used without a suppressor module, thus simplifying the chromatographic system. Nonsuppressed IC, being less sensitive than suppressed IC, was generally more applied to
samples containing higher solute concentrations. Improvements in stationary-phase technology led to more efficient simultaneous separations of inorganic and organic anions, and combined with the development of improved suppressor systems, such as selfregenerating membrane suppressors, this saw IC establish itself as the method of choice for anion analysis of aqueous samples. In the application of IC to the determination of organic and inorganic cations, there has also been much progress. Again, both suppressed and nonsuppressed IC systems have been used, predominantly for the determination of alkali and alkaline earth metal ions and organic amines, again mostly in aqueous-based sample matrices. The following is a simple review of some of the more interesting applications of IC, focusing on those applications based on the use of ion exchange stationary phases, although alternative approaches to the separation of ionic species, such as ion interaction liquid chromatography, will also be included.
ION EXCHANGE / Ion Chromatography Applications 461
Environmental Applications Natural Waters
Inorganic anions One of the commonest applications of IC is the analysis of natural nonsaline water samples, such as subsurface waters, spring waters, steams, river waters, and lakes. Particular interest lies in the use of IC as a laboratory-based technique for the routine monitoring of the above sample types for nutrient anion concentrations, such as nitrates, nitrites, sulfates, and phosphates. In most cases suppressed IC is used, due to its ability to quantify the above species, which are often present at submmol l 1 concentrations. The US EPA Method 300 (Determination of fluoride, chloride, nitrite, nitrate, phosphate, and sulfate in water samples by IC) describes suitable conditions for this particular application, based on the use of a Dionex IonPac AS4A anion exchange column, with a carbonate/bicarbonate eluent (or a similar stationary-phase/eluent combination that produces similar or better selectivity and efficiency) and suppressed conductivity detection. Utilizing these conditions, resolution of the above anions from each other and matrix anions, typically chloride, is possible. Approximate linear ranges quoted for the above anions, using a similar analytical setup to that described above, are between 0.01 and 5 mmol 1, with detection limits in the order of 0.1–1 mmol l 1. Similar detection limits for nitrate and nitrite can be achieved using IC combined with direct UV absorbance detection at 225 nm. In this case large matrix peaks resulting from excess sulfate and chloride are essentially eliminated due to their UV transparency at this wavelength. With IC applications utilizing direct UV detection, the eluting anion within the mobile phase must also be UV transparent if sensitive detection is to be obtained. Nonsuppressed IC methods for natural water samples are generally 1–2 orders of magnitude less sensitive for common inorganic anions than suppressed conductivity methods, but still find useful application for the determination of higher-concentration matrix anions, such as chloride and sulfate. Typical eluents used include p-hydroxybenzoic acid or phthalic acid, often used with small amounts of organic solvent to improve peak shapes. Such eluents can also be employed for indirect UV detection, although again sensitivity is somewhat less than for direct UV detection. The determination of the above nutrient anions in natural saline samples, such as coastal seawaters, is also of interest to environmental scientists, and several IC methods have been developed that can tolerate the high salt content of such samples. Column switching techniques have been used for this type of application.
Saline samples are injected onto short high-capacity anion exchange guard columns, which are separated from the main analytical anion exchange column by a switching valve. Correct timing of the switching valve allows the early eluting excess chloride to be directed to waste before the more retained anions of interest, such as bromide, phosphate, sulfate, nitrite, nitrate, and residual chloride, are eluted. Redirecting the later eluting anions onto the analytical column allows separation and detection to take place and eliminates large-matrix chloride peaks. An alternative approach is to include the matrix anion in the eluent itself, so-called ‘matrix elimination IC’. Here a sodium chloride eluent is used with a strong anion exchange column, thus eliminating any ‘self-elution’ problems when analyzing saline samples. The method is most suitable for strongly retained anions such as iodide, and has indeed been used for the determination of this particular anion in seawater samples, with trace level detection made possible through postcolumn reaction and visible absorbance detection. Inorganic cations For the determination of common inorganic cations in nonsaline natural waters, IC competes with atomic spectroscopy as the method of choice. Despite this, IC is used by many monitoring agencies for the determination of alkali and alkaline earth metal cations and, to a lesser extent, selected transition metal cations. Two approaches are commonly taken. Firstly, for the determination of alkali metal ions, a strong cation exchanger (sulfonated) is generally used with a strong acid eluent and combined with suppressed conductivity detection. For the simultaneous determination of alkali and alkaline earth metal ions, a weaker cation exchanger (carboxylated or carboxylated and phosphonated, e.g., a Dionex IonPac CS12A column) is more suitable, and used with a weaker eluent and either suppressed conductivity detection or indirect conductivity detection. Such a system allows the simultaneous determination of lithium, sodium, ammonia, potassium, magnesium, and calcium in water samples (EPA Method 300.7). Treated Waters
Treated waters for domestic use are routinely analyzed using IC for both naturally present common inorganic anions and trace anionic contaminants, several classes of which actually originate as by-products of the treatment processes themselves. Oxyhalides, which originate from various drinking water disinfection processes, such as chlorination and ozonation, can be found present in finished drinking
462 ION EXCHANGE / Ion Chromatography Applications
waters and require monitoring at sub-micromolar concentrations. For example, chlorate and chlorite can result from treatment with chlorine dioxide, and bromate and iodate can be formed from the treatment of bromide- and iodide-containing drinking waters with ozonation. The 1998 European Drinking Water Directive set a mandatory standard limit of 10 mg l 1 for bromate in drinking water to be in place by 2008, necessitating sensitive analytical methods for this particular analyte to be developed. When using IC for the determination of bromate in drinking water, a high-capacity anion exchange column is generally used to allow the injection of larger sample volumes, thus improving detection limits. Detection of ultratrace levels of bromate is achieved via postcolumn reaction, followed by visible detection (450 nm), using o-dianisidine dihydrochloride (as in EPA Method 317.0). Alternative detection can be achieved via postcolumn reaction with potassium iodide–ammonium heptamolybdate (triiodide method), although both methods result in a similar sensitivity for bromate with detection limits of B0.5 mg l 1. Figure 1 shows an ion chromatograph of a mixture of common inorganic anions and trace oxyhalides, here using only suppressed conductivity detection (obtained using EPA Method 300.1, Part B).
1
4
8
10
Two compounds that are currently generating much concern are azide and perchlorate, salts of which are currently used in the explosives and pyrotechnics industry, with perchlorate also used as a primary oxidant in solid rocket fuel. IC can be used for the monitoring of both analytes in natural and treated waters. For perchlorate, EPA Method 314.0 (Determination of perchlorate in drinking water by ion chromatography) has been developed, which suggests the use of a Dionex IonPac AS16 anion exchange column (or equivalent) with a 35 mM NaOH eluent and suppressed conductivity detection. Finally, there has also been much interest in recent years in the contamination of groundwater, well water, and drinking water supplies with hexavalent chromium. An EPA method has been developed utilizing IC for hexavalent chromium determinations (EPA Method 218.6). This method specifies the use of a high-capacity Dionex IonPac AS7 anion exchange column and UV/Vis detection following postcolumn reaction with diphenylcarbazine. Figure 2 shows an ion chromatogram of a spiked and unspiked drinking water sample obtained using a modified version of EPA Method 218.6. Table 1 lists some of the IC methods prescribed by the US EPA for the analysis of drinking water including several oxyhalide disinfection by-products (DBPs). Note how inductively coupled plasma mass spectrometry (ICP-MS) is also used for bromate detection in Method 321.8.
