Identification of secondary organic aerosols based on aerosol mass spectrometry

Secondary organic aerosol (SOA) is one of the major components of aerosols in the atmosphere and has not been well understood so far. Due to the complex chemical composition of organic aerosols, the identification of SOA has been a hotspot and difficult issue in the field of aerosol study. This study attempts to quantitatively identify SOA in winter of Shenzhen based on positive matrix factorization (PMF) analysis. Major sources were resolved and SOA was identified subsequently according to the characteristic ion fragments measured by highly time-resolved aerosol mass spectrometer measurement. It showed that in the winter of Shenzhen the average SOA concentration was 9.41 ± 6.33 μg/m³, accounting for 39.9 ± 21.8% of the total organic mass. Compared with primary organic aerosol (POA), the SOA concentrations had no large variation, suggestive of characteristics of regional secondary pollutants. The ratio of SOA/BC had pronounced diurnal variation, similar to that of O _x (O₃+NO₂), indicating SOA formation was significantly controlled by activity of photochemistry in the atmosphere. The most effective period for SOA formation was from 9 am ～3 pm since the SOA/BC ratio increased by 122% during this period. This study provides a new technical method and a new idea for SOA investigation.     

Metal fractionation of atmospheric aerosols via sequential chemical extraction: a review

This review surveys schemes used to sequentially chemically fractionate metals and metalloids present in airborne particulate matter. It focuses mainly on sequential chemical fractionation schemes published over the last 15 years. These schemes have been classified into five main categories: (1) based on Tessiers procedure, (2) based on Chesters procedure, (3) based on Zatkas procedure, (4) based on BCR procedure, and (5) other procedures. The operational characteristics as well as the state of the art in metal fractionation of airborne particulate matter, fly ashes and workroom aerosols, in terms of applications, optimizations and innovations, are also described. Many references to other works in this area are provided.     

基于气溶胶质谱的二次有机气溶胶识别

二次有机气溶胶(SOA)是大气气溶胶十分重要的组成部分,也是目前人们认识最为薄弱的气溶胶组分.由于有机气溶胶化学组成的复杂性,对SOA进行有效的识别和估算一直是国际气溶胶研究领域的热点和难点问题.本研究尝试使用一种新方法来定量识别深圳冬季大气中的SOA:利用气溶胶质谱仪在线观测的高时间分辨率优势和质谱中的特征碎片离子,应用正定矩阵因子解析(PMF)模型对细粒子组分的主要来源进行解析,识别出其中的二次有机物.结果表明:深圳冬季大气细粒子中SOA浓度平均为9.41±6.33μg/m3,占总有机物质量的39.9±21.8%;相比于一次有机气溶胶(POA),SOA浓度水平变化较为平缓,体现了区域性二次污染物的特征.SOA/BC比值具有鲜明的日变化规律,且与Ox(O3+NO2)的日变化规律相似,说明SOA的生成过程显著地受控于大气光化学活性.深圳冬季大气SOA生成最活跃的时段约为9～15时,期间SOA/BC比值增长了122%.本文为研究我国大气二次有机气溶胶提供了一种新的技术方法和思路.     

Determination of polar organic compounds in atmospheric aerosols by gas chromatography with ion trap tandem mass spectrometry

A gas chromatography with ion trap mass spectrometry method has been developed and validated for the analysis of 27 polar organic compounds in atmospheric aerosols. The target analytes were low‐molecular‐weight carboxylic acids and methoxyphenols, as relevant markers of source emissions and photochemical processes of organic aerosols. The operative parameters were optimized in order to achieve the best sensitivity and selectivity for the analysis. In comparison with the previous gas chromatography with mass spectrometry procedure based on single ion monitoring detection, the tandem mass spectrometry technique increased the analytical sensitivity by reducing detection limits for standard solutions from 1–2.6 to 0.1–0.4 ng/μL ranges (concentrations in the injected solution). In addition, it enhanced selectivity by reducing matrix interferences and chemical noise in the chromatogram. The applicability of the developed method in air quality monitoring campaigns was effectively checked by analyzing environmental samples collected in the Po Valley (Northern Italy) in different seasons. The obtained results indicate that the ion trap mass spectrometer may be an ideal alternative to high‐resolution mass spectrometers for the user‐friendly and cost‐effective determination of a wide range of molecular tracers in airborne particulate matter.     

