Optimization of protocol for analysis of dicarboxylic acids (DCAs) in ambient aerosol samples using GC-MS Pratibha Vishwakarma, Poonam Nigam, Tarun Gupta Department of Civil Engineering, APTL, India Climate change is a serious global threat and increasing levels of hygroscopic aerosols are one of the major causes behind irregular rainfall and changed radiative forcing. Dicarboxylic acids, which are known for their deliquescence and hygroscopic nature, can act as cloud condensation nuclei (CCN) and ice nuclei (IN), due to which rainfall patterns can be disturbed. Apart from this, DCA analysis in ambient aerosol samples is also gaining interest due to their ability to act as potential organic molecular markers for various anthropogenic and biogenic sources. Even though, low molecular weight DCAs form a group of most frequently analyzed water-soluble organic compounds (WSOCs) present in aerosols, very few studies deal with the optimization of the protocol for qualitative and quantitative analysis of DCAs using Gas Chromatography-Mass Spectrometry (GC-MS). In the present study, we have optimized the extraction of DCAs from aerosol samples collected on quartz filter, by employing several organic solvents with differing relative polarities. Extraction efficiencies of organic solvents were evaluated at different temperatures and pressures using advanced energized dispersive extractor (EDGE, CEM corporation, USA). The high polarity and low levels (approximately 1 ng m −3 ) of dicarboxylic acids demand a derivatization step prior to GC analysis to reduce the polarity of the compounds. BSTFA (N, O-bis-(trimethylsilyl) trifluoroacetamide) + TMCS (trimethylchlorosilane) was chosen as the derivatizing reagent and reaction conditions (temperature, amount of BSTFA, conc. of TMCS) were optimized to give maximum conversions. Separation of compounds was done onHP-5 column with Helium as the carrier gas. Protocol was finalized by selecting the operating parameters of GC-MS in selected Ion monitoring (SIM) mode that reduce thetotalrun time while still maintaininggood resolution of peaks. References 1. Kawamura, K. and Bikkina, S., 2016. A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation. Atmospheric Research, 170, pp.140-160. (doi:https://doi.org/10.1016/j. atmosres.2015.11.018) 2. Sorathia, F., Rajput, P. and Gupta, T., 2018. Dicarboxylic acids and levoglucosan in aerosols from Indo-Gangetic Plain: Inferences from day night variability during wintertime. Science of the total environment, 624, pp.451-460. (doi:https://doi. org/10.1016/j.scitotenv.2017.12.124)
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