3.0 µS
0.002 (A) Chromate
AU
Chromate (B)
2
5
3 0
4
8
67
12 16 Time (min)
9 20
24
Figure 1 Chromatogram of 10 inorganic anions and oxyhalides in a water sample using suppressed ion chromatography. Peak identification: 1 ¼ fluoride, 2 ¼ chlorite, 3 ¼ bromate, 4 ¼ chloride, 5 ¼ nitrite, 6 ¼ bromide, 7 ¼ chlorate, 8 ¼ nitrate, 9 ¼ phosphate, 10 ¼ sulfate. (Reprinted with permission from Saari-Nordhaus R and Anderson JM Jr. (2002) Recent advances in ion chromatography suppressor improve anion separation and detection. Journal of Chromatography A 956: 15–22; & Elsevier.)
0 0
2
4 Time (min)
6
8
Figure 2 Ion chromatograms of chromate in drinking waters: (A) unspiked sample, (B) sample spiked with 0.2 mg l 1 Cr(VI). (Reprinted with permission from Thomas DH, Rohrer JS, Jackson PE, Pak T, and Scott JN (2002) Determination of hexavalent chromium at the level of California public health goal by ion chromatography. Journal of Chromatography A 956: 255–259; & Elsevier.)
ION EXCHANGE / Ion Chromatography Applications 463 Table 1 EPA IC methods for drinking water analysis EPA method
Analysis
Method 300.1
Determination of inorganic anions and oxyhalides in drinking water by IC
Method 300.7
Determination of inorganic cations in drinking water by IC
Method 314.0
Determination of perchlorate in drinking water by IC
Method 317.0
Determination of inorganic oxyhalide disinfection by-products in drinking water using IC with the addition of a postcolumn reagent for trace bromate analysis
Rev. 2.0 Method 218.6
Determination of dissolved hexavalent chromium in drinking water, groundwater, and industrial wastewater effluents by IC
EPA Method 321.8
Determination of bromate in drinking waters by IC with ICP-MS detection
EPA Method 326.0
Determination of inorganic oxyhalide disinfection by-products in drinking water using IC incorporating the addition of a suppressor acidified postcolumn reagent for trace bromate analysis
Soil Analysis
Inorganic anions IC is used extensively for the determination of common inorganic anions in soil extracts. The key to valuable data when carrying out such analyses is the use of correct and reproducible extraction methods. For the determination of inorganic anions, often the soil is simply extracted using water. Such an application of IC is used to provide information on the fate of nutrient anions resulting from agricultural practices and to determine soil nutrient retention and leaching rates. Organic anions Both anion exchange chromatography and ion exclusion chromatography have been used extensively for the determination of low-molecular-weight organic acids in soil extracts. Malic acid, malonic acid, maleic acid, succinic acid, fumaric acid, ascorbic acid, citric acid, isocitric acid, succinic acid, tartaric acid, oxalic acid, and glycolic acid can all be determined using these techniques. Inorganic cations For the extraction of cations from soils, a number of approaches are used, dependent on whether the analyst wishes to determine labile or nonlabile cation concentrations. Extractions can be carried out using simply water or electrolyte solutions, or strong acid solutions for nonlabile cations. In this way, IC can also be used to determine the ion exchange capacity of the soils in question. Recently, IC has also found increased application in the field of metal speciation. Short anion exchange columns have been used for the rapid separation of anionic species of arsenic, selenium, and chromium,
extracted from contaminated soils, and followed by elemental specific detection. Atmospheric Samples
The determination of ambient concentrations of gaseous nitrogen- and sulfur-containing species (predominantly nitrate and sulfate) in the atmosphere has also been carried out using IC after collection using passive samplers. Wet denuder systems have also been developed for the collection of soluble ionogenic trace gases and soluble ionic species adsorbed onto atmospheric particles, used on-line with IC for continuous monitoring purposes. The use of large-volume filter-based samplers for the collection of atmospheric particulates has also been combined with IC for the determination of absorbed metal species. Collected samples are extracted from the filters and desorbed from the particulate matter using acidic solutions prior to analysis by IC combined with elemental selective detection such as ICP-MS. Hexavalent chromium, platinum, and palladium have been determined in this way, as have many other transition and heavy metal ions. Rainwater Automated rainwater collectors have been used in combination with IC for the determination of low-level concentrations of dissolved inorganic anions or cations. Due to the ‘clean’ nature of the sample, online preconcentration of the analytes can be readily achieved using short ion exchange preconcentrator cartridges onto which large sample volumes can be loaded, prior to elution onto the appropriate separator ion exchange column. This approach is used for the ultratrace analysis of rainwater samples.
464 ION EXCHANGE / Ion Chromatography Applications Table 2 Examples of foodstuffs to which IC has been applied for anion determinations following appropriate extraction methods Anions
Sample matrix
Nitrate, nitrite, sulfate, phosphate, chloride Fluoride Iodide Sulfite Bromide Chlorite and chlorate Bromate Iodate Chromate Selenite and selenate Arsenite and arsenate Cyanide
Milk products, fruits and fruit juices, beverages and alcoholic products, meat products, bakery products, vegetables, cereals As above plus citrus fruits and leaves and spinach Seafood, food colorings, and iodized table salt Beer, lemon juice, potatoes, seafood, fruits (grapes) Milk, food colorings, rice products, bakery products Vegetables Bakery products Iodized table salt Orange juice, potato products Vegetables, cereals, orange juice Food supplements, cereals, vegetables Fruits and fruit juices
An alternative approach has been developed based on a weakly acidic cation exchange column, used with a dilute tartaric acid/crown ether eluent, which resulted in the ability to separate both inorganic anions (chloride, nitrate, and sulfate) and inorganic cations (sodium, potassium, ammonium, calcium, and magnesium) simultaneously in real rainwater samples. The anions were retained through an ion exclusion mechanism and the cations were retained through a simple cation exchange mechanism. Sensitive detection was achieved using direct conductivity.
Industrial Applications Food and Beverages
As with most chromatographic methods applied to solid samples, sample digestion and analyte extraction methods are all important. IC is finding application in the analysis of foodstuffs following sample preparation using such techniques as microwave digestion, supercritical fluid extraction, accelerated solvent extraction, and pyrohydrolysis. Inorganic anions The predominant anionic species determined in foodstuffs are once again the nitrogen-, sulfur-, and phosphorus-containing species, as well as the halide ions. Table 2 lists some inorganic anions and some of the foodstuffs that have been analyzed for these anions using IC. Some of the more important applications in food analysis include nitrates and nitrites in baby food products, excess of which can lead to induce methemoglobinemia (blue baby syndrome), and the monitoring of sulfite, which is added to many foodstuffs as a preservative and to bleach food starches, and is only recently being linked to serious health effects. Also, residual bromate can be monitored in bakery products from the continuing use of bromate salts as dough conditioners.
