- Email: [email protected]
Current instrumentation for aerosol mass spectrometry
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Current instrumentation for aerosol mass spectrometry Kari Hartonen, Totti Laitinen, Marja-Liisa Riekkola This review describes recently presented instrumental set-ups for aerosol mass spectrometry (AMS), most being suitable for in-situ analysis. AMS allows the analysis of atmospheric aerosol particles within a short time interval and without sample pretreatment, and it is less sensitive to artifact formation than conventional sampling and analytical techniques. Although a quantitative measure of total organic loading can be obtained with some AMS instruments, they currently give only limited information on specific compounds. When the ionization technique produces a large number of fragments for a compound, it becomes impossible to track the original compound. Moreover, at present, there is no commercially available instrument capable of quantitative analysis of chemical compounds in ambient aerosol particles with diameters of 0.003–50 lm and simultaneously offering short time resolution. We pay special attention to the technical and methodological challenges of AMS, whose benefits we demonstrate with selected applications. ª 2011 Elsevier Ltd. All rights reserved. Keywords: Aerosol mass spectrometry; Aerosol particle; Desorption; Detection; Fragment; In-situ analysis; Instrumentation; Ionization; Mass analyzer; Particle size
1. Introduction Kari Hartonen*, Totti Laitinen, Marja-Liisa Riekkola University of Helsinki, Department of Chemistry, Laboratory of Analytical Chemistry, P.O. Box 55, FI-00014, Finland
*
Corresponding author. Tel.: +358 919 150 265; Fax: +358 919 150 253; E-mail: [email protected], [email protected], [email protected]
1486
Mass spectrometry (MS) is well suited for the direct analysis of gas and particle phases in air, thanks to the fast response, excellent sensitivity, and qualitative (structural) information provided. Moreover, MS can be regarded as a universal detector with the potential for highly selective mode of operation. Direct monitoring and analysis of gas-phase compounds is relatively straightforward, since samples are easily introduced through a membrane inlet or as a small gas flow into the ionization chamber of the MS [1,2]. Aerosols (suspended solid or liquid particles in gas phase) are of major interest today because of their impact on human health and their tendency to cool the EarthÕs climate (although aerosols, containing, for example, black carbon, can have the opposite effect). The effect that aerosols have greatly depends on their size, chemical composition, and concentration. Some aerosols, for example, contain dangerous species (e.g., microbiological, biological, and chemical toxins), which are a threat to human health. In particular, very fine particles are able to penetrate deep into the respiratory system. Size segregation (or particle-size informa-
tion) is usually essential in MS investigations of atmospheric aerosols. Not only does the relative portion of organic matter tend to increase with decreasing size of the particles, but our understanding of aerosol formation and growth processes, so critical in climate studies, depends upon resolving the chemical composition of ultra-fine nucleation particles [3]. Conventionally, aerosol particles have been collected onto filters and extracted with organic solvent to release compounds for analysis. This approach has several drawbacks (e.g., the long collection time may lead to alteration of the compounds through oxidation, gas-phase compounds may be absorbed or adsorbed, and volatiles may be lost). Moreover, the study of short-lived processes is not possible because of poor time resolution of the data (long collection time needed to obtain sufficient amount of analytes for detection). Although sensitive on-line MS analysis allows real-time or near-real-time measurement, it is essential in MS analysis of aerosols that compounds are first vaporized or desorbed from particles into gas phase and then ionized. Usually, the particles are size separated before these two steps, so that information on chemical
0165-9936/$ - see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2011.06.007
Instrument AMS with two-step laser desorption and ionization Laser-ablation AMS (ALABAMA)
Sample
Desorption
Single particle
TEA-CO2 laser
Single particle
UV laser, 266 nm (ablation + ionization), 2.5 · 108 W/cm2, 2.6 · 109 W/cm2* Solvent desorption (extraction)
Ionization Tunable VUV laser, 122– 168 nm UV laser, 266 nm (ablation + ionization), 2.5 · 108 W/cm2, 2.6 · 109 W/cm2* Electrospray ionization (ESI)
Mass analyzer
Particle size
Ion trap (IT)
P 300 nm
Caffeine aerosol particles, gas-phase compounds
Bipolar-TOF
150–900 nm
Measurement of organic and inorganic compounds during MEGAPOLI 2009 campaign (Paris)
FT-ICR, QTOF API-US
6500 nm
Secondary organic aerosols (SOA) from the ozonolysis of monoterpenes in flowtube reactor Primary, secondary, ambient organic aerosols. Ambient aerosol SOAR-1 study in Riverside, CA, USA; MIRAGE C-130 aircraft study near Mexico City. Atomic ratios O/C, H/ C, N/C, and OM/OC Quantitative analysis of ambient organic compounds
http://www.elsevier.com/locate/trac
High-resolution FTICR-MS, nanoaerosol MS (NAMS)
Particle collection (2– 120 h)
High-resolution TOF-AMS
Single particle
Thermal vaporization at ca. 600C
Electron impact (EI)
TOF
35 nm–1.5 lm
High-mass resolution thermal desorption (TD) PTR-MS
Particle collection
Thermal desorption up to 350C
Chemical ionization (CI)
TOF
Humidified atmospheric particles <2.5 lm
Laser desorption/ ionization TOF-MS
Single particle
UV laser 266 nm*
UV laser 266 nm*
TOF
250 nm–2 lm
Two-step laser desorption-ionization AMS
Particle collection (electrostatic deposition)
IR laser 1064 nm
UV laser 193 nm
TOF
19, 30 and 22 nm, 10– 50 nm
Laser desorption (LD) Particle and laser ionization (LI) collection TOF-MS
Vis laser 532 nm (ca.5 MW/cm2)
UV laser 266 nm (1–2 MW/cm2)
TOF
Gases and particles of all sizes
Laser desorption/ ionization (LISPA)AMS
UV laser 248 nm (107 W/cm2)*
UV laser 248 nm (107 W/cm2)*
TOF
250 nm–1.3 lm
Single particle
Application
Comments
Ref.
No sample preparation, good [4] sensitivity, and selective ionization Small, handy instrument, [5] aircraft measurements
High mass resolution and good identification, comparison with LC-MS
[6]
High resolution for rapid [7,8] single particle analysis in real-time (detection limits for sub-lm aerosol <0.04 lg/m3 in the high-sensitivity mode and <0.4 lg/m3 in the highresolution mode)
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Table 1. Aerosol mass spectrometry (AMS) instrumentation used in aerosol research
High-resolution TOF-MS. [9] Transfer line from TD unit to PTR-MS at 180C. Comparison with OC from filter sampling Polystyrene latex particles [10] and metallic solution used to perform size and mass calibration
1487
Trends
Ambient aerosols in Guangzhou City, China, classification of aerosols into different groups by their chemical composition Self-generated particles, Sample collection at [11,12] ambient particles, black atmospheric pressure, rapid carbon, and liquid samples sample introduction to MS vacuum via special sampling valve Chemical composition Flame studies of soot [13] (PAHs) of soot particles formation process with filter sampled from a lowcollection. Soft ionization in pressure flame MS Characterization of aerosol Good correlation with [14] particles in Tokyo, Japan Aerodyne AMS; ammonium, sulfate and organic compounds detected (continued on next page)
Trends
1488 Table 1. (continued) http://www.elsevier.com/locate/trac
Instrument
Sample
Desorption
Ionization
Mass analyzer
Particle size
Application
Comments
Ref.
Design of metastable atombombardment ionization for AMS, MAB compared with EI and VUV Nanoparticle detection and identification at elemental level; test nanoparticles produced from several pure chemicals
Sensitive ionization with less fragmentation, real-time alternation between MAB and EI Atomic composition from studied compounds, particles trapped inside ion trap for laser ablation followed by TOF-MS analysis Very sensitive instrument suitable for near-real-time study of particle formation and growth, LOD 89 fg for pinic acid and 8.8 pg for cholesterol Soft ionization method, suited for the analysis of particle-phase and gas-phase organics
[15]
Single particle
Thermal desorption
Metastable atom bombardment (MAB), EI
TOF
P 35 nm
Particle collection inside ion trap (IT)
Ablation with Vis laser 532 nm (160 mJ)*
Ablation with Vis laser 532 nm (160 mJ)*
TOF
<30 nm
Near-infrared (NIR) laser desorption/ ionization (LDI) AMS
Particle collection
NIR laser 1064 nm (80 MW/cm2)*
NIR laser 1064 nm (80 MW/cm2)*
TOF
180 nm on average
Detection of primary and secondary organics in chamber studies
Photoelectron resonance capture ionization (PERCI)AMS
Particle collection
Thermal vaporization probe (up to 400C)
TOF
50–380 nm
Photoionization AMS (PIAMS)
Particle collection
IR laser, 1064 nm
UV laser, 235– 300 nm (100 mJ/ cm2) focused to aluminum photoelectrode UV laser, 118 nm
TOF
<300 nm
Quantitative analysis of organics from aerosols pneumatically generated from dilute standard solutions Organics on fine and ultrafine particles
Proton-transferreaction MS (PTR-MS)
Single particle
Thermal vaporization at 120/150C
Chemical ionization (CI)
Quadrupole
0.52 20 lm
AMS with VUV radiation generated by resonance difference frequency mixing (RDFM)
Single particle
IR laser or impaction on heater
VUV laser, 142 nm (with RDFM) or 118 nm
TOF
Micrometer range
Laser desorption/ ionization AMS (SPAMS)
Single particle
UV laser, 266 nm (2.4 or 2.7 nJ/ lm2)*
UV laser, 266 nm (2.4 or 2.7 nJ/ lm2)*
Bipolar-TOF
Micrometer range
Drug identification from multi-component tablets
ITMS with laser desorption and EI ionization (SPIT-MS)
Single particle
IR laser, 10.6 lm (50 mJ/5 · 107 W/ cm2)
Electron impact (EI)
Ion trap (IT)
0.1–1.1 lm
Laboratory-generated pure aerosols (caffeine, oleic acid, linoleic acid, dihydroxybenzoic acid)
Chamber measurements for secondary organic aerosol (SOA), pinonic acid particles Detection of oleic acid with minimal fragmentation
Selective desorption on the collection probe, soft ionization Gas-phase analysis. Also suitable for on-line secondary organic aerosol (SOA) analysis RDFM producing less fragmentation and more intensive molecular ion for oleic acid. More homogeneous heating with heater than with IR (CO2) laser. Excellent S/N ratio Fast, non-destructive method for drug screening from multi-component samples, no need for sample pretreatment MS2 possibility and EI ionization. Vaporization and ionization inside the ion trap, high sensitivity
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Thermal desorptionmetastable atom bombardment ionization (MAB)-AMS Nanoaerosol mass spectrometer (NAMS)
[25] Introduction of fragile biomolecules to gas phase as nanoparticles and their fragment-free photoionization 70–1000 nm
One laser used for both desorption and ionization.
