GC–MS analysis of water-soluble organics in atmospheric aerosol: Response surface methodology for optimizing silyl-derivatization for simultaneous analysis of carboxylic acids and sugars

Saccharides in atmospheric particulate and sedimentary organic matter: Status overview and future perspectives

Saccharides are omnipresent compounds in terrestrial and marine ecosystems. Since the 2000s, their role in environmental and geochemical studies has significantly increased, but only anhydrosaccharides (mainly levoglucosan) have been reviewed. Here we present the wider knowledge about saccharides in organic matter of aerosols, bottom sediments, soils, dust, and sedimentary rocks. The main purpose here is to characterize the possible sources of saccharides, as well as sacharol formation, seasonal variability, and the possible applications in environmental and paleoenvironmental interpretations. Different saccharide sources were designated, including biomass burning, and particulate matter such as pollen, spores, lichen, and fungi, as well as polysaccharide decomposition as possible inputs of monosaccharides. The main focus was on the most common saccharides encountered in environmental samples and sedimentary rocks. These are the mono- and disaccharides glucose, fructose, sucrose, and trehalose, and sacharols arabitol and mannitol. The anhydrosaccharides levoglucosan, mannosan, and galactosan were evaluated as ancient wildfire indicators and industrialization tracers found in lacustrine sediments starting from Pleistocene to contemporary deposits. However, other anhydrosaccharides like xylosan and arabinosan were also found as products of fossil wood burning. These anhydrosaccharides have the potential to be further tracers of hemicellulose burning. Additional recommendations are proposed for future research, including environmental and paleoenvironmental topics that need to be addressed.

Molecular Markers in Ambient Air Associated with Biomass Burning in Morelos, México

Atmospheric particles with an aerodynamic diameter less than or equal to 2.5 micrometers (PM2.5) were collected at two sites located in the urban area of the city of Cuernavaca (Morelos) during a season when a large number of forest fires occurred. Three dicarboxylic acids (malonic, glutaric and succinic) and levoglucosan were analyzed by liquid chromatography coupled with mass spectrometry (ESI-Q-TOF) and soluble potassium (K+) was analyzed by ion chromatography. The concentration of PM2.5 increased on the days when the highest number of forest fires occurred. A strong correlation was observed between levoglucosan and K+, confirming the hypothesis that both are tracers of biomass burning (r = 0.57, p < 0.05). Levoglucosan (average 367.6 ng m−3, Site 2) was the most abundant compound, followed by succinic acid (average 101.7 ng m−3, Site 2), glutaric acid (average 63.2 ng m−3, Site 2), and malonic acid (average 46.9 ng m−3, Site 2), respectively. The ratio of C3/C4 concentrations ranged from 0.5 to 1.2, with an average of 0.8, which suggests great photochemical activity in the Cuernavaca atmosphere. The ratio of K+/levoglucosan concentrations (0.44) indicates that open fires are the main source of these tracers. The positive correlations between PM2.5 and levoglucosan and succinic and malonic acids suggest that such compounds are contributing to secondary organic aerosol particle formation.

Aromatic acids as biomass-burning tracers in atmospheric aerosols and ice cores: A review