Organic acids In beverages such as wines, beers, and fruit juices, IC has also been widely applied in the determination of various organic acids, although in many cases ion exclusion chromatography is often used in preference to anion exchange. Sugars In the brewing industry, IC is used for the determination and monitoring of fermentable sugars, such as glucose, fructose, isomaltose, sucrose, maltose, maltotriose, and numerous others. For sensitive detection, pulsed amperometric detection is often preferred. Inorganic and organic cations In the analysis of foodstuff extracts and digests, IC has been predominantly applied to the determination of alkali and alkaline earth metal ions and, to a lesser extent, selected organic amines. Alkali and alkaline earth metal ions are naturally present in most foodstuffs, although accurate monitoring is still necessary to evaluate nutritional values, e.g., the sodium or calcium content of foodstuffs. As mentioned previously, ammonium content can also be determined using IC simultaneously with alkali metal ions, and is often used as an indicator of food quality. Transition and heavy metal ions have also been determined in foodstuffs using IC, particularly seafood, where heavy metal contamination with metals such as cadmium and lead is often a problem. After separation using cation exchange or ion interaction chromatography, sensitive detection is generally achieved using postcolumn reaction detection with a suitable color-forming ligand, such as 4-(2-pyridylazo) resorcinol (PAR). Other metals such as zinc, copper, iron, cobalt, nickel, chromium, and manganese can also be detected in this way. In an interesting recent application, the determination of acrylamide in foodstuffs has been shown using accelerated solvent extraction followed by IC
ION EXCHANGE / Ion Chromatography Applications 465
with either UV or MS detection. Extracted samples can be analyzed directly using IC, with limits of determination of 50 ng per g acrylamide in foodstuffs possible using MS detection with single ion monitoring (SIM) at m/z 72. Pharmaceuticals
In the preparation of pharmaceutical products, the purity of reagents is of utmost importance. IC is often used for trace anion and cation determinations in starting materials, the simplest of which is reagent grade water. However, actual pharmaceutical preparations are often complex mixtures and IC provides alternative column selectivity to standard reversedphase HPLC, and is often more suited for the separation of very polar organics commonly used in pharmaceutical products. Table 3 lists some of the organic species that have been determined using IC. Often for such analytes UV absorbance is the preferred mode of detection, provided the analyte contains a suitable chromophore.
sodium, chloride, and sulfate on a near-real-time basis, and can also differentiate among different oxidation states of ions such as nitrate, nitrite, sulfate, and thiosulfate. These oxidation states respond to the general oxidizing tendency of coolant waters, which is an important variable in controlling localized corrosion. Some impressive recent applications of IC within this industry include: the determination of mono-, di-, and tributyl phosphates, the latter of which is an important compound used in the area of nuclear fuel reprocessing; the determination of long-lived artificial radionuclides resulting from fission reactions using IC coupled to ICP-MS detection; the use of IC to determine amines in amine-dosed feedwater used for erosion control in boiler tubes; and the application of IC to the determination of transition metal cations in the primary coolants of light water reactors. Figure 3 shows an ion chromatograph of a condensate discharge water sample from a fossil fuel power station containing trace amounts of inorganic anions and organic acids.
Nuclear and Fossil Fuel Power Generation Industry
As with the pharmaceutical products above, there is also great concern over contamination problems in the power generation industry. IC is extensively used to determine ultratrace concentrations of ionic species in process waters, coolant waters, wastewater, and other waste materials. The popularity of the technique is due to IC being one of a few analytical technologies that is able to measure ng per g concentrations of potentially corrosive ions such as
Semiconductor Industry
The semiconductor industry utilizes IC to monitor and identify the possible contamination of products during manufacture. Much of the application of IC is to trace inorganic anion analysis and, to a lesser extent, trace alkali and alkaline earth cation determinations. The sample matrices that are monitored using IC in the semiconductor industry include the large variety of chemicals used for cleaning,
Table 3 Examples of pharmaceutical preparations to which IC has been applied Analytes
Sample matrix
Column
Detection method
Citrate Saccharin aspartane, acesulfame-k, benzoate, sorbate, caffeine, theobromine, theophylline Trifluoroacetate Alenalol, metaprolol, alprenolol, oxprenolol, acebutolol, propanolol Paracetamol, salicylate Alkyl sulfonic acids Alendronate
Liquid and tablet formulations Tablet preparations
Anion exchange Anion exchange
Indirect UV absorbance Tunable UV absorbance
Cell-based products b-Blocker tablet preparations
Anion exchange Anion exchange
Suppressed conductivity Tunable UV absorbance
Tablet preparations Sulfonated sugar preparations Dosage formulations
Anion exchange Anion exchange Anion exchange
Injection formulations
Cation exchange
UV absorbance Suppressed conductivity Electrospray mass spectrometry Nonsuppressed conductivity
Antibiotic preparations Hypocholesterolemic agent preparations
Cation exchange Cation exchange
UV absorbance Nonsuppressed conductivity
Catecholamines (norepinephrine, epinephrine, dopamine) Tetracyclines Amylamine, t-butylamine
466 ION EXCHANGE / Ion Chromatography Applications
help in the diagnosis of lactic acidosis in diabetic patients.
0.75 6
7
3 µS 5 4 2
8
1
9
10
11
0.15 10
20 Retention time (min)
30
Figure 3 Ion chromatogram of a condensate discharge water sample. Peak identification: 1 ¼ fluoride, 2 ¼ acetate, 3 ¼ formate, 4 ¼ chloride, 5 ¼ nitrite, 6 ¼ carbonate, 7 ¼ sulfate, 8 ¼ unknown, 9 ¼ nitrate, 10 ¼ unknown, 11 ¼ phosphate. (Reprinted with permission from Lu Z, Liu Y, Barreto V, et al. (2002) Determination of anions at trace levels in power plant water samples by ion chromatography with electrolytic eluent generation and suppression. Journal of Chromatography A 956: 129–138; & Elsevier.)
washing, polishing, and treating surfaces, such as reagent water, solvents, strong acids and bases, and oxidizing agents. Process gases and clean room gases, and filtered air are also monitored.
