Low Molecular Weight Monocarboxylic Acids Research Articles

Enhanced levels of atmospheric low-molecular weight monocarboxylic acids in gas and particulates over Mt. Tai, North China, during field burning of agricultural wastes

To understand the source and atmospheric behaviour of low molecular weight monocarboxylic acids (monoacids), gaseous (G) and particulate (P) organic acids were collected at the summit of Mt. Tai in the North China Plain (NCP) during field burning of agricultural waste (wheat straw). Particulate organic acids were collected with neutral quartz filter whereas gaseous organic acids were collected with KOH-impregnated quartz filter. Normal (C1-C10), branched (iC4-iC6), hydroxy (lactic and glycolic), and aromatic (benzoic) monoacids were determined with a capillary gas chromatography employing p-bromophenacyl esters. We found acetic acid as the most abundant gas-phase species whereas formic acid is the dominant particle-phase species. Concentrations of formic (G/P 1 570/1 410 ng m−3) and acetic (3 960/1 120 ng m−3) acids significantly increased during the enhanced field burning of agricultural wastes. Concentrations of formic and acetic acids in daytime were found to increase in both G and P phases with those of K+, a field-burning tracer (r = 0.32–0.64). Primary emission and secondary formation of acetic acid is linked with field burning of agricultural wastes. In addition, we found that particle-phase fractions (Fp = P/(G + P)) of formic (0.50) and acetic (0.31) acids are significantly high, indicating that semi-volatile organic acids largely exist as particles. Field burning of agricultural wastes may play an important role in the formation of particulate monoacids in the NCP. High levels (917 ng m−3) of particle-phase lactic acid, which is characteristic of microorganisms, suggest that microbial activity associated with terrestrial ecosystem significantly contributes to the formation of organic aerosols.

Homologous series of low molecular weight (C1-C10) monocarboxylic acids, benzoic acid and hydroxyacids in fine-mode (PM2.5) aerosols over the Bay of Bengal: Influence of heterogeneity in air masses and formation pathways

Low molecular weight monocarboxylic acids (LMW monoacids) are most abundant volatile organic compounds (VOCs) in the atmosphere and often act as important contributors to the acidity of precipitation in addition to inorganic acids. However, there is a large uncertainty in the sources and secondary formations of these acids in the atmosphere. This study reports homologous series of LMW monoacids, including normal (C1-C10), branched chain (iC4-iC6), aromatic (benzoic acid) and hydroxyacids (lactic and glycolic acids) in the fine-mode (PM2.5) aerosols collected over the Bay of Bengal (BoB) during a winter cruise (December 2008 to January 2009). The samples were associated with two distinct continental air masses arriving from the Indo-Gangetic Plain (IGP-outflow) and Southeast Asia (SEA-outflow). The molecular distributions of organic acids are characterized by the dominance of formic acid (C1) followed by acetic acid (C2) and nonanoic acid (C9) in the IGP-outflow, whereas dominance of C1 or C9 was observed in the SEA-outflow followed by C2. Formic-to-acetic acid (C1/C2) ratios were higher than unity (mean: 1.3 ± 0.3) in the IGP-outflow, whereas they were less than unity (0.9 ± 0.5) in the SEA-outflow. These results suggest that secondary formation of organic acids is largely important in the IGP-outflow whereas primary emission is a major source of organic acids in the SEA-outflow. Based on the correlation coefficient matrix analysis and C1/C2 and C4/C3 ratios, we consider that the sources of C1 are probably associated with the secondary formation via the oxidation of biogenic VOCs, while C2 has both primary and secondary formations associated with anthropogenic sources in the IGP-outflow. On the other hand, C1 and C2 have similar sources (both primary and secondary) originated from biomass burning and bacterial activities via long-range atmospheric transport in the SEA-outflow, as inferred from the MODIS fire spot data, significant concentrations of isovaleric acid (iC5), and a significant correlation (r = 0.67) between nss-K+ and total LMW monoacids.

Low Molecular Weight Monocarboxylic Acids in PM2.5 and PM10: Quantification, Seasonal Variation and Source Apportionment