2. Instrumental solutions for aerosol mass spectrometry
*
TOF Single particle Vacuum-UV-AMS
Thermal vaporization (298–873 K)
UV laser (tunable, 7–25 eV)
3 nm–2 lm Triple quadrupole Chemical ionization (CI) Thermal desorption (up to 500C) Particle collection Thermal desorption and chemical ionization MS (TDCIMS)
Trends
composition can be obtained as a function of particle size. Aerosol MS (AMS) techniques can usefully be divided into two groups: those analyzing single particles, and those analyzing many particles of a certain size collected over a short period of time. Whatever the sampling system, direct MS analysis will always produce mixed spectra of the many components present in the aerosols (aerosols of pure compounds are excluded). Chemometric tools for data analysis and use of tandem MS (MS2) techniques are an invaluable assistance for resolving the complex spectral information. High mass resolution can facilitate the analysis by providing possible molecular formulas for the ions, and softer ionization techniques will provide less fragmentation and less complex spectra for interpretation (or molecular ions suitable for MS2 characterization). Particles collected off-line on surfaces (e.g., filters or impactor plates) can be analyzed by MS using desorption techniques {e.g., SIMS [26]} and novel ambient desorption/ionization techniques {e.g., DAPPI [27] or DESI [28]}. Although, in the strict sense, these are not AMS techniques, with a short enough collection period, they could perhaps be applied in on-line, near-real-time aerosol analysis, and they might be used for the detection of compounds present in high abundance. They could also be applied as alternatives to the laser or thermal desorption generally used in AMS. On-line aerosol-particle analysis has already been successfully performed with matrix-assisted laser desorption ionization (MALDI), where an aerodynamic lens system is applied to focus the aerosol beam onto a MALDI target plate [29]. We describe below various AMS systems and approaches enabling in-situ analysis of atmospheric aerosols within a short time interval and without sample pretreatment. We cover selected applications in the final section.
Detection of aminium salts in atmospheric nanoparticles. Measurements in Mexico City and in the boreal forest at Hyytia¨la¨, Finland Biological nanoparticles (from amino acids and polypeptides)
Aminium-salt formation found to be widespread and could account for a significant part of nanoparticle growth
[24]
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Many different AMS set-ups are possible, varying with the type of aerosol inlet, aerosol sizing, desorption, ionization, and MS-analyzer system employed. There are two commercial AMS systems (TSI and Aerodyne) but the first is no longer available on the market. The TSI system comprises a nozzle-skimmer system for aerosol inlet, lasers for particle-velocity measurement and sizing, and a laser for desorption/ ionization before the bipolar time-of-flight (TOF) MS measurement. The system is based on the ATOFMS design of Gard et al. [30]. The second (Aerodyne) utilizes an aerodynamic lens system for particle-beam focusing, a chopper to pulse the beam onto the thermal desorption surface, followed by electron-impact (EI) ionization before MS analysis [7]. In this system, particle size is http://www.elsevier.com/locate/trac
1489
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
deduced from the flight time of the particle between the chopper and the detector (a sizing system with light scattering of laser radiation has been demonstrated [31]). Several commercial models of the second system exist, with different MS analyzers incorporated (quadrupole and TOF with different resolution). Besides commercial instruments, many self-made AMS constructions and set-ups have been described, and these are the focus of this review. Table 1 summarizes selected technical solutions and variations for AMS instrumentation. 2.1. Aerosol sampling and size separation In AMS systems, air particles are typically sampled through a small orifice, usually ca. 100 lm, resulting in 80–90 mL/min flow into vacuum (1.6–3 Torr) [16,19,23]. In some studies, orifices of 80 lm [10] and even 260 lm [32] have been employed. In the latter case, the air flow into the vacuum system was as high as 500 mL/min. The flow-limiting critical orifice leading into the vacuum system allows the aerosol flow to be focused by an aerodynamic lens system. In general, the aerodynamic lens system is used to focus aerosols from ca. 0.040–1 lm into a very tight beam, though transmission efficiency is close to 100% only for particles in the 60–600-nm range. Efficiency drops off noticeably for smaller and larger particles (e.g., 25% efficiency for 1 lm) [5]. Fortunately, however, the lens system can be designed and optimized for nanoparticle transmission, as has been successfully done for 3–30 nm particles [33]. The aerodynamic lens system is definitely the most popular choice for particle-beam focusing (into a point where particle collection or desorption/ionization of a single particle will occur). From the aerodynamic lens system, the particles pass through a nozzle that controls the supersonic gas expansion into high vacuum. Particle velocities are in the range of 50–400 m/s [23]. Velocity (and size) is generally determined by the detection of scattered light by two laser–photomultiplier tube (PMT) pairs located at a fixed distance from each other. Laser of wavelength 532 nm is the most common for particle detection and sizing {typically on the order of 100 mW/ cm2 [23]}. As many as six laser–PMT pairs have been used to track the particles after air flow through a converging nozzle into differentially pumped vacuum and particle focusing [22]. As a replacement for lasers, Benner et al. [34] developed a single-particle image-charge detector for their AMS to measure the velocity and thereby the size of particles. Both particle size and velocity need to be known in order to hit a single particle with a desorption/ ionization laser. However, since particles smaller than ca. 100 nm do not scatter light, desorption/ionization of a single particle in this size range becomes a question of luck. There are only a few AMS systems that do not make use of the aerodynamic lens. One system exploited var1490
http://www.elsevier.com/locate/trac
ious pre-cut-offs in front of the inlet (for different size fractions) [9], and the increase in the aerosol-collection flow from 0.9 L/min to 9 L/min was found to improve the sensitivity 10-fold. In another approach, particles were charged, after which a differential mobility analyzer (DMA) was utilized for the size separation [11]. In this latter set-up, the charged and size-separated particles were collected via electrostatic deposition on a surface of the sampling valve working as an interface between the atmospheric collection and high MS vacuum. 2.2. Desorption and ionization Compounds in aerosol particles are most frequently desorbed through a quick temperature increase (vaporization). Single particles are directed toward a hot surface and flash vaporized in the vicinity of the surface. Alternatively, particles can be collected onto the surface for a short time and then desorbed through resistive heating of the surface (fast thermal desorption). Heating and desorption can also be achieved by a short pulse from an IR laser. For single-particle analysis, the laser beam needs to be well timed, aligned, and focused in order to hit the arriving particle. Timing is less critical for those AMS systems that utilize collection on a surface close in size to that of the laser beam (a few mm in diameter), but still the laser beam needs to be positioned well. Fig. 1 shows an example of thermal desorption with a vaporization probe where the coiled Nichrome filament can be resistively heated up to 400C to vaporize the particles. Alternatively, the probe can be operated at constant temperature (400C) to flash vaporize the incoming single particles. Desorbed compounds are ionized by a laser generating photoelectrons from an aluminum photocathode [18]. Interestingly, one of the commercial AMS instruments (Aerodyne) has also been modified by the addition of metastable-atom bombardment (MAB) ionization (Fig. 2). After flash vaporization near the hot surface (typically 600C), the vapor plume is ionized by either EI or MAB. In MAB, argon, krypton or nitrogen was employed as discharge gas [15]. Less fragmentation of organic compounds was produced by MAB than by EI, at least at the lower vaporization temperature of 180C. Also, a vacuum-UV lamp with 2 mm i.d. and MgF2 window has been successfully connected to one side of the AMS vaporization and ionization region just 9 mm from the center of the heated vaporization surface. Less fragmentation is achieved through sensitive photoionization, as was clearly demonstrated for pristine [35]. Lasers are frequently applied for desorption and ionization due to the high sensitivity that they can provide, and the resulting soft photoionization with less fragmentation. The energetic lasers with pulses of a few ns that are typically used also fit well with TOF analyzers.
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Trends
Figure 1. (a) Photoelectron resonance capture ionization aerosol mass spectrometry (PERCI-AMS), which comprises five main components: (1) particle inlet; (2) particle collector/vaporization probe (VP); (3) aluminum photoelectrode (PE); (4) tunable UV pulsed laser; and, (5) time-of-flight mass spectrometer along with necessary electronics and data-processing equipment. (b) Close-up of ion-extraction region that includes photoelectrode, vaporization probe, and ion-extraction electrode (Reprinted with permission from [18]).
Figure 2. The metastable atom beam source coupled to the aerosol mass spectrometry (AMS) ionization region (Reprinted with permission from [15]).
Laser–particle interactions have been studied in some detail by Zhou et al. [36]. Selectivity of the lasers (especially in ionization) can be a benefit or a drawback. An IR laser is generally employed, at either 1064 nm or 10.6 lm wavelength, for desorption, while UV at 266 nm or vacuum-UV at 118 nm is the preferred laser for the ionization of molecules. Lasers are also used along with other desorption and ionization techniques. Use of two lasers requires that the timing (delay) between the lasers be carefully optimized. Fig. 3 shows a typical setup for AMS with two-step laser desorption (IR) and ionization (VUV) of a single particle. If a single laser pulse is used for desorption and ionization, typically the UV laser is utilized. With UV (266 nm) ablation at 2.5 · 108 W/cm2, the maximum ablation efficiency was 96% for 400-nm polystyrene
latex particles and >90% for the entire size range 240– 500 nm [5]. However, a more intense beam (2.6 · 109 W/cm2) was necessary for the ionization of NaCl particles. Zelenyuk et al. [37] have made a detailed comparison of UV ablation and IR-UV two-step laser desorption and ionization. Recently, a 532-nm laser was applied for desorption in soot analysis but the intensity was much higher than that used for detection and sizing of particles [13]. Fig. 4 illustrates an AMS system where a CO2 laser is used for particle desorption. The CO2 desorption laser enters at 35.2o angle between the ring and end cap to intersect with the particle beam (coming through a 2-mm hole in the ring electrode) in the center of the trap. For desorption, a 250-mm ZnSe lens focuses the output
http://www.elsevier.com/locate/trac
1491
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Figure 3. Single aerosol-particle laser time-of-flight (TOF) instrument. Particles are focused in the aerodynamic lens, detected and sized in the two light-scattering regions, then vaporized and ionized in the extraction region of the TOF mass spectrometer (TOF-MS) (Reprinted with permission from [21]).