Biological Applications Analysis of Blood, Plasma, and Serum
The ability to determine quantitatively certain ionic analytes in blood, plasma, and serum samples can be of substantial benefit to those attempting the diagnosis of certain diseases, particularly where concentrations of these analytes are known to be directly related to specific physiological disorders. Anions IC has established itself as the method of choice for the determination of common anions such as chloride, sulfate, and phosphate in blood and serum samples. For example, a common clinical application of IC is the study of sulfa drug metabolism through the monitoring of blood sulfate levels. Samples are generally pretreated using ultrafiltration or acidification and centrifugation, or both. Both IC and ion exclusion chromatography have been applied to the determination of bicarbonate in blood plasma. Ion exclusion has also been extensively applied to the determination of certain organic acids in blood plasma, such as pyruvate and lactate, the latter of which is used to
Cations There have been many applications of IC to the determination of sodium, potassium, and ammonium in blood serum. In most cases, serum samples were simply ultrafiltered and injected directly. In other cases only dilution was necessary. Total and free concentrations of calcium and magnesium in blood serum can also be determined using IC. Total concentrations can be determined using sample acidification followed by centrifugation. Free concentrations of the cations can be determined after passage of the untreated sample through a cation exchange solid-phase extraction (SPE) cartridge to trap the cations and isolate them from those ions bound to serum proteins. Analysis of Urine
As with blood, urine analysis is used in clinical studies, and the relative concentrations of various ionic species are of great importance in both disease diagnostic and drug metabolism studies. For example, IC is used to determine urine oxalate concentrations. Urinary oxalate levels are an important parameter in urolithiasis research (kidney stones). Other anions that can be determined in urine using IC include phosphate, sulfate, bromide, citrate, nitrate, nitrite, and thiosulfate. As with blood and serum samples, both ultrafiltration and centrifugation are often used as sample cleanup steps. Interesting applications include the use of IC coupled with ICP-MS detection for the determination of anionic arsenic species in urine resulting from occupational and dietary exposure. Species include urinary arsenate, arsenite, dimethylarsinic acid, and methylarsonic acid, and are separated using a hydrophilic anion exchange resin with a weak acid eluent. Studies have also been carried out using IC and ion interaction liquid chromatography to determine human urinary thiocyanate concentrations and relate concentrations found to levels of smoking. Thiocyanate is the main metabolic product of cyanide inhaled with cigarette smoke. Figure 4 shows overlaid ion chromatograms of a smoker’s urine sample and the same sample spiked with thiocyanate. The chromatograms shown were obtained using ion interaction chromatography, utilizing a short reversedphase column and a tetrabutylammonium chloride and methanol eluent. Detection was carried out using direct UV absorbance at 230 nm. Analysis of Saliva and Sweat
Finally, IC methods have been applied to the determination of both inorganic anions and alkali and
Response (AU)
ION EXCHANGE / Chelation Ion Chromatography 0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0
467
See also: Ion Exchange: Overview; Principles; Ion Chromatography Instrumentation; Chelation Ion Chromatography; Isolation of Biopolymers; Isotope Separation. Thiocyanate
Further Reading
0
1
2
3
4
5
6
7
8
9
10
Time (min) Figure 4 Analysis of urine for thiocyanate using ion interaction liquid chromatography. Lower trace: sample (heavy smoker) diluted 1:20. Upper trace (heavy smoker) diluted 1:20 and spiked with thiocyanate.
alkaline earth cations in saliva. The sample matrix is relatively simple compared to other biological fluids and can be analyzed directly or simply diluted prior to injection. IC methods have also been developed for the determination of sweat samples for ionic analytes. Methods looking at sulfate levels and also concentrations of sodium and potassium in sweat samples have been developed, with relative levels of the latter metal ions being useful indicators of several important diseases, one of which is cystic fibrosis.
Betti M (1997) Use of ion chromatography for the determination of fission products and actinides in nuclear applications. Journal of Chromatography A 789: 369–379. Buldini PL, Cavalli S, and Trifiro A (1997) State-ofthe-art ion chromatographic determination of inorganic ions in food. Journal of Chromatography A 789: 529–548. Haddad PR and Jackson PE (1990) Ion Chromatography. Principles and Applications. Amsterdam: Elsevier. Lopez-Ruiz B (2000) Advances in the determination of inorganic anions by ion chromatography. Journal of Chromatography A 881: 607–627. Singh RP, Smesko SA, and Abbas NM (1997) Ion chromatographic characterisation of toxic solutions: analysis and ion chemistry of biological liquids. Journal of Chromatography A 774: 21–35. Small H (1990) Ion Chromatography. New York: Plenum. Smith RE (1987) Ion Chromatography Applications. Boca Raton, FL: CRC Press. Vanatta LE (2001) Application of ion chromatography in the semiconductor industry. Trends in Analytical Chemistry 20: 336–345.
Chelation Ion Chromatography P Jones, University of Plymouth, Devon, UK P N Nesterenko, Lomonosov Moscow State University, Moscow, Russia & 2005, Elsevier Ltd. All Rights Reserved.
Introduction It is now over 60 years since the development of column ion-exchange chromatography using polymeric resins. Interestingly, little has changed since then in terms of the basic separation processes for inorganic anions and cations. The renaissance in the 1970s, where ion-exchange was the principal process in a group of techniques now known as ion chromatography (IC), was mainly associated with the improvement in efficiency of stationary phases and detection systems rather than new types of ionexchange groups or elution systems. In essence, the IC separation of metal ions principally involves the use of eluents containing complexing organic acids,
such as tartaric, citric, oxalic, combined with high efficiency stationary phases. The complexing strength of acid and concentration chosen depended on whether the ion-exchange substrate was cationic, anionic, or mixed. Although poly(styrene–divinylbenzene) (PS–DVB) based resins are still the most common substrate, silica-based materials are increasingly being used. There are a number of problems associated with present IC methods involving high efficiency ion-exchange separations of metal ions, the two principal ones being sensitivity to ionic strength and limited selectivity. The influence of ionic strength is particularly serious as a relatively large salt concentration in the sample can drastically affect the chromatography, in many cases making it impossible to resolve the analytes. Limited selectivity is also a restriction, as once the substrate is chosen for conventional ion-exchange separations there are only a small number of cases where changes in eluent composition can significantly alter separation order.
detection. In inorganic analysis, postcolumn derivatization is used to detect and measure ions of transition metals and lanthanides. Reagents used for this purpose are 4-(2-pyridylazo)resorcinol, and the ‘Arsenazo’ dyes. They give products that absorb strongly in the visible region. See also: Amperometry. Carbohydrates: Sugars – Chromatographic Methods. Derivatization of Analytes. Electrophoresis: Principles. Flow Injection Analysis: Principles. Ion Exchange: Principles. Liquid Chromatography: Column Technology; Chiral Analysis of Amino Acids. Sensors: Amperometric Oxygen Sensors.
Further Reading Buchberger WW and Haddad PR (1997) Advances in detection techniques for ion chromatography. Journal of Chromatography 789: 67–83. Fritz JS and Gjerde DT (2000) Ion Chromatography, 3rd edn. Heidelberg and New York: Huethig. Haddad PR (2001) Ion chromatography retrospectivity. Analytical Chemistry 73: 266A–273A. Haddad PR, Jackson PE, and Shaw MJ (2003) Development in suppressor technology for inorganic ion analysis by ion chromatography using conductivity detection. Journal of Chromatography A 1000: 725–742.