Comprehensive two-dimensional liquid chromatography-time-of-flight mass spectrometry in the analysis of acidic compounds in atmospheric aerosols

A novel method utilising comprehensive two-dimensional liquid chromatography interfaced to electrospray ionisation time-of-flight mass spectrometry was developed for the determination of organic acids in atmospheric aerosols. The system was applied to the analysis of methanolic extracts of filters from a high volume sampler. The enhanced separation power of two-dimensional separation was demonstrated in the analysis of both rural and urban samples. Quantification was performed for compounds for which standards were available. Limit of detection was 2-200ng/ml. Average reproducibility of retention times in each dimensions was 0.1%, and average reproducibility of peak areas was 8% (10mug/ml, n=3).     

Speciation analysis in on-line aerosol mass spectrometry

Ambient aerosol particles affect both the earth's climate and human health. Both effects depend on the chemical composition of the particles including the binding state of specific elements. Modern on-line aerosol mass spectrometry is capable of measuring aerosol composition with high temporal resolution, avoiding artifacts often introduced by classical off-line methods. The two most common types of on-line aerosol mass spectrometers, laser desorption/ionization mass spectrometers (LDI-MS) and thermal desorption electron impact ionization mass spectrometers (TD-EI-MS) provide reliable information on the most common ambient inorganic and organic aerosol species with high temporal resolution. However, for less common aerosol species identification with both types of instrument is frequently associated with large uncertainties. Here, we provide an overview of the element speciation capabilities of current on-line aerosol mass spectrometry for both carbonaceous and non-carbon-containing aerosol species. We describe limitations and other issues for this type of on-line aerosol analysis.     

Detection and quantification of levoglucosan in atmospheric aerosols: a review

Levoglucosan is a tracer for biomass burning sources in atmospheric aerosol particles. Therefore, much effort has been recently put into developing methods for its quantification. This review describes and compares both established and emerging analytical methods for levoglucosan quantification in ambient aerosol samples, with the special needs of the environmental analytical chemist in mind.     

Molecular chemistry of organic aerosols through the application of high resolution mass spectrometry

Understanding the molecular composition and fundamental chemical transformations of organic aerosols (OA) during their formation and aging is both a major challenge and the area of great uncertainty in atmospheric research. Particularly, little is known about fundamental relationship between the chemical composition and physicochemical properties of OA, their atmospheric history, evolution, and the impact on the environment. Ambient soft-ionization methods combined with high-resolution mass spectrometry (HR-MS) analysis provide detailed information on the molecular content of OA that is pivotal for improving the understanding of their complex composition, multi-phase aging chemistry, direct (light absorption and scattering) and indirect (aerosol-cloud interactions) effects on atmospheric radiation and climate, health effects. The HR-MS methods can detect thousands of individual OA constituents at once, provide their elemental formulae from accurate mass measurements and structural information based on tandem mass spectrometry. Integration with additional analytical tools, such as chromatography and UV/Vis absorption spectroscopy, makes it possible to further separate OA compounds by their polarity and ability to absorb solar radiation. The goal of this perspective is to describe contemporary HR-MS methods, review recent applications in field and laboratory studies of OA, and explain how the information obtained from HR-MS methods can be translated into an improved understanding of OA chemistry.     

Liquid chromatography/negative ion atmospheric pressure photoionization mass spectrometry: a highly sensitive method for the analysis of organic explosives

Gas chromatography/mass spectrometry (GC/MS) is applied to the analysis of volatile and thermally stable compounds, while liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI‐MS) and liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) are preferred for the analysis of compounds with solution acid‐base chemistry. Because organic explosives are compounds with low polarity and some of them are thermally labile, they have not been very well analyzed by GC/MS, LC/APCI‐MS and LC/ESI‐MS. Herein, we demonstrate liquid chromatography/negative ion atmospheric pressure photoionization mass spectrometry (LC/NI‐APPI‐MS) as a novel and highly sensitive method for their analysis. Using LC/NI‐APPI‐MS, limits of quantification (LOQs) of nitroaromatics and nitramines down to the middle pg range have been achieved in full MS scan mode, which are approximately one order to two orders magnitude lower than those previously reported using GC/MS or LC/APCI‐MS. The calibration dynamic ranges achieved by LC/NI‐APPI‐MS are also wider than those using GC/MS and LC/APCI‐MS. The reproducibility of LC/NI‐APPI‐MS is also very reliable, with the intraday and interday variabilities by coefficient of variation (CV) of 0.2–3.4% and 0.6–1.9% for 2,4,6‐trinitrotoluene (2,4,6‐TNT). Copyright © 2008 John Wiley & Sons, Ltd.     