Figure 4. Instrument set-up for ion trap mass spectrometry (IT-MS) using laser desorption and electron impact (EI) (Reprinted with permission from [23]).
of the CO2 laser to a spot ca. 1 mm in diameter inside the ion trap [23]. AMS-like systems with the particle collection outside the MS vacuum have been described. In one of these, the aerosol sample collected is kept in a preparation chamber at 160C before introduction to the MS through a gate valve [13]. In another system, before two-step laser desorption and ionization, the sample probe is inserted into the ion trap through the vacuum interlock without
1492
http://www.elsevier.com/locate/trac
breaking the vacuum [38]. Both these approaches employ the old direct-insertion probe (DIP) concept, as does a solution that collects aerosol particles on a filter and makes use of thermal desorption and EI before MS analysis [39]. 2.3. Mass-spectrometry analysis Direct analysis of compounds in aerosol particles by MS always results in a mixed spectrum (except for aerosols
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Trends
Figure 5. High-resolution time-of-flight aerosol mass spectrometry (TOF-AMS) with reflectors (Reprinted with permission from [8]).
generated from pure compounds), and interpretation of the spectrum is challenging. The amount of reliable chemical information obtained (e.g., from air particles) is minimal. Several different techniques have been enlisted in the attempt to overcome this problem, namely: (1) softer and more selective ionization (discussed above); (2) high mass resolution; (3) MS2; and, (4) separation of compounds before MS. Fig. 5 depicts an AMS instrument with one (V mode) or three (W mode) reflections applied for the ion beam in a TOF analyzer. With m/z of 200, the mass resolution obtained was 2100 for V mode and 4300 for W mode [8]. Similarly, higher mass resolution (3500– 5000) has been used with proton transfer reaction (PTR)–TOF-MS in an attempt to squeeze more information from the spectral data (to access the molecular formulas of the ions) [9]. Nevertheless, the resolution obtained in these two studies was not of the quality (<5 ppm accuracy) generally required for molecular formula assignment. With use of FTICR-MS, Gao et al. [6] achieved excellent mass resolution for compounds in secondary organic aerosols (SOA), and reliable identification of compounds was also obtained by MS2 analysis. The ion trap (IT) is a good choice for the AMS analyzer, since it allows MS2 analysis. However, there are some drawbacks that limit its efficiency: (1) the total number of ions that can be stored simultaneously is limited by space charge; and, (2) the trapping efficiency for externally introduced ions is sometimes low. These two limitations were minimized in a set-up where separate lasers were employed for particle desorption and ionization in the center of the IT [38]. An aerodynamic lens system has been introduced with
minimal modification into the heated ion source of a commercial IT [49]. In addition, an IT has been employed for efficient trapping of 7–25 nm particles before TOF-MS analysis [16]. A separation step before MS has been incorporated in an aerosol-collection module and transfer line to gas chromatography–MS (GC-MS) for efficient characterization of SOA formed from b-pinene oxidation [50]. Preliminary measurements of ambient atmospheric aerosols were undertaken and the results presented. A technique closely related to AMS is atmospheric pressure interface (APi)-TOF-MS, which is used for the analysis of atmospheric ions and their clusters in realtime [51,52]. The instrument has been used for the detection of organosulfate, organic acids, inorganic acids (e.g., sulfuric acid) and their clusters, (poly)alkyl pyridines and (poly)alkyl amines. Although the instrument does not have an ionization source and detects only atmospheric ions, it can evidently be easily modified for the analysis of small particles. 3. Applications AMS is well suited for the on-line analysis of particulate matter in real time. It is deployable for field measurements in environmental studies and applicable for occupational health and safety investigations. Selected applications and the associated major findings are presented in Table 2. Many AMS applications have been designed for the investigation of different sizes of aerosol particles generated from pure compounds [11,16–18,21,23]. Typically, the studies on pure compounds involve the testing of instrumental performance, optimization of the instrumental conditions, and method development. Nevertheless, most AMS applications are aimed at the real task of resolving the chemical composition of
http://www.elsevier.com/locate/trac
1493
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Table 2. Selected different applications of aerosol mass spectrometry (AMS) and the results obtained Particle type, analytes Amines (trimethylamine) in fine particulate matter
Individual airborne, micron-sized, Mycobacterium tuberculosis H37Ra particles
Single micrometer-sized particles containing poly(ethylene glycol) (PEG)
Indoor airborne particles, tobacco smoke, insect repellents N,N-diethyl-3-methylbenzamide, bioallethrin, and piperonyl butoxide Silicon-carbide nanoparticles formed by thermal decomposition of tetramethylsilane
Actual or surrogate chemical, biological, radiological, nuclear, and explosive materials and illicit-drug precursors in aerosols Secondary organic aerosols from ozonolysis of apinene Aerosol particles in the Tokyo metropolitan area during summer 2008
Organic aerosols in Austrian Alps. Total of 638 mass peaks (18–392 Da) detected and quantified
Individual airborne cells in bioaerosols
Aerosol particles from diesel-car exhaust and wood combustion
Chemical warfare (CW)-related species in complex aerosol particles
Results
Ref.
Amines in fine particles were detected and quantified during ambient studies of winter inversions. Reaction rate of trimethylamine and nitrate radical was estimated at 4.4 · 10 16 cm3/molecules/s with a conversion rate to the aerosol phase of ca. 65%. Amines can contribute to SOA formation in areas where nitrate radical is a significant player in oxidation chemistry Using a distinct biomarker, the mass spectral signatures for aerosolized M. tuberculosis H37Ra particles were found to be distinct from those of particles of M. smegmatis, Bacillus atrophaeus, and B. cereus. For the first time, a potentially unique biomarker was measured in M. tuberculosis H37Ra at the single-cell level Optimization of bioaerosol mass spectrometer for complex biological samples, including human effluents. PEGs of average molecular mass >500 Da were detected in particles. Tripeptide tyrosine-tyrosine-tyrosine or 2,5dihydroxybenzoic acid was added as matrix to nebulized solutions to assist LDI with 266 nm or 355 nm laser, respectively Specific outdoor particles (e.g., dust and carbon particles) were detected in indoor air. Three main categories describing particles originating outdoors, in environmental tobacco smoke and in pesticides used indoor, were clearly distinguished With increasing temperature, particles formed and grew by coagulation. At higher temperatures, sintering of the particles became an important process. A simple model was used to compare the particle velocity in a molecular beam of AMS as a function of particle mass. The significant difference in the particle velocity could be explained by a change in the particle-shape factor due to sintering Laboratory experiment involving actual threat and surrogate releases mixed with ambient background aerosols showed broad-spectrum detection ability within seconds. Data from a field test at the San Francisco International Airport demonstrated extended field operation with an ultra-low false-alarm rate The limit of detection measured for pure oleic-acid particles (geometric mean diameter and standard deviation of 180 nm and 1.3 nm, respectively) was 140 fg (or 1.7 ng/m3/min sampling time) Spectra illustrated that approximately 95% of the oxygen-containing organic particles contained nitrate. Equivalent mass concentration of organic aerosol, traced by mass-to-charge ratio (m/z) 44, showed a close correlation with particulate nitrate and gas-phase odd oxygen, [O3+NO2], whereas equivalent mass concentration of organic aerosol, traced by m/z 57, did not Oxygenated hydrocarbons constituted the bulk of the aerosol mass (75%) followed by organic nitrogen compounds (9%), inorganic compounds (mostly NH3, 8%), unidentified/halogenated compounds (3.8%), hydrocarbons (2.7%), and organic sulfur compounds (0.8%) The mass spectral signature of individual Bacillus spores was characterized and the ability to distinguish two Bacillus spore species, B. thuringiensis and B. atrophaeus, was demonstrated It was demonstrated that the chemical profiles from different combustion sources (soft and hard wood combustion, gasoline and diesel car exhaust) can be well discriminated. Absolute detection limits in the zeptomole region were achieved for selected PAHs Observed semi-volatile species may have been chemisorbed on some particle surfaces in sub-monolayer concentrations and may remain hours after deposition. Identification of trace CW-agent-related species is feasible with this technique
[40]
atmospheric aerosols and investigating compound concentrations and the formation, growth, and fate of aerosols [5,7–10,12,14,24,40]. Often the results have been confirmed in reaction-chamber experiments [6,17,20], where similar reactions to those occurring in the atmosphere are simulated.
1494
http://www.elsevier.com/locate/trac
[41]
[42]
[43]
[44]
[45]
[46]
[14]
[9]
[47]
[48]
[49]
The typical compounds studied in atmospheric aerosols are ones arising from burning processes (e.g., PAHs) [13,48] and from reactions of biogenic compounds in the atmosphere (e.g., oxygenated terpene compounds) [9,46]. Usually some inorganic or total organic content is reported, or specific compounds that are easily
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Trends
Figure 6. Sammon mapping correlation tree for laser aerosol mass spectrometry (AMS) ions and compounds found in 50-nm filter samples with traditional gas chromatography MS (GC-MS) and liquid chromatography MS (LC-MS) analysis with all possible positive correlations at r P 0.7 (Reprinted with permission from [12]).
identified in mixed spectra (PAHs, hydrocarbons, elemental carbon, levoglucosan) [9,19,48]. As pointed out in section 2.3, the challenge is to increase the amount of information that can be extracted from the MS data, whether this will be through use of soft-ionization, highresolution MS2, or additional separation steps. The various chemometric tools now available are also increasingly being applied [12,53] to reveal correlations between the MS data and chemical, physical, and meteorological parameters (Fig. 6). Other analytical techniques (GC-MS and LC-MS) for off-line collected and extracted aerosol samples can be used to provide supporting information for fuller characterization of the AMS results, as shown in Fig. 6 as correlations between the masses found in AMS and compounds identified with other techniques [12]. In general, still too little is known about the individual organic compounds present in aerosols. With their larger size, bioaerosols represent a special area of AMS applications. Bioaerosols include different viruses, bacteria, and pollen. Since viruses and bacteria are potentially biological weapons, an urgent search is underway for reliable monitoring techniques [41,47]. AMS would appear to be an excellent tool for the purpose. Recently, an instrument was successfully developed and tested for detection of hazardous aerosols at airports. Aerosol particles are sampled, focused, tracked,
sized, analyzed for fluorescence and charge, and finally mass analyzed with a dual-polarity mass spectrometer [45].