Lee HJ and Girault HH (1998) Amperometric ion detector for ion chromatography. Analytical Chemistry 70: 4280– 4285. Lopez-Ruiz B (2000) Advances in the determination of inorganic anions by ion chromatography. Journal of Chromatography A 881: 607–627. Lucy CA (2003) Evolution of ion-exchange: From Moses to the Manhattan project to Modern Times. Journal of Chromatography A 1000: 711–724. Nesterenko PN (2001) Simultaneous separation and detection of anions and cations in ion chromatography. Trends in Analytical Chemistry 20: 311–319. Pietrzyk DJ (1998) Ion chromatography by HPLC. Chromatographic Science Series 78: 413–462. Saari-Nordhaus R and Anderson JM (2002) Recent advances in ion chromatography suppressor improve anion separation and detection. Journal of Chromatography A 956: 15–22. Sarzanini C (2002) Recent developments in ion chromatography (review). Journal of Chromatography A 956: 3–14. Stevens TS (2002) The membrane suppressor: A historical perspective (review). Journal of Chromatography A 956: 43–46. Viehweger KH (ed.) (2000) Practical Ion Chromatography: An Introduction. Metrohm: Herisau, Switzerland. Weiss J (2001) Ion Chromatography, 3rd edn. New York: Wiley-VCH. Yuan JP and Chen F (2001) Indirect photometric ion chromatographic analysis. Biotechnology Letters 23: 757–760.
Ion Chromatography Applications B Paull, Dublin City University, Dublin, Republic of Ireland & 2005, Elsevier Ltd. All Rights Reserved.
Introduction When first developed, ion chromatography (IC) was based on the use of a low-capacity anion exchange separator column used with a basic eluent and a suppressor column, with conductimetric detection. This allowed the sensitive detection of a limited number of inorganic anions in aqueous samples in reasonably short analysis times. Later work saw the introduction of nonsuppressed IC, which utilized low-conductivity eluents, mainly organic aromatic weak acids, that could be used without a suppressor module, thus simplifying the chromatographic system. Nonsuppressed IC, being less sensitive than suppressed IC, was generally more applied to
samples containing higher solute concentrations. Improvements in stationary-phase technology led to more efficient simultaneous separations of inorganic and organic anions, and combined with the development of improved suppressor systems, such as selfregenerating membrane suppressors, this saw IC establish itself as the method of choice for anion analysis of aqueous samples. In the application of IC to the determination of organic and inorganic cations, there has also been much progress. Again, both suppressed and nonsuppressed IC systems have been used, predominantly for the determination of alkali and alkaline earth metal ions and organic amines, again mostly in aqueous-based sample matrices. The following is a simple review of some of the more interesting applications of IC, focusing on those applications based on the use of ion exchange stationary phases, although alternative approaches to the separation of ionic species, such as ion interaction liquid chromatography, will also be included.
ION EXCHANGE / Ion Chromatography Applications 461
Environmental Applications Natural Waters
Inorganic anions One of the commonest applications of IC is the analysis of natural nonsaline water samples, such as subsurface waters, spring waters, steams, river waters, and lakes. Particular interest lies in the use of IC as a laboratory-based technique for the routine monitoring of the above sample types for nutrient anion concentrations, such as nitrates, nitrites, sulfates, and phosphates. In most cases suppressed IC is used, due to its ability to quantify the above species, which are often present at submmol l 1 concentrations. The US EPA Method 300 (Determination of fluoride, chloride, nitrite, nitrate, phosphate, and sulfate in water samples by IC) describes suitable conditions for this particular application, based on the use of a Dionex IonPac AS4A anion exchange column, with a carbonate/bicarbonate eluent (or a similar stationary-phase/eluent combination that produces similar or better selectivity and efficiency) and suppressed conductivity detection. Utilizing these conditions, resolution of the above anions from each other and matrix anions, typically chloride, is possible. Approximate linear ranges quoted for the above anions, using a similar analytical setup to that described above, are between 0.01 and 5 mmol 1, with detection limits in the order of 0.1–1 mmol l 1. Similar detection limits for nitrate and nitrite can be achieved using IC combined with direct UV absorbance detection at 225 nm. In this case large matrix peaks resulting from excess sulfate and chloride are essentially eliminated due to their UV transparency at this wavelength. With IC applications utilizing direct UV detection, the eluting anion within the mobile phase must also be UV transparent if sensitive detection is to be obtained. Nonsuppressed IC methods for natural water samples are generally 1–2 orders of magnitude less sensitive for common inorganic anions than suppressed conductivity methods, but still find useful application for the determination of higher-concentration matrix anions, such as chloride and sulfate. Typical eluents used include p-hydroxybenzoic acid or phthalic acid, often used with small amounts of organic solvent to improve peak shapes. Such eluents can also be employed for indirect UV detection, although again sensitivity is somewhat less than for direct UV detection. The determination of the above nutrient anions in natural saline samples, such as coastal seawaters, is also of interest to environmental scientists, and several IC methods have been developed that can tolerate the high salt content of such samples. Column switching techniques have been used for this type of application.
Saline samples are injected onto short high-capacity anion exchange guard columns, which are separated from the main analytical anion exchange column by a switching valve. Correct timing of the switching valve allows the early eluting excess chloride to be directed to waste before the more retained anions of interest, such as bromide, phosphate, sulfate, nitrite, nitrate, and residual chloride, are eluted. Redirecting the later eluting anions onto the analytical column allows separation and detection to take place and eliminates large-matrix chloride peaks. An alternative approach is to include the matrix anion in the eluent itself, so-called ‘matrix elimination IC’. Here a sodium chloride eluent is used with a strong anion exchange column, thus eliminating any ‘self-elution’ problems when analyzing saline samples. The method is most suitable for strongly retained anions such as iodide, and has indeed been used for the determination of this particular anion in seawater samples, with trace level detection made possible through postcolumn reaction and visible absorbance detection. Inorganic cations For the determination of common inorganic cations in nonsaline natural waters, IC competes with atomic spectroscopy as the method of choice. Despite this, IC is used by many monitoring agencies for the determination of alkali and alkaline earth metal cations and, to a lesser extent, selected transition metal cations. Two approaches are commonly taken. Firstly, for the determination of alkali metal ions, a strong cation exchanger (sulfonated) is generally used with a strong acid eluent and combined with suppressed conductivity detection. For the simultaneous determination of alkali and alkaline earth metal ions, a weaker cation exchanger (carboxylated or carboxylated and phosphonated, e.g., a Dionex IonPac CS12A column) is more suitable, and used with a weaker eluent and either suppressed conductivity detection or indirect conductivity detection. Such a system allows the simultaneous determination of lithium, sodium, ammonia, potassium, magnesium, and calcium in water samples (EPA Method 300.7). Treated Waters
Treated waters for domestic use are routinely analyzed using IC for both naturally present common inorganic anions and trace anionic contaminants, several classes of which actually originate as by-products of the treatment processes themselves. Oxyhalides, which originate from various drinking water disinfection processes, such as chlorination and ozonation, can be found present in finished drinking
462 ION EXCHANGE / Ion Chromatography Applications
waters and require monitoring at sub-micromolar concentrations. For example, chlorate and chlorite can result from treatment with chlorine dioxide, and bromate and iodate can be formed from the treatment of bromide- and iodide-containing drinking waters with ozonation. The 1998 European Drinking Water Directive set a mandatory standard limit of 10 mg l 1 for bromate in drinking water to be in place by 2008, necessitating sensitive analytical methods for this particular analyte to be developed. When using IC for the determination of bromate in drinking water, a high-capacity anion exchange column is generally used to allow the injection of larger sample volumes, thus improving detection limits. Detection of ultratrace levels of bromate is achieved via postcolumn reaction, followed by visible detection (450 nm), using o-dianisidine dihydrochloride (as in EPA Method 317.0). Alternative detection can be achieved via postcolumn reaction with potassium iodide–ammonium heptamolybdate (triiodide method), although both methods result in a similar sensitivity for bromate with detection limits of B0.5 mg l 1. Figure 1 shows an ion chromatograph of a mixture of common inorganic anions and trace oxyhalides, here using only suppressed conductivity detection (obtained using EPA Method 300.1, Part B).