Sampling and analysis of individual particles by aerosol mass spectrometry

Over the past decade, aerosol mass spectrometry has developed into a powerful method for characterizing individual particles in air. Recent advances in the design of inlets and mass spectrometers have extended the size range of particles that can be analyzed. In this tutorial, fundamental aspects of particle motion in sampling inlets are introduced. Basic experimental configurations for achieving a high analysis rate and the ability of laser ablation to provide chemical composition information are reviewed. An example of the use of this technology to study atmospheric phenomena is also presented. Significant opportunity exists for designing new experiments at the interface of aerosol mass spectrometry and conventional molecular mass spectrometry.     

Characterization of carboxylic acids in atmospheric aerosols using hydrophilic interaction liquid chromatography tandem mass spectrometry

A sensitive hydrophilic interaction liquid chromatography/electrospray ionization mass spectrometry (HILIC/ESI-MS/MS) method was developed for determination of selected aliphatic (i.e. malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, maleic, fumaric, glycolic and pyruvic acid), alicyclic (i.e. cis-pinonic and pinic acid) and aromatic (i.e. trimesic, phthalic acid and its isomers) carboxylic acids. Analytes were separated on an amide column using a gradient elution with a 10mM constant ionic strength mobile phase containing acetonitrile and aqueous ammonium acetate buffer (pH 5.0). The influence of the buffer type, pH, polar modifier and temperature on analyte retention under HILIC was studied. Static sonication-assisted solvent extraction was optimized for sample preparation prior to analysis. The recoveries obtained were higher than 90% for most analytes. The method was proven to be sensitive with limits of detection ranged from 0.03 to 16.0 μg/L in selected reaction monitoring mode (SRM). The repeatability and intermediate precision of the method, expressed as RSD (%) of the peak area ratio between analytes and their internal standards were generally lower than 5%. The method was successfully applied for determination of the studied acids in samples of ambient aerosol particles. A big advantage of the new method is also its ability to detect and separate the isobaric compounds of the selected carboxylic acids. Our results demonstrate that the method is specific and sensitive for the determination of a wider range of polar carboxylic acids at low concentrations in complex samples of aerosol particles.     

Comparison of laser microprobe mass spectrometry and fast-atom-bombardment mass spectrometry for organic analysis

Both the techniques mentioned provide molecular weight and structural information, but laser microprobe mass spectrometry (LMMS) also provides greater control over the degree of fragmentation and enhanced sensitivity. In addition, LMMS allows microprobe analysis (i.e., spatial resolution of a few μm²) as well as providing quantitative measurements. The less energetic nature of fast-atom-bombardment mass spectrometry (FAB-MS) makes it more suitable for the analysis of highly labile polar compounds and high-mass biopolymers.     

A critical review of advanced analytical techniques for water-soluble organic matter from atmospheric aerosols

Water-soluble organic matter (WSOM) from air particles plays a potentially important role in the climate system, yet little is known about its molecular composition and physico-chemical properties. During the past decade, the rapidly-evolving field of analytical instrumentation has produced sophisticated tools capable of providing molecular level information on this organic-aerosol fraction.This article presents a critical review of the major applications of these advanced analytical methods in WSOM analysis. We emphasize off-line methods relying on nuclear magnetic resonance and infrared spectroscopies, and high-resolution mass spectrometry. We also discuss the most prominent analytical methods for near real-time measurements of particulate WSOM. We address the limitations of advanced off-line and on-line instrumental techniques, and, finally, outline the major challenges ahead to improve the current knowledge on the chemical structures of aerosol WSOM.     

Direct analysis of volatile organic compounds in foods by headspace extraction atmospheric pressure chemical ionisation mass spectrometry

Rationale

The rapid screening of volatile organic compounds (VOCs) by direct analysis has potential applications in the areas of food and flavour science. Currently, the technique of choice for VOC analysis is gas chromatography/mass spectrometry (GC/MS). However, the long chromatographic run times and elaborate sample preparation associated with this technique have led a movement towards direct analysis techniques, such as selected ion flow tube mass spectrometry (SIFT‐MS), proton transfer reaction mass spectrometry (PTR‐MS) and electronic noses. The work presented here describes the design and construction of a Venturi jet‐pump‐based modification for a compact mass spectrometer which enables the direct introduction of volatiles for qualitative and quantitative analysis.