References [1] R.A. Ketola, T. Kotiaho, M.E. Cisper, T.M. Allen, J. Mass Spectrom. 37 (2002) 457–476. [2] D.J. Butcher, Microchem. J. 66 (2000) 55–72. [3] M. Hallquist, J.C. Wenger, U. Baltensperger, Y. Rudich, D. Simpson, M. Claeys, J. Dommen, N.M. Donahue, C. George, A.H. Goldstein, J.F. Hamilton, H. Herrmann, T. Hoffmann, Y. Iinuma, M. Jang, M.E. Jenkin, J.L. Jimenez, A. Kiendler-Scharr, W. Maenhaut, G. McFiggans, Th.F. Mentel, A. Monod, A.S.H. Pre´voˆt, J.H. Seinfeld, J.D. Surratt, R. Szmigielski, J. Wildt, Atmos. Chem. Phys. 9 (2009) 5155–5236. [4] S.J. Hanna, P. Campuzano-Jost, E.A. Simpson, D.B. Robb, I. Burak, M.W. Blades, J.W. Hepburn, A.K. Bertram, Int. J. Mass Spectrom. 279 (2009) 134–146. [5] M. Brands, M. Kamphus, T. Boumlttger, J. Schneider, F. Drewnick, A. Roth, J. Curtius, C. Voigt, A. Borbon, M. Beekmann, A. Bourdon, T. Perrin, S. Borrmann, Aerosol Sci. Technol. 45 (2011) 46–64. [6] Y. Gao, W.A. Hall IV, M.V. Johnston, Environ. Sci. Technol. 44 (2010) 7897–7902. [7] A.C. Aiken, P.F. DeCarlo, J.H. Kroll, D.R. Worsnop, J.A. Huffman, K.S. Docherty, I.M. Ulbrich, C. Mohr, J.R. Kimmel, D. Sueper, Y. Sun, Q. Zhang, A. Trimborn, M. Northway, P.J. Ziemann, M.R. Canagaratna, T.B. Onasch, M.R. Alfarra, A.S.H. Prevot, J. Dommen, J. Duplissy, A. Metzger, U. Baltensperger, J.L. Jimenez, Environ. Sci. Technol. 42 (2008) 4478–4485.
http://www.elsevier.com/locate/trac
1495
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
[8] P.F. DeCarlo, J.R. Kimmel, A. Trimborn, M.J. Northway, J.T. Jayne, A.C. Aiken, M. Gonin, K. Fuhrer, T. Horvath, K.S. Docherty, D.R. Worsnop, J.L. Jimenez, Anal. Chem. 78 (2006) 8281–8289. [9] R. Holzinger, A. Kasper-Giebl, M. Staudinger, G. Schauer, T. Ro¨ckmann, Atmos. Chem. Phys. Discuss. 10 (2010) 13969– 14011. [10] L. Li, Z. Huang, J. Dong, M. Li, W. Gao, H. Nian, Z. Fu, G. Zhang, X. Bi, P. Cheng and Z. Zhou, Int. J. Mass Spectrom. (2011), in press, doi:10.1016/j.ijms.2011.01.017. [11] T. Laitinen, K. Hartonen, M. Kulmala, M.-L. Riekkola, Boreal Env. Res. 14 (2009) 539–549. [12] T. Laitinen, M. Ehn, H. Junninen, J. Ruiz-Jimenez, J. Parshintsev, K. Hartonen, M.-L. Riekkola, D.R. Worsnop, M. Kulmala, Atmos. Environ. 45 (2011) 3711–3719. [13] A. Faccinetto, P. Desgroux, M. Ziskind, E. Therssen, C. Focsa, Combustion and Flame 158 (2011) 227–239. [14] J.-H. Xing, K. Takahashi, A. Yabushita, T. Kinugawa, T. Nakayama, Y. Matsumi, K. Tonokura, A. Takami, T. Imamura, K. Sato, M. Kawasaki, T. Hikida, A. Shimono, Aerosol Sci. Technol. 45 (2011) 315–326. [15] C.B. Robinson, J.R. Kimmel, D.E. David, J.T. Jayne, A. Trimborn, D.R. Worsnop, J.L. Jimenez, Int. J. Mass Spectrom. 303 (2011) 164–172. [16] S. Wang, M.V. Johnston, Int. J. Mass Spectrom. 258 (2006) 50– 57. [17] S. Geddes, B. Nichols, S. Flemer Jr., J. Eisenhauer, J. Zahardis, G.A. Petrucci, Anal. Chem. 82 (2010) 7915–7923. [18] B.W. LaFranchi, G.A. Petrucci, Int. J. Mass Spectrom. 258 (2006) 120–133. [19] B. O¨ktem, M.P. Tolocka, M.V. Johnston, Anal. Chem. 76 (2004) 253–261. [20] H. Hellen, J. Dommen, A. Metzger, A. Gascho, J. Duplissy, T. Tritscher, A.S.H. Prevot, U. Baltensperger, Environ. Sci. Technol. 42 (2008) 7347–7353. [21] D.G. Nash, X.F. Liu, E.R. Mysak, T. Baer, Int. J. Mass Spectrom. 241 (2005) 89–97. [22] A.N. Martin, G.R. Farquar, P.T. Steele, A.D. Jones, M. Frank, Anal. Chem. 81 (2009) 9336–9342. [23] E.A. Simpson, P. Campuzano-Jost, S.J. Hanna, D.B. Robb, J.H. Hepburn, M.W. Blades, A.K. Bertram, Int. J. Mass Spectrom. 281 (2009) 140–149. [24] J.N. Smith, K.C. Barsanti, H.R. Friedli, M. Ehn, M. Kulmala, D.R. Collins, J.H. Scheckman, B.J. Williams, P.H. McMurry, PNAS 107 (2010) 6634–6639. [25] K.R. Wilson, M. Jimenez-Cruz, C. Nicolas, L. Belau, S.R. Leone, M. Ahmed, J. Phys. Chem. A 110 (2006) 2106–2113. [26] H. Tervahattu, J. Juhanoja, V. Vaida, A.F. Tuck, J.V. Niemi, K. Kupiainen, M. Kulmala, H. Vehkama¨ki, J. Geophys. Res. 110 (2005) D06207. doi:10.1029/2004JD005400. [27] M. Haapala, J. Po´l, V. Saarela, V. Arvola, T. Kotiaho, R.A. Ketola, S. Franssila, T.J. Kauppila, R. Kostiainen, Anal. Chem. 79 (2007) 7867–7872. [28] D.R. Ifa, C. Wu, Z. Ouyangbc, R.G. Cooks, Analyst 135 (2010) 669–681. [29] Y. Gao, M.V. Johnston, Rapid Commun. Mass Spectrom. 23 (2009) 3963–3968. [30] E. Gard, J.E. Mayer, B.D. Morrical, T. Dienes, D.P. Fergenson, K.A. Prather, Anal. Chem. 69 (1997) 4083–4091.
1496
http://www.elsevier.com/locate/trac
[31] E.S. Cross, J.G. Slowik, P. Davidovits, J.D. Allan, D.R. Worsnop, J.T. Jayne, D.K. Lewis, M. Canagaratna, T.B. Onasch, Aerosol Sci. Technol. 41 (2007) 343–359. [32] S. Geddes, J. Zahardis, J. Eisenhauer, G.A. Petrucci, Int. J. Mass Spectrom. 282 (2009) 13–20. [33] X. Wang, P.H. McMurry, Int. J. Mass Spectrom. 258 (2006) 30–36. [34] W.H. Benner, M.J. Bogan, U. Rohner, S. Boutet, B. Woods, M. Frank, Aerosol Sci. 39 (2008) 917–928. [35] M.J. Northway, J.T. Jayne, D.W. Toohey, M.R. Canagaratna, A. Trimborn, K.-I. Akiyama, A. Shimono, J.L. Jimenez, P.F. DeCarlo, K.R. Wilson, D.R. Worsnop, Aerosol Sci. Technol. 41 (2007) 828– 839. [36] L. Zhou, K. Park, H.M. Milchberg, M.R. Zachariah, Aerosol Sci. Technol. 41 (2007) 818–827. [37] A. Zelenyuk, J. Yang, D. Imre, Int. J. Mass Spectrom. 282 (2009) 6–12. [38] A.A. Specht, M.W. Blades, J. Am. Soc. Mass Spectrom. 14 (2003) 562–570. [39] H. Tervahattu, K. Hartonen, V.-M. Kerminen, K. Kupiainen, P. Aarnio, T. Koskentalo, A.F. Tuck, V. Vaida, J. Geophys. Res. 107 (2002) D7 AAC 1/1–AAC 1/9. [40] P.J. Silva, M.E. Erupe, D. Price, J. Elias, Q.G.J. Malloy, Q. Li, B. Warren, D.R. Cocker III, Environ. Sci. Technol. 42 (2008) 4689– 4696. [41] H.J. Tobias, M.P. Schafer, M. Pitesky, D.P. Fergenson, J. Horn, M. Frank, E.E. Gard, Appl. Environ. Microbiol. 71 (2005) 6086– 6095. [42] M.J. Bogan, E. Patton, A. Srivastava, S. Martin, D.P. Fergenson, P.T. Steele, H.J. Tobias, E.E. Gard, M. Frank, Rapid Commun. Mass Spectrom. 21 (2007) 1214–1220. [43] M. DallÕOsto, R.M. Harrison, E. Charpantidou, G. Loupa, S. Rapsomanikis, Sci. Total Environ. 384 (2007) 120–133. [44] I.-K. Lee, M. Winterer, Rev. Sci. Instrum. 76 (2005) 095104. [45] P.T. Steele, G.R. Farquar, A.N. Martin, K.R. Coffee, V.J. Riot, S.I. Martin, D.P. Fergenson, E.E. Gard, M. Frank, Anal. Chem. 80 (2008) 4583–4589. [46] S. Geddes, B. Nichols, K. Todd, J. Zahardis, G.A. Petrucci, Atmos. Meas. Tech. 3 (2010) 1175–1183. [47] D.P. Fergenson, M.E. Pitesky, H.J. Tobias, P.T. Steele, G.A. Czerwieniec, S.C. Russell, C.B. Lebrilla, J.M. Horn, K.R. Coffee, A. Srivastava, S.P. Pillai, M.-T.P. Shih, H.L. Hall, A.J. Ramponi, J.T. Chang, R.G. Langlois, P.L. Estacio, R.T. Hadley, M. Frank, E.E. Gard, Anal. Chem. 76 (2004) 373–378. [48] M. Bente, M. Sklorz, T. Streibel, R. Zimmermann, Anal. Chem. 80 (2008) 8991–9004. [49] W.A. Harris, P.T.A. Reilly, W.B. Whitten, Anal. Chem. 79 (2007) 2354–2358. [50] T. Hohaus, D. Trimborn, A. Kiendler-Scharr, I. Gensch, W. Laumer, B. Kammer, S. Andres, H. Boudries, K.A. Smith, D.R. Worsnop, J.T. Jayne, Atmos. Meas. Tech. 3 (2010) 1423–1436. [51] H. Junninen, M. Ehn, T. Peta¨ja¨, L. Luosuja¨rvi, T. Kotiaho, R. Kostiainen, U. Rohner, M. Gonin, K. Fuhrer, M. Kulmala, D.R. Worsnop, Atmos. Meas. Tech. 3 (2010) 1039–1053. [52] M. Ehn, H. Junninen, T. Peta¨ja¨, T. Kurte´n, V.-M. Kerminen, S. Schobesberger, H.E. Manninen, I.K. Ortega, H. Vehkama¨ki, M. Kulmala, D.R. Worsnop, Atmos. Chem. Phys. 10 (2010) 8513– 8530. [53] S.M. Toner, L.G. Shields, D.A. Sodeman, K.A. Prather, Atmos. Environ. 42 (2008) 568–581.