1
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Two compounds that are currently generating much concern are azide and perchlorate, salts of which are currently used in the explosives and pyrotechnics industry, with perchlorate also used as a primary oxidant in solid rocket fuel. IC can be used for the monitoring of both analytes in natural and treated waters. For perchlorate, EPA Method 314.0 (Determination of perchlorate in drinking water by ion chromatography) has been developed, which suggests the use of a Dionex IonPac AS16 anion exchange column (or equivalent) with a 35 mM NaOH eluent and suppressed conductivity detection. Finally, there has also been much interest in recent years in the contamination of groundwater, well water, and drinking water supplies with hexavalent chromium. An EPA method has been developed utilizing IC for hexavalent chromium determinations (EPA Method 218.6). This method specifies the use of a high-capacity Dionex IonPac AS7 anion exchange column and UV/Vis detection following postcolumn reaction with diphenylcarbazine. Figure 2 shows an ion chromatogram of a spiked and unspiked drinking water sample obtained using a modified version of EPA Method 218.6. Table 1 lists some of the IC methods prescribed by the US EPA for the analysis of drinking water including several oxyhalide disinfection by-products (DBPs). Note how inductively coupled plasma mass spectrometry (ICP-MS) is also used for bromate detection in Method 321.8.
3.0 µS
0.002 (A) Chromate
AU
Chromate (B)
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12 16 Time (min)
9 20
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Figure 1 Chromatogram of 10 inorganic anions and oxyhalides in a water sample using suppressed ion chromatography. Peak identification: 1 ¼ fluoride, 2 ¼ chlorite, 3 ¼ bromate, 4 ¼ chloride, 5 ¼ nitrite, 6 ¼ bromide, 7 ¼ chlorate, 8 ¼ nitrate, 9 ¼ phosphate, 10 ¼ sulfate. (Reprinted with permission from Saari-Nordhaus R and Anderson JM Jr. (2002) Recent advances in ion chromatography suppressor improve anion separation and detection. Journal of Chromatography A 956: 15–22; & Elsevier.)
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Figure 2 Ion chromatograms of chromate in drinking waters: (A) unspiked sample, (B) sample spiked with 0.2 mg l 1 Cr(VI). (Reprinted with permission from Thomas DH, Rohrer JS, Jackson PE, Pak T, and Scott JN (2002) Determination of hexavalent chromium at the level of California public health goal by ion chromatography. Journal of Chromatography A 956: 255–259; & Elsevier.)
ION EXCHANGE / Ion Chromatography Applications 463 Table 1 EPA IC methods for drinking water analysis EPA method
Analysis
Method 300.1
Determination of inorganic anions and oxyhalides in drinking water by IC
Method 300.7
Determination of inorganic cations in drinking water by IC
Method 314.0
Determination of perchlorate in drinking water by IC
Method 317.0
Determination of inorganic oxyhalide disinfection by-products in drinking water using IC with the addition of a postcolumn reagent for trace bromate analysis
Rev. 2.0 Method 218.6
Determination of dissolved hexavalent chromium in drinking water, groundwater, and industrial wastewater effluents by IC
EPA Method 321.8
Determination of bromate in drinking waters by IC with ICP-MS detection
EPA Method 326.0
Determination of inorganic oxyhalide disinfection by-products in drinking water using IC incorporating the addition of a suppressor acidified postcolumn reagent for trace bromate analysis
Soil Analysis
Inorganic anions IC is used extensively for the determination of common inorganic anions in soil extracts. The key to valuable data when carrying out such analyses is the use of correct and reproducible extraction methods. For the determination of inorganic anions, often the soil is simply extracted using water. Such an application of IC is used to provide information on the fate of nutrient anions resulting from agricultural practices and to determine soil nutrient retention and leaching rates. Organic anions Both anion exchange chromatography and ion exclusion chromatography have been used extensively for the determination of low-molecular-weight organic acids in soil extracts. Malic acid, malonic acid, maleic acid, succinic acid, fumaric acid, ascorbic acid, citric acid, isocitric acid, succinic acid, tartaric acid, oxalic acid, and glycolic acid can all be determined using these techniques. Inorganic cations For the extraction of cations from soils, a number of approaches are used, dependent on whether the analyst wishes to determine labile or nonlabile cation concentrations. Extractions can be carried out using simply water or electrolyte solutions, or strong acid solutions for nonlabile cations. In this way, IC can also be used to determine the ion exchange capacity of the soils in question. Recently, IC has also found increased application in the field of metal speciation. Short anion exchange columns have been used for the rapid separation of anionic species of arsenic, selenium, and chromium,
extracted from contaminated soils, and followed by elemental specific detection. Atmospheric Samples
The determination of ambient concentrations of gaseous nitrogen- and sulfur-containing species (predominantly nitrate and sulfate) in the atmosphere has also been carried out using IC after collection using passive samplers. Wet denuder systems have also been developed for the collection of soluble ionogenic trace gases and soluble ionic species adsorbed onto atmospheric particles, used on-line with IC for continuous monitoring purposes. The use of large-volume filter-based samplers for the collection of atmospheric particulates has also been combined with IC for the determination of absorbed metal species. Collected samples are extracted from the filters and desorbed from the particulate matter using acidic solutions prior to analysis by IC combined with elemental selective detection such as ICP-MS. Hexavalent chromium, platinum, and palladium have been determined in this way, as have many other transition and heavy metal ions. Rainwater Automated rainwater collectors have been used in combination with IC for the determination of low-level concentrations of dissolved inorganic anions or cations. Due to the ‘clean’ nature of the sample, online preconcentration of the analytes can be readily achieved using short ion exchange preconcentrator cartridges onto which large sample volumes can be loaded, prior to elution onto the appropriate separator ion exchange column. This approach is used for the ultratrace analysis of rainwater samples.