Methods

Volatile organic compounds were extracted from the headspace of heated vials into the atmospheric pressure chemical ionization source of a quadrupole mass spectrometer using a Venturi pump. Samples were analysed directly with no prior sample preparation. Principal component analysis (PCA) was used to differentiate between different classes of samples.

Results

The interface is shown to be able to routinely detect problem analytes such as fatty acids and biogenic amines without the requirement of a derivatisation step, and is shown to be able to discriminate between four different varieties of cheese with good intra and inter‐day reproducibility using an unsupervised PCA model. Quantitative analysis is demonstrated using indole standards with limits of detection and quantification of 0.395 μg/mL and 1.316 μg/mL, respectively.

Conclusions

The described methodology can routinely detect highly reactive analytes such as volatile fatty acids and diamines without the need for a derivatisation step or lengthy chromatographic separations. The capability of the system was demonstrated by discriminating between different varieties of cheese and monitoring the spoilage of meats.     

Determination of oxygenated polycyclic aromatic hydrocarbons in atmospheric aerosol samples by liquid chromatography-tandem mass spectrometry

In this paper, the development of an analytical method using liquid chromatography-tandem mass spectrometry (LC-MS-MS) with atmospheric pressure chemical ionization (APCI) for the determination of 17 oxygenated polycyclic aromatic hydrocarbons (OPAH) is described. These OPAH include ketones, pyrones and diketones. The APCI interface parameters have been optimized for maximum sensitivity. Positive ion mode was proved to be most sensitive for ketones and pyrones while negative ion mode gave better detection limits for target diketones. The detection limits of the method ranged from less than 1.20microg L(-1) for several OPAH solutions (between 0.10 and 0.70microg L(-1) for positive mode and between of 0.19 and 1.20microg L(-1) for negative mode). The analytical method was applied particulate matter (PM(2.5)) samples collected over 24-48h periods between March 2005 and June 2005 in Tempe (Arizona, USA). Before analysis aerosol samples were solvent extracted and concentrated to a final volume of 1mL of methanol. OPAH concentrations observed for this urban site ranged from 0.22 to 3.60ngm(-3).     

Coupling two-step laser desorption/ionization with aerosol time-of-flight mass spectrometry for the analysis of individual organic particles

Analysis of organic compounds in aerosol particles using real-time single particle techniques is difficult because of extensive fragmentation that occurs in the laser desorption/ionization step. In an effort to avoid such fragmentation processes, we coupled a “soft” two-step laser desorption/ionization technique (L2MS) with aerosol time-of-flight mass spectrometry (ATOFMS). In these studies, we find this combination preserves intact organic molecules while providing the real-time mass spectra of suspended aerosol particles. Mass spectra of particles analyzed by one-step desorption mass spectrometry and L2MS are presented for comparison. These include 2,4-dihydroxybenzoic acid as a test case and wood and cigarette combustion particles as real world examples. This is the first published demonstration of L2MS performed on single particles not deposited on a substrate prior to analysis.     

Direct analysis of highly oxidised organic aerosol constituents by on-line ion trap mass spectrometry in the negative-ion mode

On-line ion trap mass spectrometry (ITMS) enables the characterisation of constituents of biogenic secondary organic aerosols in complex organic reaction mixtures. This real-time analysis is achieved by directly introducing the airborne particles into the ion source of the mass spectrometer. Negative-ion chemical ionisation at atmospheric pressure (APCI(-)) was used as the ionisation method of choice. The aerosols were generated from the gas-phase ozonolysis of two C10H16-terpenes (alpha-pinene and limonene), and investigated by performing on-line APCI(-)-ITMS(n). Highly oxidised compounds were tentatively identified as important particle-phase products. Based on recent investigations of low-energy collision-induced dissociation pathways of a wide range of deprotonated multifunctional carboxylic acid species derived from monoterpene precursors (Warscheid B, Hoffmann T. Rapid Commun. Mass Spectrom. 2001; 15: 2259), the formation of structurally different C10H16O5 and C10H16O6 species, such as acidic esters from alpha-pinene and aldo-hydroxycarboxylic acids from limonene, is proposed.