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Current instrumentation for aerosol mass spectrometry Kari Hartonen, Totti Laitinen, Marja-Liisa Riekkola This review describes recently presented instrumental set-ups for aerosol mass spectrometry (AMS), most being suitable for in-situ analysis. AMS allows the analysis of atmospheric aerosol particles within a short time interval and without sample pretreatment, and it is less sensitive to artifact formation than conventional sampling and analytical techniques. Although a quantitative measure of total organic loading can be obtained with some AMS instruments, they currently give only limited information on specific compounds. When the ionization technique produces a large number of fragments for a compound, it becomes impossible to track the original compound. Moreover, at present, there is no commercially available instrument capable of quantitative analysis of chemical compounds in ambient aerosol particles with diameters of 0.003–50 lm and simultaneously offering short time resolution. We pay special attention to the technical and methodological challenges of AMS, whose benefits we demonstrate with selected applications. ª 2011 Elsevier Ltd. All rights reserved. Keywords: Aerosol mass spectrometry; Aerosol particle; Desorption; Detection; Fragment; In-situ analysis; Instrumentation; Ionization; Mass analyzer; Particle size
1. Introduction Kari Hartonen*, Totti Laitinen, Marja-Liisa Riekkola University of Helsinki, Department of Chemistry, Laboratory of Analytical Chemistry, P.O. Box 55, FI-00014, Finland
*
Corresponding author. Tel.: +358 919 150 265; Fax: +358 919 150 253; E-mail: [email protected], [email protected], [email protected]
1486
Mass spectrometry (MS) is well suited for the direct analysis of gas and particle phases in air, thanks to the fast response, excellent sensitivity, and qualitative (structural) information provided. Moreover, MS can be regarded as a universal detector with the potential for highly selective mode of operation. Direct monitoring and analysis of gas-phase compounds is relatively straightforward, since samples are easily introduced through a membrane inlet or as a small gas flow into the ionization chamber of the MS [1,2]. Aerosols (suspended solid or liquid particles in gas phase) are of major interest today because of their impact on human health and their tendency to cool the EarthÕs climate (although aerosols, containing, for example, black carbon, can have the opposite effect). The effect that aerosols have greatly depends on their size, chemical composition, and concentration. Some aerosols, for example, contain dangerous species (e.g., microbiological, biological, and chemical toxins), which are a threat to human health. In particular, very fine particles are able to penetrate deep into the respiratory system. Size segregation (or particle-size informa-
tion) is usually essential in MS investigations of atmospheric aerosols. Not only does the relative portion of organic matter tend to increase with decreasing size of the particles, but our understanding of aerosol formation and growth processes, so critical in climate studies, depends upon resolving the chemical composition of ultra-fine nucleation particles [3]. Conventionally, aerosol particles have been collected onto filters and extracted with organic solvent to release compounds for analysis. This approach has several drawbacks (e.g., the long collection time may lead to alteration of the compounds through oxidation, gas-phase compounds may be absorbed or adsorbed, and volatiles may be lost). Moreover, the study of short-lived processes is not possible because of poor time resolution of the data (long collection time needed to obtain sufficient amount of analytes for detection). Although sensitive on-line MS analysis allows real-time or near-real-time measurement, it is essential in MS analysis of aerosols that compounds are first vaporized or desorbed from particles into gas phase and then ionized. Usually, the particles are size separated before these two steps, so that information on chemical
0165-9936/$ - see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2011.06.007
Instrument AMS with two-step laser desorption and ionization Laser-ablation AMS (ALABAMA)
Sample
Desorption
Single particle
TEA-CO2 laser
Single particle
UV laser, 266 nm (ablation + ionization), 2.5 · 108 W/cm2, 2.6 · 109 W/cm2* Solvent desorption (extraction)
Ionization Tunable VUV laser, 122– 168 nm UV laser, 266 nm (ablation + ionization), 2.5 · 108 W/cm2, 2.6 · 109 W/cm2* Electrospray ionization (ESI)
Mass analyzer
Particle size
Ion trap (IT)
P 300 nm
Caffeine aerosol particles, gas-phase compounds
Bipolar-TOF
150–900 nm
Measurement of organic and inorganic compounds during MEGAPOLI 2009 campaign (Paris)
FT-ICR, QTOF API-US
6500 nm
Secondary organic aerosols (SOA) from the ozonolysis of monoterpenes in flowtube reactor Primary, secondary, ambient organic aerosols. Ambient aerosol SOAR-1 study in Riverside, CA, USA; MIRAGE C-130 aircraft study near Mexico City. Atomic ratios O/C, H/ C, N/C, and OM/OC Quantitative analysis of ambient organic compounds
http://www.elsevier.com/locate/trac
High-resolution FTICR-MS, nanoaerosol MS (NAMS)
Particle collection (2– 120 h)
High-resolution TOF-AMS
Single particle
Thermal vaporization at ca. 600C
Electron impact (EI)
TOF
35 nm–1.5 lm
High-mass resolution thermal desorption (TD) PTR-MS
Particle collection
Thermal desorption up to 350C
Chemical ionization (CI)
TOF
Humidified atmospheric particles <2.5 lm
Laser desorption/ ionization TOF-MS
Single particle
UV laser 266 nm*
UV laser 266 nm*
TOF
250 nm–2 lm
Two-step laser desorption-ionization AMS
Particle collection (electrostatic deposition)
IR laser 1064 nm
UV laser 193 nm
TOF
19, 30 and 22 nm, 10– 50 nm
Laser desorption (LD) Particle and laser ionization (LI) collection TOF-MS
Vis laser 532 nm (ca.5 MW/cm2)
UV laser 266 nm (1–2 MW/cm2)
TOF
Gases and particles of all sizes
Laser desorption/ ionization (LISPA)AMS
UV laser 248 nm (107 W/cm2)*
UV laser 248 nm (107 W/cm2)*
TOF
250 nm–1.3 lm
Single particle
Application
Comments
Ref.
No sample preparation, good [4] sensitivity, and selective ionization Small, handy instrument, [5] aircraft measurements
High mass resolution and good identification, comparison with LC-MS
[6]
High resolution for rapid [7,8] single particle analysis in real-time (detection limits for sub-lm aerosol <0.04 lg/m3 in the high-sensitivity mode and <0.4 lg/m3 in the highresolution mode)
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Table 1. Aerosol mass spectrometry (AMS) instrumentation used in aerosol research
High-resolution TOF-MS. [9] Transfer line from TD unit to PTR-MS at 180C. Comparison with OC from filter sampling Polystyrene latex particles [10] and metallic solution used to perform size and mass calibration
1487
Trends
Ambient aerosols in Guangzhou City, China, classification of aerosols into different groups by their chemical composition Self-generated particles, Sample collection at [11,12] ambient particles, black atmospheric pressure, rapid carbon, and liquid samples sample introduction to MS vacuum via special sampling valve Chemical composition Flame studies of soot [13] (PAHs) of soot particles formation process with filter sampled from a lowcollection. Soft ionization in pressure flame MS Characterization of aerosol Good correlation with [14] particles in Tokyo, Japan Aerodyne AMS; ammonium, sulfate and organic compounds detected (continued on next page)
Trends
1488 Table 1. (continued) http://www.elsevier.com/locate/trac
Instrument
Sample
Desorption
Ionization
Mass analyzer
Particle size
Application
Comments
Ref.
Design of metastable atombombardment ionization for AMS, MAB compared with EI and VUV Nanoparticle detection and identification at elemental level; test nanoparticles produced from several pure chemicals
Sensitive ionization with less fragmentation, real-time alternation between MAB and EI Atomic composition from studied compounds, particles trapped inside ion trap for laser ablation followed by TOF-MS analysis Very sensitive instrument suitable for near-real-time study of particle formation and growth, LOD 89 fg for pinic acid and 8.8 pg for cholesterol Soft ionization method, suited for the analysis of particle-phase and gas-phase organics
[15]
Single particle
Thermal desorption
Metastable atom bombardment (MAB), EI
TOF
P 35 nm
Particle collection inside ion trap (IT)
Ablation with Vis laser 532 nm (160 mJ)*
Ablation with Vis laser 532 nm (160 mJ)*
TOF
<30 nm
Near-infrared (NIR) laser desorption/ ionization (LDI) AMS
Particle collection
NIR laser 1064 nm (80 MW/cm2)*
NIR laser 1064 nm (80 MW/cm2)*
TOF
180 nm on average
Detection of primary and secondary organics in chamber studies
Photoelectron resonance capture ionization (PERCI)AMS
Particle collection
Thermal vaporization probe (up to 400C)
TOF
50–380 nm
Photoionization AMS (PIAMS)
Particle collection
IR laser, 1064 nm
UV laser, 235– 300 nm (100 mJ/ cm2) focused to aluminum photoelectrode UV laser, 118 nm
TOF
<300 nm
Quantitative analysis of organics from aerosols pneumatically generated from dilute standard solutions Organics on fine and ultrafine particles
Proton-transferreaction MS (PTR-MS)
Single particle
Thermal vaporization at 120/150C
Chemical ionization (CI)
Quadrupole
0.52 20 lm
AMS with VUV radiation generated by resonance difference frequency mixing (RDFM)
Single particle
IR laser or impaction on heater
VUV laser, 142 nm (with RDFM) or 118 nm
TOF
Micrometer range
Laser desorption/ ionization AMS (SPAMS)
Single particle
UV laser, 266 nm (2.4 or 2.7 nJ/ lm2)*
UV laser, 266 nm (2.4 or 2.7 nJ/ lm2)*
Bipolar-TOF
Micrometer range
Drug identification from multi-component tablets
ITMS with laser desorption and EI ionization (SPIT-MS)
Single particle
IR laser, 10.6 lm (50 mJ/5 · 107 W/ cm2)
Electron impact (EI)
Ion trap (IT)
0.1–1.1 lm
Laboratory-generated pure aerosols (caffeine, oleic acid, linoleic acid, dihydroxybenzoic acid)
Chamber measurements for secondary organic aerosol (SOA), pinonic acid particles Detection of oleic acid with minimal fragmentation
Selective desorption on the collection probe, soft ionization Gas-phase analysis. Also suitable for on-line secondary organic aerosol (SOA) analysis RDFM producing less fragmentation and more intensive molecular ion for oleic acid. More homogeneous heating with heater than with IR (CO2) laser. Excellent S/N ratio Fast, non-destructive method for drug screening from multi-component samples, no need for sample pretreatment MS2 possibility and EI ionization. Vaporization and ionization inside the ion trap, high sensitivity
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Thermal desorptionmetastable atom bombardment ionization (MAB)-AMS Nanoaerosol mass spectrometer (NAMS)
[25] Introduction of fragile biomolecules to gas phase as nanoparticles and their fragment-free photoionization 70–1000 nm
One laser used for both desorption and ionization.