464 ION EXCHANGE / Ion Chromatography Applications Table 2 Examples of foodstuffs to which IC has been applied for anion determinations following appropriate extraction methods Anions
Sample matrix
Nitrate, nitrite, sulfate, phosphate, chloride Fluoride Iodide Sulfite Bromide Chlorite and chlorate Bromate Iodate Chromate Selenite and selenate Arsenite and arsenate Cyanide
Milk products, fruits and fruit juices, beverages and alcoholic products, meat products, bakery products, vegetables, cereals As above plus citrus fruits and leaves and spinach Seafood, food colorings, and iodized table salt Beer, lemon juice, potatoes, seafood, fruits (grapes) Milk, food colorings, rice products, bakery products Vegetables Bakery products Iodized table salt Orange juice, potato products Vegetables, cereals, orange juice Food supplements, cereals, vegetables Fruits and fruit juices
An alternative approach has been developed based on a weakly acidic cation exchange column, used with a dilute tartaric acid/crown ether eluent, which resulted in the ability to separate both inorganic anions (chloride, nitrate, and sulfate) and inorganic cations (sodium, potassium, ammonium, calcium, and magnesium) simultaneously in real rainwater samples. The anions were retained through an ion exclusion mechanism and the cations were retained through a simple cation exchange mechanism. Sensitive detection was achieved using direct conductivity.
Industrial Applications Food and Beverages
As with most chromatographic methods applied to solid samples, sample digestion and analyte extraction methods are all important. IC is finding application in the analysis of foodstuffs following sample preparation using such techniques as microwave digestion, supercritical fluid extraction, accelerated solvent extraction, and pyrohydrolysis. Inorganic anions The predominant anionic species determined in foodstuffs are once again the nitrogen-, sulfur-, and phosphorus-containing species, as well as the halide ions. Table 2 lists some inorganic anions and some of the foodstuffs that have been analyzed for these anions using IC. Some of the more important applications in food analysis include nitrates and nitrites in baby food products, excess of which can lead to induce methemoglobinemia (blue baby syndrome), and the monitoring of sulfite, which is added to many foodstuffs as a preservative and to bleach food starches, and is only recently being linked to serious health effects. Also, residual bromate can be monitored in bakery products from the continuing use of bromate salts as dough conditioners.
Organic acids In beverages such as wines, beers, and fruit juices, IC has also been widely applied in the determination of various organic acids, although in many cases ion exclusion chromatography is often used in preference to anion exchange. Sugars In the brewing industry, IC is used for the determination and monitoring of fermentable sugars, such as glucose, fructose, isomaltose, sucrose, maltose, maltotriose, and numerous others. For sensitive detection, pulsed amperometric detection is often preferred. Inorganic and organic cations In the analysis of foodstuff extracts and digests, IC has been predominantly applied to the determination of alkali and alkaline earth metal ions and, to a lesser extent, selected organic amines. Alkali and alkaline earth metal ions are naturally present in most foodstuffs, although accurate monitoring is still necessary to evaluate nutritional values, e.g., the sodium or calcium content of foodstuffs. As mentioned previously, ammonium content can also be determined using IC simultaneously with alkali metal ions, and is often used as an indicator of food quality. Transition and heavy metal ions have also been determined in foodstuffs using IC, particularly seafood, where heavy metal contamination with metals such as cadmium and lead is often a problem. After separation using cation exchange or ion interaction chromatography, sensitive detection is generally achieved using postcolumn reaction detection with a suitable color-forming ligand, such as 4-(2-pyridylazo) resorcinol (PAR). Other metals such as zinc, copper, iron, cobalt, nickel, chromium, and manganese can also be detected in this way. In an interesting recent application, the determination of acrylamide in foodstuffs has been shown using accelerated solvent extraction followed by IC
ION EXCHANGE / Ion Chromatography Applications 465
with either UV or MS detection. Extracted samples can be analyzed directly using IC, with limits of determination of 50 ng per g acrylamide in foodstuffs possible using MS detection with single ion monitoring (SIM) at m/z 72. Pharmaceuticals
In the preparation of pharmaceutical products, the purity of reagents is of utmost importance. IC is often used for trace anion and cation determinations in starting materials, the simplest of which is reagent grade water. However, actual pharmaceutical preparations are often complex mixtures and IC provides alternative column selectivity to standard reversedphase HPLC, and is often more suited for the separation of very polar organics commonly used in pharmaceutical products. Table 3 lists some of the organic species that have been determined using IC. Often for such analytes UV absorbance is the preferred mode of detection, provided the analyte contains a suitable chromophore.
sodium, chloride, and sulfate on a near-real-time basis, and can also differentiate among different oxidation states of ions such as nitrate, nitrite, sulfate, and thiosulfate. These oxidation states respond to the general oxidizing tendency of coolant waters, which is an important variable in controlling localized corrosion. Some impressive recent applications of IC within this industry include: the determination of mono-, di-, and tributyl phosphates, the latter of which is an important compound used in the area of nuclear fuel reprocessing; the determination of long-lived artificial radionuclides resulting from fission reactions using IC coupled to ICP-MS detection; the use of IC to determine amines in amine-dosed feedwater used for erosion control in boiler tubes; and the application of IC to the determination of transition metal cations in the primary coolants of light water reactors. Figure 3 shows an ion chromatograph of a condensate discharge water sample from a fossil fuel power station containing trace amounts of inorganic anions and organic acids.
Nuclear and Fossil Fuel Power Generation Industry
As with the pharmaceutical products above, there is also great concern over contamination problems in the power generation industry. IC is extensively used to determine ultratrace concentrations of ionic species in process waters, coolant waters, wastewater, and other waste materials. The popularity of the technique is due to IC being one of a few analytical technologies that is able to measure ng per g concentrations of potentially corrosive ions such as
Semiconductor Industry
The semiconductor industry utilizes IC to monitor and identify the possible contamination of products during manufacture. Much of the application of IC is to trace inorganic anion analysis and, to a lesser extent, trace alkali and alkaline earth cation determinations. The sample matrices that are monitored using IC in the semiconductor industry include the large variety of chemicals used for cleaning,
Table 3 Examples of pharmaceutical preparations to which IC has been applied Analytes
Sample matrix
Column
Detection method
Citrate Saccharin aspartane, acesulfame-k, benzoate, sorbate, caffeine, theobromine, theophylline Trifluoroacetate Alenalol, metaprolol, alprenolol, oxprenolol, acebutolol, propanolol Paracetamol, salicylate Alkyl sulfonic acids Alendronate
Liquid and tablet formulations Tablet preparations
Anion exchange Anion exchange
Indirect UV absorbance Tunable UV absorbance
Cell-based products b-Blocker tablet preparations
Anion exchange Anion exchange
Suppressed conductivity Tunable UV absorbance
Tablet preparations Sulfonated sugar preparations Dosage formulations
Anion exchange Anion exchange Anion exchange
Injection formulations
Cation exchange
UV absorbance Suppressed conductivity Electrospray mass spectrometry Nonsuppressed conductivity
Antibiotic preparations Hypocholesterolemic agent preparations
Cation exchange Cation exchange
UV absorbance Nonsuppressed conductivity
Catecholamines (norepinephrine, epinephrine, dopamine) Tetracyclines Amylamine, t-butylamine
466 ION EXCHANGE / Ion Chromatography Applications
help in the diagnosis of lactic acidosis in diabetic patients.