ABSTRACTPM2.5 and PM10 aerosols from a semi-urban site of Agra (27°10′N, 78°05′E) in North-Central India were analyzed for carbonaceous aerosols (Organic and Elemental carbon), low molecular weight monocarboxylic acids (Acetic and Formic acid) along with inorganic ions (Cl–, NO3–, SO42–, K+ and Ca2+) during April 2014 to August 2015. The average PM2.5 and PM10 mass concentrations were 86.3 ± 71.3 and 169.7 ± 100.5 µg m–3, respectively; about 45% of PM2.5 and 67% of PM10 samples were above NAAQ (National Ambient Air Quality) standards. The average organic carbon (OC) and elemental carbon (EC) concentrations were 18.2 ± 12.3 and 6.7 ± 4.5 µg m–3, respectively in PM2.5 and 25.2 ± 14.1 and 8.1 ± 5.9 µg m–3 respectively in PM10. The average concentration of acetic acid (AA) in PM2.5 and PM10 were 330 ± 211 and 392 ± 224 ng m–3 respectively. The average concentration of formic acid (FA) in PM2.5 and PM10 were 348 ± 193 and 336 ± 175 ng m–3 respectively. Formic acid concentration was higher in PM2.5 than PM10 but the difference is not statistically significant. Both AA and FA showed similar seasonal variation: winter > post-monsoon > summer > monsoon. Low temperature and high relative humidity in winter season favours gas to particle conversion resulting in high concentrations. The average FA to AA (F/A) ratio was 0.69 indicating dominance of primary sources at the study site. Correlation analysis of AA and FA with major ions (Cl–, NO3–, SO42–, K+ and Ca2+), EC, secondary organic carbon and trace gases (O3 and CO) was performed to identify their primary or secondary origin. The results of correlation analysis suggest that AA is mainly contributed by primary sources while FA originates from secondary sources.

Determination of Impurities in Bioproduced Succinic Acid

At present, significant research resources are directed towards development of renewable products for replacing petrochemicals such as succinic acid. The critical component of this research is the identification of impurities which have a detrimental impact on further processing of succinic acid. We have adapted derivatization with gas chromatography - mass spectrometry to identify and quantify more than 120 impurities in several succinic acid samples. This study focused on petroleum based succinic acid as well as bio-based samples that use a modified E. coli strain for fermentation. To enable an accurate quantification of both the target product and common impurities, we evaluated the acetonitrile extraction efficiency as an alternative to direct derivatization, and then compared several derivatization agents for trimethylsilylation. A prior acetonitrile extraction was shown to be essential to detect impurities in trace concentrations. N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) was most efficient for derivatization of saccharides and low molecular weight monocarboxylic acids. However, the presence of pyridine was necessary for derivatization of saccharides and polyalcohols with BSTFA, whereas low molecular weight acids had to be quantified without pyridine. Fourteen representative bioproduced succinic acid samples differing in production stage, and cultivation method were characterized. The screening of initial process (1st stage of synthesis) samples showed monocarboxylic acids as most abundant and suggested occurrence of saccharides. Thus we have developed method allowing for quantification of carboxylic acids and saccharides with limits of detection between 0.02-0.3 ng. In initial process bacterial samples and also petrochemical sample, formic, acetic, lactic, oxalic, benzoic, citric and malic acids as well as glycerol, butanediol, and glucose were found in a range of 0.02-1160 μg/g. In final processed samples, formic and acetic acid, and glucose were found in concentration lower than 0.001% demonstrating effectiveness of process as well as applicability of the method as quality control of the process.

Scavenging of SO 4− radical anions by mono- and dicarboxylic acids in the Mn(II)-catalyzed S(IV) oxidation in aqueous solution

The rate constants for reactions of the SO 4 − radical anion with some low molecular weight monocarboxylic acids (MCAs) and dicarboxylic acids (DCAs) and their anions using the laser flash photolysis-long path laser absorption (LFP-LPLA) technique were determined. The present study contains the first measured rate constants for SO 4 − reactions with glycolic, lactic, malic and malonic acid. The rate constants are found to be in the range from 10 5 to 10 7 M −1 s −1, with the lower values found for acids and higher values for their respective anions. In addition, the rate constants for scavenging of SO 4 − by all investigated organics in the Mn(II)-catalyzed S(IV) autoxidation at pH 4.5 and T=25 °C were determined by means of the reversed rate method. The comparison between these rate constants and the rate constants obtained by direct measurements confirms the proposed inhibiting mechanism for the Mn(II)-catalyzed S(IV) autoxidation in the presence of monocarboxylic acids. In the case of formic acid, which causes the highest inhibition, this mechanism can explain the second part of kinetic traces (i.e. after the induction period). Surprisingly, although dicarboxylic acids are reactive toward SO 4 − they do not contribute to the inhibition of S(IV) oxidation (especially malic and malonic acids).