2. Instrumental solutions for aerosol mass spectrometry
*
TOF Single particle Vacuum-UV-AMS
Thermal vaporization (298–873 K)
UV laser (tunable, 7–25 eV)
3 nm–2 lm Triple quadrupole Chemical ionization (CI) Thermal desorption (up to 500C) Particle collection Thermal desorption and chemical ionization MS (TDCIMS)
Trends
composition can be obtained as a function of particle size. Aerosol MS (AMS) techniques can usefully be divided into two groups: those analyzing single particles, and those analyzing many particles of a certain size collected over a short period of time. Whatever the sampling system, direct MS analysis will always produce mixed spectra of the many components present in the aerosols (aerosols of pure compounds are excluded). Chemometric tools for data analysis and use of tandem MS (MS2) techniques are an invaluable assistance for resolving the complex spectral information. High mass resolution can facilitate the analysis by providing possible molecular formulas for the ions, and softer ionization techniques will provide less fragmentation and less complex spectra for interpretation (or molecular ions suitable for MS2 characterization). Particles collected off-line on surfaces (e.g., filters or impactor plates) can be analyzed by MS using desorption techniques {e.g., SIMS [26]} and novel ambient desorption/ionization techniques {e.g., DAPPI [27] or DESI [28]}. Although, in the strict sense, these are not AMS techniques, with a short enough collection period, they could perhaps be applied in on-line, near-real-time aerosol analysis, and they might be used for the detection of compounds present in high abundance. They could also be applied as alternatives to the laser or thermal desorption generally used in AMS. On-line aerosol-particle analysis has already been successfully performed with matrix-assisted laser desorption ionization (MALDI), where an aerodynamic lens system is applied to focus the aerosol beam onto a MALDI target plate [29]. We describe below various AMS systems and approaches enabling in-situ analysis of atmospheric aerosols within a short time interval and without sample pretreatment. We cover selected applications in the final section.
Detection of aminium salts in atmospheric nanoparticles. Measurements in Mexico City and in the boreal forest at Hyytia¨la¨, Finland Biological nanoparticles (from amino acids and polypeptides)
Aminium-salt formation found to be widespread and could account for a significant part of nanoparticle growth
[24]
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Many different AMS set-ups are possible, varying with the type of aerosol inlet, aerosol sizing, desorption, ionization, and MS-analyzer system employed. There are two commercial AMS systems (TSI and Aerodyne) but the first is no longer available on the market. The TSI system comprises a nozzle-skimmer system for aerosol inlet, lasers for particle-velocity measurement and sizing, and a laser for desorption/ ionization before the bipolar time-of-flight (TOF) MS measurement. The system is based on the ATOFMS design of Gard et al. [30]. The second (Aerodyne) utilizes an aerodynamic lens system for particle-beam focusing, a chopper to pulse the beam onto the thermal desorption surface, followed by electron-impact (EI) ionization before MS analysis [7]. In this system, particle size is http://www.elsevier.com/locate/trac
1489
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
deduced from the flight time of the particle between the chopper and the detector (a sizing system with light scattering of laser radiation has been demonstrated [31]). Several commercial models of the second system exist, with different MS analyzers incorporated (quadrupole and TOF with different resolution). Besides commercial instruments, many self-made AMS constructions and set-ups have been described, and these are the focus of this review. Table 1 summarizes selected technical solutions and variations for AMS instrumentation. 2.1. Aerosol sampling and size separation In AMS systems, air particles are typically sampled through a small orifice, usually ca. 100 lm, resulting in 80–90 mL/min flow into vacuum (1.6–3 Torr) [16,19,23]. In some studies, orifices of 80 lm [10] and even 260 lm [32] have been employed. In the latter case, the air flow into the vacuum system was as high as 500 mL/min. The flow-limiting critical orifice leading into the vacuum system allows the aerosol flow to be focused by an aerodynamic lens system. In general, the aerodynamic lens system is used to focus aerosols from ca. 0.040–1 lm into a very tight beam, though transmission efficiency is close to 100% only for particles in the 60–600-nm range. Efficiency drops off noticeably for smaller and larger particles (e.g., 25% efficiency for 1 lm) [5]. Fortunately, however, the lens system can be designed and optimized for nanoparticle transmission, as has been successfully done for 3–30 nm particles [33]. The aerodynamic lens system is definitely the most popular choice for particle-beam focusing (into a point where particle collection or desorption/ionization of a single particle will occur). From the aerodynamic lens system, the particles pass through a nozzle that controls the supersonic gas expansion into high vacuum. Particle velocities are in the range of 50–400 m/s [23]. Velocity (and size) is generally determined by the detection of scattered light by two laser–photomultiplier tube (PMT) pairs located at a fixed distance from each other. Laser of wavelength 532 nm is the most common for particle detection and sizing {typically on the order of 100 mW/ cm2 [23]}. As many as six laser–PMT pairs have been used to track the particles after air flow through a converging nozzle into differentially pumped vacuum and particle focusing [22]. As a replacement for lasers, Benner et al. [34] developed a single-particle image-charge detector for their AMS to measure the velocity and thereby the size of particles. Both particle size and velocity need to be known in order to hit a single particle with a desorption/ ionization laser. However, since particles smaller than ca. 100 nm do not scatter light, desorption/ionization of a single particle in this size range becomes a question of luck. There are only a few AMS systems that do not make use of the aerodynamic lens. One system exploited var1490
http://www.elsevier.com/locate/trac
ious pre-cut-offs in front of the inlet (for different size fractions) [9], and the increase in the aerosol-collection flow from 0.9 L/min to 9 L/min was found to improve the sensitivity 10-fold. In another approach, particles were charged, after which a differential mobility analyzer (DMA) was utilized for the size separation [11]. In this latter set-up, the charged and size-separated particles were collected via electrostatic deposition on a surface of the sampling valve working as an interface between the atmospheric collection and high MS vacuum. 2.2. Desorption and ionization Compounds in aerosol particles are most frequently desorbed through a quick temperature increase (vaporization). Single particles are directed toward a hot surface and flash vaporized in the vicinity of the surface. Alternatively, particles can be collected onto the surface for a short time and then desorbed through resistive heating of the surface (fast thermal desorption). Heating and desorption can also be achieved by a short pulse from an IR laser. For single-particle analysis, the laser beam needs to be well timed, aligned, and focused in order to hit the arriving particle. Timing is less critical for those AMS systems that utilize collection on a surface close in size to that of the laser beam (a few mm in diameter), but still the laser beam needs to be positioned well. Fig. 1 shows an example of thermal desorption with a vaporization probe where the coiled Nichrome filament can be resistively heated up to 400C to vaporize the particles. Alternatively, the probe can be operated at constant temperature (400C) to flash vaporize the incoming single particles. Desorbed compounds are ionized by a laser generating photoelectrons from an aluminum photocathode [18]. Interestingly, one of the commercial AMS instruments (Aerodyne) has also been modified by the addition of metastable-atom bombardment (MAB) ionization (Fig. 2). After flash vaporization near the hot surface (typically 600C), the vapor plume is ionized by either EI or MAB. In MAB, argon, krypton or nitrogen was employed as discharge gas [15]. Less fragmentation of organic compounds was produced by MAB than by EI, at least at the lower vaporization temperature of 180C. Also, a vacuum-UV lamp with 2 mm i.d. and MgF2 window has been successfully connected to one side of the AMS vaporization and ionization region just 9 mm from the center of the heated vaporization surface. Less fragmentation is achieved through sensitive photoionization, as was clearly demonstrated for pristine [35]. Lasers are frequently applied for desorption and ionization due to the high sensitivity that they can provide, and the resulting soft photoionization with less fragmentation. The energetic lasers with pulses of a few ns that are typically used also fit well with TOF analyzers.
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Trends
Figure 1. (a) Photoelectron resonance capture ionization aerosol mass spectrometry (PERCI-AMS), which comprises five main components: (1) particle inlet; (2) particle collector/vaporization probe (VP); (3) aluminum photoelectrode (PE); (4) tunable UV pulsed laser; and, (5) time-of-flight mass spectrometer along with necessary electronics and data-processing equipment. (b) Close-up of ion-extraction region that includes photoelectrode, vaporization probe, and ion-extraction electrode (Reprinted with permission from [18]).
Figure 2. The metastable atom beam source coupled to the aerosol mass spectrometry (AMS) ionization region (Reprinted with permission from [15]).
Laser–particle interactions have been studied in some detail by Zhou et al. [36]. Selectivity of the lasers (especially in ionization) can be a benefit or a drawback. An IR laser is generally employed, at either 1064 nm or 10.6 lm wavelength, for desorption, while UV at 266 nm or vacuum-UV at 118 nm is the preferred laser for the ionization of molecules. Lasers are also used along with other desorption and ionization techniques. Use of two lasers requires that the timing (delay) between the lasers be carefully optimized. Fig. 3 shows a typical setup for AMS with two-step laser desorption (IR) and ionization (VUV) of a single particle. If a single laser pulse is used for desorption and ionization, typically the UV laser is utilized. With UV (266 nm) ablation at 2.5 · 108 W/cm2, the maximum ablation efficiency was 96% for 400-nm polystyrene
latex particles and >90% for the entire size range 240– 500 nm [5]. However, a more intense beam (2.6 · 109 W/cm2) was necessary for the ionization of NaCl particles. Zelenyuk et al. [37] have made a detailed comparison of UV ablation and IR-UV two-step laser desorption and ionization. Recently, a 532-nm laser was applied for desorption in soot analysis but the intensity was much higher than that used for detection and sizing of particles [13]. Fig. 4 illustrates an AMS system where a CO2 laser is used for particle desorption. The CO2 desorption laser enters at 35.2o angle between the ring and end cap to intersect with the particle beam (coming through a 2-mm hole in the ring electrode) in the center of the trap. For desorption, a 250-mm ZnSe lens focuses the output
http://www.elsevier.com/locate/trac
1491
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Figure 3. Single aerosol-particle laser time-of-flight (TOF) instrument. Particles are focused in the aerodynamic lens, detected and sized in the two light-scattering regions, then vaporized and ionized in the extraction region of the TOF mass spectrometer (TOF-MS) (Reprinted with permission from [21]).