0.75 6
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20 Retention time (min)
30
Figure 3 Ion chromatogram of a condensate discharge water sample. Peak identification: 1 ¼ fluoride, 2 ¼ acetate, 3 ¼ formate, 4 ¼ chloride, 5 ¼ nitrite, 6 ¼ carbonate, 7 ¼ sulfate, 8 ¼ unknown, 9 ¼ nitrate, 10 ¼ unknown, 11 ¼ phosphate. (Reprinted with permission from Lu Z, Liu Y, Barreto V, et al. (2002) Determination of anions at trace levels in power plant water samples by ion chromatography with electrolytic eluent generation and suppression. Journal of Chromatography A 956: 129–138; & Elsevier.)
washing, polishing, and treating surfaces, such as reagent water, solvents, strong acids and bases, and oxidizing agents. Process gases and clean room gases, and filtered air are also monitored.
Biological Applications Analysis of Blood, Plasma, and Serum
The ability to determine quantitatively certain ionic analytes in blood, plasma, and serum samples can be of substantial benefit to those attempting the diagnosis of certain diseases, particularly where concentrations of these analytes are known to be directly related to specific physiological disorders. Anions IC has established itself as the method of choice for the determination of common anions such as chloride, sulfate, and phosphate in blood and serum samples. For example, a common clinical application of IC is the study of sulfa drug metabolism through the monitoring of blood sulfate levels. Samples are generally pretreated using ultrafiltration or acidification and centrifugation, or both. Both IC and ion exclusion chromatography have been applied to the determination of bicarbonate in blood plasma. Ion exclusion has also been extensively applied to the determination of certain organic acids in blood plasma, such as pyruvate and lactate, the latter of which is used to
Cations There have been many applications of IC to the determination of sodium, potassium, and ammonium in blood serum. In most cases, serum samples were simply ultrafiltered and injected directly. In other cases only dilution was necessary. Total and free concentrations of calcium and magnesium in blood serum can also be determined using IC. Total concentrations can be determined using sample acidification followed by centrifugation. Free concentrations of the cations can be determined after passage of the untreated sample through a cation exchange solid-phase extraction (SPE) cartridge to trap the cations and isolate them from those ions bound to serum proteins. Analysis of Urine
As with blood, urine analysis is used in clinical studies, and the relative concentrations of various ionic species are of great importance in both disease diagnostic and drug metabolism studies. For example, IC is used to determine urine oxalate concentrations. Urinary oxalate levels are an important parameter in urolithiasis research (kidney stones). Other anions that can be determined in urine using IC include phosphate, sulfate, bromide, citrate, nitrate, nitrite, and thiosulfate. As with blood and serum samples, both ultrafiltration and centrifugation are often used as sample cleanup steps. Interesting applications include the use of IC coupled with ICP-MS detection for the determination of anionic arsenic species in urine resulting from occupational and dietary exposure. Species include urinary arsenate, arsenite, dimethylarsinic acid, and methylarsonic acid, and are separated using a hydrophilic anion exchange resin with a weak acid eluent. Studies have also been carried out using IC and ion interaction liquid chromatography to determine human urinary thiocyanate concentrations and relate concentrations found to levels of smoking. Thiocyanate is the main metabolic product of cyanide inhaled with cigarette smoke. Figure 4 shows overlaid ion chromatograms of a smoker’s urine sample and the same sample spiked with thiocyanate. The chromatograms shown were obtained using ion interaction chromatography, utilizing a short reversedphase column and a tetrabutylammonium chloride and methanol eluent. Detection was carried out using direct UV absorbance at 230 nm. Analysis of Saliva and Sweat
Finally, IC methods have been applied to the determination of both inorganic anions and alkali and
Response (AU)
ION EXCHANGE / Chelation Ion Chromatography 0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0
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See also: Ion Exchange: Overview; Principles; Ion Chromatography Instrumentation; Chelation Ion Chromatography; Isolation of Biopolymers; Isotope Separation. Thiocyanate
Further Reading
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Time (min) Figure 4 Analysis of urine for thiocyanate using ion interaction liquid chromatography. Lower trace: sample (heavy smoker) diluted 1:20. Upper trace (heavy smoker) diluted 1:20 and spiked with thiocyanate.
alkaline earth cations in saliva. The sample matrix is relatively simple compared to other biological fluids and can be analyzed directly or simply diluted prior to injection. IC methods have also been developed for the determination of sweat samples for ionic analytes. Methods looking at sulfate levels and also concentrations of sodium and potassium in sweat samples have been developed, with relative levels of the latter metal ions being useful indicators of several important diseases, one of which is cystic fibrosis.
Betti M (1997) Use of ion chromatography for the determination of fission products and actinides in nuclear applications. Journal of Chromatography A 789: 369–379. Buldini PL, Cavalli S, and Trifiro A (1997) State-ofthe-art ion chromatographic determination of inorganic ions in food. Journal of Chromatography A 789: 529–548. Haddad PR and Jackson PE (1990) Ion Chromatography. Principles and Applications. Amsterdam: Elsevier. Lopez-Ruiz B (2000) Advances in the determination of inorganic anions by ion chromatography. Journal of Chromatography A 881: 607–627. Singh RP, Smesko SA, and Abbas NM (1997) Ion chromatographic characterisation of toxic solutions: analysis and ion chemistry of biological liquids. Journal of Chromatography A 774: 21–35. Small H (1990) Ion Chromatography. New York: Plenum. Smith RE (1987) Ion Chromatography Applications. Boca Raton, FL: CRC Press. Vanatta LE (2001) Application of ion chromatography in the semiconductor industry. Trends in Analytical Chemistry 20: 336–345.
Chelation Ion Chromatography P Jones, University of Plymouth, Devon, UK P N Nesterenko, Lomonosov Moscow State University, Moscow, Russia & 2005, Elsevier Ltd. All Rights Reserved.
Introduction It is now over 60 years since the development of column ion-exchange chromatography using polymeric resins. Interestingly, little has changed since then in terms of the basic separation processes for inorganic anions and cations. The renaissance in the 1970s, where ion-exchange was the principal process in a group of techniques now known as ion chromatography (IC), was mainly associated with the improvement in efficiency of stationary phases and detection systems rather than new types of ionexchange groups or elution systems. In essence, the IC separation of metal ions principally involves the use of eluents containing complexing organic acids,
such as tartaric, citric, oxalic, combined with high efficiency stationary phases. The complexing strength of acid and concentration chosen depended on whether the ion-exchange substrate was cationic, anionic, or mixed. Although poly(styrene–divinylbenzene) (PS–DVB) based resins are still the most common substrate, silica-based materials are increasingly being used. There are a number of problems associated with present IC methods involving high efficiency ion-exchange separations of metal ions, the two principal ones being sensitivity to ionic strength and limited selectivity. The influence of ionic strength is particularly serious as a relatively large salt concentration in the sample can drastically affect the chromatography, in many cases making it impossible to resolve the analytes. Limited selectivity is also a restriction, as once the substrate is chosen for conventional ion-exchange separations there are only a small number of cases where changes in eluent composition can significantly alter separation order.