Optimization of protocol for analysis of dicarboxylic acids in ambient aerosol samples using GC-MS: method comparison and application

Abstract

Dicarboxylic acids (DCAs), with their deliquescence and hygroscopic nature, can function as cloud condensation nuclei (CCN) and ice nuclei (IN), affecting rainfall patterns. DCA analysis can serve as organic molecular markers for anthropogenic and biogenic sources. 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 this study, we have optimized the extraction of DCAs from aerosol samples by employing several organic solvents with differing relative polarities. Extraction efficiencies of organic solvents were evaluated at different temperatures and pressures using the advanced energized dispersive extractor. The optimized outcomes demonstrate that extraction using methanol at 105 °C for 5 min resulted in high efficiencies, achieving over 80% recovery for all targeted C3-C10 dicarboxylic acids (DCAs). N,O-bis-(trimethylsilyl) trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS) was chosen as the derivatizing reagent, and reaction conditions were optimized to give maximum conversions. The derivatization process, conducted with 30 µL of BSTFA + 1% TMCS in a 200 µL reaction mixture at 70 °C for 90 min, yielded effective and reliable results for subsequent analysis. Separation of compounds was done on the HP-5 column with Helium as the carrier gas. Protocol was finalized by selecting the operating parameters in SIM mode that reduce the total run time while maintaining a clear resolution of peaks.

Keywords: Dicarboxylic acid (DCA); Gas chromatography-mass spectrometry (GC–MS); N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA); Water soluble organic compounds (WSOCs).