Figure 4. Instrument set-up for ion trap mass spectrometry (IT-MS) using laser desorption and electron impact (EI) (Reprinted with permission from [23]).
of the CO2 laser to a spot ca. 1 mm in diameter inside the ion trap [23]. AMS-like systems with the particle collection outside the MS vacuum have been described. In one of these, the aerosol sample collected is kept in a preparation chamber at 160C before introduction to the MS through a gate valve [13]. In another system, before two-step laser desorption and ionization, the sample probe is inserted into the ion trap through the vacuum interlock without
1492
http://www.elsevier.com/locate/trac
breaking the vacuum [38]. Both these approaches employ the old direct-insertion probe (DIP) concept, as does a solution that collects aerosol particles on a filter and makes use of thermal desorption and EI before MS analysis [39]. 2.3. Mass-spectrometry analysis Direct analysis of compounds in aerosol particles by MS always results in a mixed spectrum (except for aerosols
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Trends
Figure 5. High-resolution time-of-flight aerosol mass spectrometry (TOF-AMS) with reflectors (Reprinted with permission from [8]).
generated from pure compounds), and interpretation of the spectrum is challenging. The amount of reliable chemical information obtained (e.g., from air particles) is minimal. Several different techniques have been enlisted in the attempt to overcome this problem, namely: (1) softer and more selective ionization (discussed above); (2) high mass resolution; (3) MS2; and, (4) separation of compounds before MS. Fig. 5 depicts an AMS instrument with one (V mode) or three (W mode) reflections applied for the ion beam in a TOF analyzer. With m/z of 200, the mass resolution obtained was 2100 for V mode and 4300 for W mode [8]. Similarly, higher mass resolution (3500– 5000) has been used with proton transfer reaction (PTR)–TOF-MS in an attempt to squeeze more information from the spectral data (to access the molecular formulas of the ions) [9]. Nevertheless, the resolution obtained in these two studies was not of the quality (<5 ppm accuracy) generally required for molecular formula assignment. With use of FTICR-MS, Gao et al. [6] achieved excellent mass resolution for compounds in secondary organic aerosols (SOA), and reliable identification of compounds was also obtained by MS2 analysis. The ion trap (IT) is a good choice for the AMS analyzer, since it allows MS2 analysis. However, there are some drawbacks that limit its efficiency: (1) the total number of ions that can be stored simultaneously is limited by space charge; and, (2) the trapping efficiency for externally introduced ions is sometimes low. These two limitations were minimized in a set-up where separate lasers were employed for particle desorption and ionization in the center of the IT [38]. An aerodynamic lens system has been introduced with
minimal modification into the heated ion source of a commercial IT [49]. In addition, an IT has been employed for efficient trapping of 7–25 nm particles before TOF-MS analysis [16]. A separation step before MS has been incorporated in an aerosol-collection module and transfer line to gas chromatography–MS (GC-MS) for efficient characterization of SOA formed from b-pinene oxidation [50]. Preliminary measurements of ambient atmospheric aerosols were undertaken and the results presented. A technique closely related to AMS is atmospheric pressure interface (APi)-TOF-MS, which is used for the analysis of atmospheric ions and their clusters in realtime [51,52]. The instrument has been used for the detection of organosulfate, organic acids, inorganic acids (e.g., sulfuric acid) and their clusters, (poly)alkyl pyridines and (poly)alkyl amines. Although the instrument does not have an ionization source and detects only atmospheric ions, it can evidently be easily modified for the analysis of small particles. 3. Applications AMS is well suited for the on-line analysis of particulate matter in real time. It is deployable for field measurements in environmental studies and applicable for occupational health and safety investigations. Selected applications and the associated major findings are presented in Table 2. Many AMS applications have been designed for the investigation of different sizes of aerosol particles generated from pure compounds [11,16–18,21,23]. Typically, the studies on pure compounds involve the testing of instrumental performance, optimization of the instrumental conditions, and method development. Nevertheless, most AMS applications are aimed at the real task of resolving the chemical composition of
http://www.elsevier.com/locate/trac
1493
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Table 2. Selected different applications of aerosol mass spectrometry (AMS) and the results obtained Particle type, analytes Amines (trimethylamine) in fine particulate matter
Individual airborne, micron-sized, Mycobacterium tuberculosis H37Ra particles
Single micrometer-sized particles containing poly(ethylene glycol) (PEG)
Indoor airborne particles, tobacco smoke, insect repellents N,N-diethyl-3-methylbenzamide, bioallethrin, and piperonyl butoxide Silicon-carbide nanoparticles formed by thermal decomposition of tetramethylsilane
Actual or surrogate chemical, biological, radiological, nuclear, and explosive materials and illicit-drug precursors in aerosols Secondary organic aerosols from ozonolysis of apinene Aerosol particles in the Tokyo metropolitan area during summer 2008
Organic aerosols in Austrian Alps. Total of 638 mass peaks (18–392 Da) detected and quantified
Individual airborne cells in bioaerosols
Aerosol particles from diesel-car exhaust and wood combustion
Chemical warfare (CW)-related species in complex aerosol particles
Results
Ref.
Amines in fine particles were detected and quantified during ambient studies of winter inversions. Reaction rate of trimethylamine and nitrate radical was estimated at 4.4 · 10 16 cm3/molecules/s with a conversion rate to the aerosol phase of ca. 65%. Amines can contribute to SOA formation in areas where nitrate radical is a significant player in oxidation chemistry Using a distinct biomarker, the mass spectral signatures for aerosolized M. tuberculosis H37Ra particles were found to be distinct from those of particles of M. smegmatis, Bacillus atrophaeus, and B. cereus. For the first time, a potentially unique biomarker was measured in M. tuberculosis H37Ra at the single-cell level Optimization of bioaerosol mass spectrometer for complex biological samples, including human effluents. PEGs of average molecular mass >500 Da were detected in particles. Tripeptide tyrosine-tyrosine-tyrosine or 2,5dihydroxybenzoic acid was added as matrix to nebulized solutions to assist LDI with 266 nm or 355 nm laser, respectively Specific outdoor particles (e.g., dust and carbon particles) were detected in indoor air. Three main categories describing particles originating outdoors, in environmental tobacco smoke and in pesticides used indoor, were clearly distinguished With increasing temperature, particles formed and grew by coagulation. At higher temperatures, sintering of the particles became an important process. A simple model was used to compare the particle velocity in a molecular beam of AMS as a function of particle mass. The significant difference in the particle velocity could be explained by a change in the particle-shape factor due to sintering Laboratory experiment involving actual threat and surrogate releases mixed with ambient background aerosols showed broad-spectrum detection ability within seconds. Data from a field test at the San Francisco International Airport demonstrated extended field operation with an ultra-low false-alarm rate The limit of detection measured for pure oleic-acid particles (geometric mean diameter and standard deviation of 180 nm and 1.3 nm, respectively) was 140 fg (or 1.7 ng/m3/min sampling time) Spectra illustrated that approximately 95% of the oxygen-containing organic particles contained nitrate. Equivalent mass concentration of organic aerosol, traced by mass-to-charge ratio (m/z) 44, showed a close correlation with particulate nitrate and gas-phase odd oxygen, [O3+NO2], whereas equivalent mass concentration of organic aerosol, traced by m/z 57, did not Oxygenated hydrocarbons constituted the bulk of the aerosol mass (75%) followed by organic nitrogen compounds (9%), inorganic compounds (mostly NH3, 8%), unidentified/halogenated compounds (3.8%), hydrocarbons (2.7%), and organic sulfur compounds (0.8%) The mass spectral signature of individual Bacillus spores was characterized and the ability to distinguish two Bacillus spore species, B. thuringiensis and B. atrophaeus, was demonstrated It was demonstrated that the chemical profiles from different combustion sources (soft and hard wood combustion, gasoline and diesel car exhaust) can be well discriminated. Absolute detection limits in the zeptomole region were achieved for selected PAHs Observed semi-volatile species may have been chemisorbed on some particle surfaces in sub-monolayer concentrations and may remain hours after deposition. Identification of trace CW-agent-related species is feasible with this technique
[40]
atmospheric aerosols and investigating compound concentrations and the formation, growth, and fate of aerosols [5,7–10,12,14,24,40]. Often the results have been confirmed in reaction-chamber experiments [6,17,20], where similar reactions to those occurring in the atmosphere are simulated.
1494
http://www.elsevier.com/locate/trac
[41]
[42]
[43]
[44]
[45]
[46]
[14]
[9]
[47]
[48]
[49]
The typical compounds studied in atmospheric aerosols are ones arising from burning processes (e.g., PAHs) [13,48] and from reactions of biogenic compounds in the atmosphere (e.g., oxygenated terpene compounds) [9,46]. Usually some inorganic or total organic content is reported, or specific compounds that are easily
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
Trends
Figure 6. Sammon mapping correlation tree for laser aerosol mass spectrometry (AMS) ions and compounds found in 50-nm filter samples with traditional gas chromatography MS (GC-MS) and liquid chromatography MS (LC-MS) analysis with all possible positive correlations at r P 0.7 (Reprinted with permission from [12]).
identified in mixed spectra (PAHs, hydrocarbons, elemental carbon, levoglucosan) [9,19,48]. As pointed out in section 2.3, the challenge is to increase the amount of information that can be extracted from the MS data, whether this will be through use of soft-ionization, highresolution MS2, or additional separation steps. The various chemometric tools now available are also increasingly being applied [12,53] to reveal correlations between the MS data and chemical, physical, and meteorological parameters (Fig. 6). Other analytical techniques (GC-MS and LC-MS) for off-line collected and extracted aerosol samples can be used to provide supporting information for fuller characterization of the AMS results, as shown in Fig. 6 as correlations between the masses found in AMS and compounds identified with other techniques [12]. In general, still too little is known about the individual organic compounds present in aerosols. With their larger size, bioaerosols represent a special area of AMS applications. Bioaerosols include different viruses, bacteria, and pollen. Since viruses and bacteria are potentially biological weapons, an urgent search is underway for reliable monitoring techniques [41,47]. AMS would appear to be an excellent tool for the purpose. Recently, an instrument was successfully developed and tested for detection of hazardous aerosols at airports. Aerosol particles are sampled, focused, tracked,
sized, analyzed for fluorescence and charge, and finally mass analyzed with a dual-polarity mass spectrometer [45].