Structure and isotopic ratios of aliphatic side chains in the insoluble organic matter of the Murchison carbonaceous chondrite

We report in this paper the first molecular and isotopic characterization of individual aliphatic side chains from the insoluble organic matter (IOM) in the Murchison carbonaceous chondrite using a novel combined approach of RuO 4 oxidation and solid phase microextraction (SPME). The aliphatic side chains in the IOM of Murchison were first released by oxidizing aromatic structures using RuO 4. Because the IOM of carbonaceous chondrites contains predominantly short (C 1 to C 9) aliphatic substitutions, the resulting low molecular weight monocarboxylic acids (MCAs) are highly volatile and water-soluble. The conventional aqueous extraction and derivatization procedures following RuO 4 oxidation are unable to recover MCAs for subsequent analyses. We overcame this problem by employing SPME to directly capture the MCAs from the aqueous solution. We selected a SPME fiber with greater affinity for longer chain monoacids to compensate for the exponential decline of monoacid concentrations with increasing carbon numbers in meteorite IOM, allowing more accurate identification and quantification for the less abundant monoacids. We also determined the carbon and hydrogen isotopic ratios of individual MCAs derived from Murchinson IOM. Our results reveal significant similarity in both molecular structures and hydrogen isotopic ratios between the IOM aliphatic side chains and water-soluble MCAs in Murchison, suggesting that these compounds had common precursors. Our combined new approach of RuO 4 oxidation-SPME provides a new way to probe the molecular and isotopic characteristics of aliphatic side chains in carbonaceous chondrites.

Carbon isotopic composition of acetic acid generated by hydrous pyrolysis of macromolecular organic matter from the Murchison meteorite

Abstract— Low molecular weight monocarboxylic acids, including acetic acid, are some of the most abundant organic compounds in carbonaceous chondrites. So far, the 13C- and D-enriched signature of water-extractable carboxylic acids has implied an interstellar contribution to their origin. However, it also has been proposed that monocarboxylic acids could be formed by aqueous reaction on the meteorite parent body. In this study, we conducted hydrous pyrolysis of macromolecular organic matter purified from the Murchison meteorite (CM2) to examine the generation of monocarboxylic acids with their stable carbon isotope measurement. During hydrous pyrolysis of macromolecular organic matter at 270–330 °C, monocarboxylic acids with carbon numbers ranging from 2 (C2) to 5 (C5) were detected, acetic acid (CH3COOH; C2) being the most abundant. The concentration of the generated acetic acid increased with increasing reaction temperature; up to 0.48 mmol acetic acid/g macromolecular organic matter at 330 °C. This result indicates that the Murchison macromolecule has a potential to generate at least ˜0.4 mg acetic acid/g meteorite, which is about four times higher than the amount of water-extractable acetic acid reported from Murchison. The carbon isotopic composition of acetic acid generated by hydrous pyrolysis of macromolecular organic matter is ˜-27‰ (versus PDB), which is much more depleted in 13C than the water-extractable acetic acid reported from Murchison. Intramolecular carbon isotope distribution shows that methyl (CH3-)-C is more enriched in 13C relative to carboxyl (-COOH)-C, indicating a kinetic process for this formation. Although the experimental condition of this study (i.e., 270–330 °C for 72 h) may not simulate a reaction condition on parent bodies of carbonaceous chondrite, it may be possible to generate monocarboxylic acids at lower temperatures for a longer period of time.

Molecular and compound-specific isotopic characterization of monocarboxylic acids in carbonaceous meteorites

Low molecular weight monocarboxylic acids are the most abundant water soluble organic compounds in the Murchison and many other CM type carbonaceous chondrites. In this study, we examined the monocarboxylic acids in Murchison and EET96029.20 carbonaceous meteorites using a new sample preparation and introduction technique for gas chromatograph recently developed for volatile, water-soluble organic compounds: solid phase micro-extraction (SPME). We identified more than 50 monocarboxylic acids from Murchison compared with the 18 compounds reported previously. Formic acid, a known interstellar molecule, has been fully analyzed in these carbonaceous meteorites, with its δD value suggesting an interstellar origin. We determined both carbon and hydrogen isotopic ratios of individual monocarboxylic acids in Murchison, to better define the origins and genetic relationships of these compounds. The compound-specific isotopic data reveal a large enrichment in 13C (δ 13C up to + 32.5 ‰) and particularly D (δD up to + 2024 ‰). The branched acids are substantially enriched in both 13C and D relative to the straight chain acids, with those branched acids containing a quaternary carbon showing the greatest isotopic enrichment. The isotopic difference may be attributed to variations in the different synthetic regimes or terrestrial input of straight chain acids.

Low molecular weight monocarboxylic acids and .GAMMA.-lactones in Neogene sediments of the Shinjo basin.

Homologous series of low molecular weight monocarboxylic acids (C2 to C12) and γ-lactones (C5 to C12) were detected in Miocene to Pliocene sediments of Shinjo basin. Abundances of the monocarboxylic acids are 10-6 to 10-8g/g, and those of the γ-lactones are 10-7 to 10-9 g/g. The monocarboxylic acids show the unique predominance of nonanoic acid over octanoic and decanoic acids. The γ-lactones show a predominance of hexanoic lactone in most of the sediments. No δ-lactones were detected in the sediments. It seems that the two classes of organic compounds were converted from common precursors, namely cis-9 unsaturated fatty acids, during the early stages of sediment diagenesis.