Biomass burning (BB) is one of the largest sources of carbonaceous aerosols with adverse impacts on air quality, visibility, health and climate. BB emits a few specific aromatic acids (p-hydroxybenzoic, vanillic, syringic and dehydroabietic acids) which have been widely used as key indicators for source identification of BB-derived carbonaceous aerosols in various environmental matrices. In addition, measurement of p-hydroxybenzoic and vanillic acids in snow and ice cores have revealed the historical records of the fire emissions. Despite their uniqueness and importance as tracers, our current understanding of analytical methods, concentrations, diagnostic ratios and degradation processes are rather limited and scattered in literature. In this review paper, firstly we have summarized the most established methods and protocols for the measurement of these aromatic acids in aerosols and ice cores. Secondly, we have highlighted the geographical variability in the abundances of these acids, their diagnostic ratios and degradation processes in the environments. The review of the existing data indicates that the concentrations of aromatic acids in aerosols vary greatly with locations worldwide, typically more abundant in urban atmosphere where biomass fuels are commonly used for residential heating and/or cooking purposes. In contrast, their concentrations are lowest in the polar regions which are avoid of localized emissions and largely influenced by long-range transport. The diagnostic ratios among aromatic acids can be used as good indicators for the relative amounts and types of biomass (e.g. hardwood, softwood and herbaceous plants) as well as photochemical oxidation processes. Although studies suggest that the degradation processes of the aromatic acids may be controlled by light, pH and hygroscopicity, a more careful investigation, including closed chamber studies, is highly appreciated.

An optimized two-step derivatization method for analyzing diethylene glycol ozonation products using gas chromatography and mass spectrometry

The ozonation of hydroxyl compounds (e.g., sugars and alcohols) gives a broad range of products such as alcohols, aldehydes, ketones, and carboxylic acids. This study developed and optimized a two-step derivatization procedure for analyzing polar products of aldehydes and carboxylic acids from the ozonation of diethylene glycol (DEG) in a non-aqueous environment using gas chromatography-mass spectrometry. Experiments based on Central Composite Design with response surface methodology were carried out to evaluate the effects of derivatization variables and their interactions on the analysis. The most desirable derivatization conditions were reported, i.e., oximation was performed at room temperature overnight with the o-(2,3,4,5,6-pentafluorobenzyl) hydroxyl amine to analyte molar ratio of 6, silylation reaction temperature of 70°C, reaction duration of 70min, and N,O-bis(trimethylsilyl)-trifluoroacetamide volume of 12.5μL. The applicability of this optimized procedure was verified by analyzing DEG ozonation products in an ultrafine condensation particle counter simulation system.

Optimizing Mass Spectrometry Analyses: A Tailored Review on the Utility of Design of Experiments

Mass spectrometry (MS) has emerged as a tool that can analyze nearly all classes of molecules, with its scope rapidly expanding in the areas of post-translational modifications, MS instrumentation, and many others. Yet integration of novel analyte preparatory and purification methods with existing or novel mass spectrometers can introduce new challenges for MS sensitivity. The mechanisms that govern detection by MS are particularly complex and interdependent, including ionization efficiency, ion suppression, and transmission. Performance of both off-line and MS methods can be optimized separately or, when appropriate, simultaneously through statistical designs, broadly referred to as "design of experiments" (DOE). The following review provides a tutorial-like guide into the selection of DOE for MS experiments, the practices for modeling and optimization of response variables, and the available software tools that support DOE implementation in any laboratory. This review comes 3 years after the latest DOE review (Hibbert DB, 2012), which provided a comprehensive overview on the types of designs available and their statistical construction. Since that time, new classes of DOE, such as the definitive screening design, have emerged and new calls have been made for mass spectrometrists to adopt the practice. Rather than exhaustively cover all possible designs, we have highlighted the three most practical DOE classes available to mass spectrometrists. This review further differentiates itself by providing expert recommendations for experimental setup and defining DOE entirely in the context of three case-studies that highlight the utility of different designs to achieve different goals. A step-by-step tutorial is also provided.

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.

Alkylsilyl derivatives for gas chromatography

Alkylsilyl reagents are the most widely used reagents for the derivatization of polar compounds containing labile hydrogen atoms for gas chromatography. In this article the reagents and reaction conditions for the formation of trimethylsilyl, alkyldimethylsilyl (particularly t-butyldimethylsilyl), cyclic siliconides, haloalkyldimethylsilyl, and flophemesyl (pentafluorophenyldimethylsilyl) derivatives for a wide range of functional groups are reviewed. The importance of steric hindrance on reaction rates and completion, choice of reaction conditions, stability of derivatives, and options for selective detection are described.