References [1] R.A. Ketola, T. Kotiaho, M.E. Cisper, T.M. Allen, J. Mass Spectrom. 37 (2002) 457–476. [2] D.J. Butcher, Microchem. J. 66 (2000) 55–72. [3] M. Hallquist, J.C. Wenger, U. Baltensperger, Y. Rudich, D. Simpson, M. Claeys, J. Dommen, N.M. Donahue, C. George, A.H. Goldstein, J.F. Hamilton, H. Herrmann, T. Hoffmann, Y. Iinuma, M. Jang, M.E. Jenkin, J.L. Jimenez, A. Kiendler-Scharr, W. Maenhaut, G. McFiggans, Th.F. Mentel, A. Monod, A.S.H. Pre´voˆt, J.H. Seinfeld, J.D. Surratt, R. Szmigielski, J. Wildt, Atmos. Chem. Phys. 9 (2009) 5155–5236. [4] S.J. Hanna, P. Campuzano-Jost, E.A. Simpson, D.B. Robb, I. Burak, M.W. Blades, J.W. Hepburn, A.K. Bertram, Int. J. Mass Spectrom. 279 (2009) 134–146. [5] M. Brands, M. Kamphus, T. Boumlttger, J. Schneider, F. Drewnick, A. Roth, J. Curtius, C. Voigt, A. Borbon, M. Beekmann, A. Bourdon, T. Perrin, S. Borrmann, Aerosol Sci. Technol. 45 (2011) 46–64. [6] Y. Gao, W.A. Hall IV, M.V. Johnston, Environ. Sci. Technol. 44 (2010) 7897–7902. [7] A.C. Aiken, P.F. DeCarlo, J.H. Kroll, D.R. Worsnop, J.A. Huffman, K.S. Docherty, I.M. Ulbrich, C. Mohr, J.R. Kimmel, D. Sueper, Y. Sun, Q. Zhang, A. Trimborn, M. Northway, P.J. Ziemann, M.R. Canagaratna, T.B. Onasch, M.R. Alfarra, A.S.H. Prevot, J. Dommen, J. Duplissy, A. Metzger, U. Baltensperger, J.L. Jimenez, Environ. Sci. Technol. 42 (2008) 4478–4485.
http://www.elsevier.com/locate/trac
1495
Trends
Trends in Analytical Chemistry, Vol. 30, No. 9, 2011
[8] P.F. DeCarlo, J.R. Kimmel, A. Trimborn, M.J. Northway, J.T. Jayne, A.C. Aiken, M. Gonin, K. Fuhrer, T. Horvath, K.S. Docherty, D.R. Worsnop, J.L. Jimenez, Anal. Chem. 78 (2006) 8281–8289. [9] R. Holzinger, A. Kasper-Giebl, M. Staudinger, G. Schauer, T. Ro¨ckmann, Atmos. Chem. Phys. Discuss. 10 (2010) 13969– 14011. [10] L. Li, Z. Huang, J. Dong, M. Li, W. Gao, H. Nian, Z. Fu, G. Zhang, X. Bi, P. Cheng and Z. Zhou, Int. J. Mass Spectrom. (2011), in press, doi:10.1016/j.ijms.2011.01.017. [11] T. Laitinen, K. Hartonen, M. Kulmala, M.-L. Riekkola, Boreal Env. Res. 14 (2009) 539–549. [12] T. Laitinen, M. Ehn, H. Junninen, J. Ruiz-Jimenez, J. Parshintsev, K. Hartonen, M.-L. Riekkola, D.R. Worsnop, M. Kulmala, Atmos. Environ. 45 (2011) 3711–3719. [13] A. Faccinetto, P. Desgroux, M. Ziskind, E. Therssen, C. Focsa, Combustion and Flame 158 (2011) 227–239. [14] J.-H. Xing, K. Takahashi, A. Yabushita, T. Kinugawa, T. Nakayama, Y. Matsumi, K. Tonokura, A. Takami, T. Imamura, K. Sato, M. Kawasaki, T. Hikida, A. Shimono, Aerosol Sci. Technol. 45 (2011) 315–326. [15] C.B. Robinson, J.R. Kimmel, D.E. David, J.T. Jayne, A. Trimborn, D.R. Worsnop, J.L. Jimenez, Int. J. Mass Spectrom. 303 (2011) 164–172. [16] S. Wang, M.V. Johnston, Int. J. Mass Spectrom. 258 (2006) 50– 57. [17] S. Geddes, B. Nichols, S. Flemer Jr., J. Eisenhauer, J. Zahardis, G.A. Petrucci, Anal. Chem. 82 (2010) 7915–7923. [18] B.W. LaFranchi, G.A. Petrucci, Int. J. Mass Spectrom. 258 (2006) 120–133. [19] B. O¨ktem, M.P. Tolocka, M.V. Johnston, Anal. Chem. 76 (2004) 253–261. [20] H. Hellen, J. Dommen, A. Metzger, A. Gascho, J. Duplissy, T. Tritscher, A.S.H. Prevot, U. Baltensperger, Environ. Sci. Technol. 42 (2008) 7347–7353. [21] D.G. Nash, X.F. Liu, E.R. Mysak, T. Baer, Int. J. Mass Spectrom. 241 (2005) 89–97. [22] A.N. Martin, G.R. Farquar, P.T. Steele, A.D. Jones, M. Frank, Anal. Chem. 81 (2009) 9336–9342. [23] E.A. Simpson, P. Campuzano-Jost, S.J. Hanna, D.B. Robb, J.H. Hepburn, M.W. Blades, A.K. Bertram, Int. J. Mass Spectrom. 281 (2009) 140–149. [24] J.N. Smith, K.C. Barsanti, H.R. Friedli, M. Ehn, M. Kulmala, D.R. Collins, J.H. Scheckman, B.J. Williams, P.H. McMurry, PNAS 107 (2010) 6634–6639. [25] K.R. Wilson, M. Jimenez-Cruz, C. Nicolas, L. Belau, S.R. Leone, M. Ahmed, J. Phys. Chem. A 110 (2006) 2106–2113. [26] H. Tervahattu, J. Juhanoja, V. Vaida, A.F. Tuck, J.V. Niemi, K. Kupiainen, M. Kulmala, H. Vehkama¨ki, J. Geophys. Res. 110 (2005) D06207. doi:10.1029/2004JD005400. [27] M. Haapala, J. Po´l, V. Saarela, V. Arvola, T. Kotiaho, R.A. Ketola, S. Franssila, T.J. Kauppila, R. Kostiainen, Anal. Chem. 79 (2007) 7867–7872. [28] D.R. Ifa, C. Wu, Z. Ouyangbc, R.G. Cooks, Analyst 135 (2010) 669–681. [29] Y. Gao, M.V. Johnston, Rapid Commun. Mass Spectrom. 23 (2009) 3963–3968. [30] E. Gard, J.E. Mayer, B.D. Morrical, T. Dienes, D.P. Fergenson, K.A. Prather, Anal. Chem. 69 (1997) 4083–4091.
1496
http://www.elsevier.com/locate/trac
[31] E.S. Cross, J.G. Slowik, P. Davidovits, J.D. Allan, D.R. Worsnop, J.T. Jayne, D.K. Lewis, M. Canagaratna, T.B. Onasch, Aerosol Sci. Technol. 41 (2007) 343–359. [32] S. Geddes, J. Zahardis, J. Eisenhauer, G.A. Petrucci, Int. J. Mass Spectrom. 282 (2009) 13–20. [33] X. Wang, P.H. McMurry, Int. J. Mass Spectrom. 258 (2006) 30–36. [34] W.H. Benner, M.J. Bogan, U. Rohner, S. Boutet, B. Woods, M. Frank, Aerosol Sci. 39 (2008) 917–928. [35] M.J. Northway, J.T. Jayne, D.W. Toohey, M.R. Canagaratna, A. Trimborn, K.-I. Akiyama, A. Shimono, J.L. Jimenez, P.F. DeCarlo, K.R. Wilson, D.R. Worsnop, Aerosol Sci. Technol. 41 (2007) 828– 839. [36] L. Zhou, K. Park, H.M. Milchberg, M.R. Zachariah, Aerosol Sci. Technol. 41 (2007) 818–827. [37] A. Zelenyuk, J. Yang, D. Imre, Int. J. Mass Spectrom. 282 (2009) 6–12. [38] A.A. Specht, M.W. Blades, J. Am. Soc. Mass Spectrom. 14 (2003) 562–570. [39] H. Tervahattu, K. Hartonen, V.-M. Kerminen, K. Kupiainen, P. Aarnio, T. Koskentalo, A.F. Tuck, V. Vaida, J. Geophys. Res. 107 (2002) D7 AAC 1/1–AAC 1/9. [40] P.J. Silva, M.E. Erupe, D. Price, J. Elias, Q.G.J. Malloy, Q. Li, B. Warren, D.R. Cocker III, Environ. Sci. Technol. 42 (2008) 4689– 4696. [41] H.J. Tobias, M.P. Schafer, M. Pitesky, D.P. Fergenson, J. Horn, M. Frank, E.E. Gard, Appl. Environ. Microbiol. 71 (2005) 6086– 6095. [42] M.J. Bogan, E. Patton, A. Srivastava, S. Martin, D.P. Fergenson, P.T. Steele, H.J. Tobias, E.E. Gard, M. Frank, Rapid Commun. Mass Spectrom. 21 (2007) 1214–1220. [43] M. DallÕOsto, R.M. Harrison, E. Charpantidou, G. Loupa, S. Rapsomanikis, Sci. Total Environ. 384 (2007) 120–133. [44] I.-K. Lee, M. Winterer, Rev. Sci. Instrum. 76 (2005) 095104. [45] P.T. Steele, G.R. Farquar, A.N. Martin, K.R. Coffee, V.J. Riot, S.I. Martin, D.P. Fergenson, E.E. Gard, M. Frank, Anal. Chem. 80 (2008) 4583–4589. [46] S. Geddes, B. Nichols, K. Todd, J. Zahardis, G.A. Petrucci, Atmos. Meas. Tech. 3 (2010) 1175–1183. [47] D.P. Fergenson, M.E. Pitesky, H.J. Tobias, P.T. Steele, G.A. Czerwieniec, S.C. Russell, C.B. Lebrilla, J.M. Horn, K.R. Coffee, A. Srivastava, S.P. Pillai, M.-T.P. Shih, H.L. Hall, A.J. Ramponi, J.T. Chang, R.G. Langlois, P.L. Estacio, R.T. Hadley, M. Frank, E.E. Gard, Anal. Chem. 76 (2004) 373–378. [48] M. Bente, M. Sklorz, T. Streibel, R. Zimmermann, Anal. Chem. 80 (2008) 8991–9004. [49] W.A. Harris, P.T.A. Reilly, W.B. Whitten, Anal. Chem. 79 (2007) 2354–2358. [50] T. Hohaus, D. Trimborn, A. Kiendler-Scharr, I. Gensch, W. Laumer, B. Kammer, S. Andres, H. Boudries, K.A. Smith, D.R. Worsnop, J.T. Jayne, Atmos. Meas. Tech. 3 (2010) 1423–1436. [51] H. Junninen, M. Ehn, T. Peta¨ja¨, L. Luosuja¨rvi, T. Kotiaho, R. Kostiainen, U. Rohner, M. Gonin, K. Fuhrer, M. Kulmala, D.R. Worsnop, Atmos. Meas. Tech. 3 (2010) 1039–1053. [52] M. Ehn, H. Junninen, T. Peta¨ja¨, T. Kurte´n, V.-M. Kerminen, S. Schobesberger, H.E. Manninen, I.K. Ortega, H. Vehkama¨ki, M. Kulmala, D.R. Worsnop, Atmos. Chem. Phys. 10 (2010) 8513– 8530. [53] S.M. Toner, L.G. Shields, D.A. Sodeman, K.A. Prather, Atmos. Environ. 42 (2008) 568–581.