Molecular characterisation of ambient aerosols by sequential solvent extractions and high-resolution mass spectrometry

Abstract

Environmental contextOrganic compounds generally make a large contribution to ambient aerosol fine particles, and can influence atmospheric chemistry. Solvent extraction before mass spectrometry is widely used for the determination of organic compounds in aerosols, but the molecular selectivity of different solvents is unclear. We extracted an aerosol sample with various solvents and show how the organic compound profile obtained by mass spectrometry changes depending on the extracting solvent. AbstractFor a comprehensive characterisation of organic compounds in aerosols, samples collected on a hazy day from Beijing were sequentially extracted with various solvents and analysed by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Electrospray ionisation (ESI) was used for the MS analysis. Aerosol samples were extracted in an apolar-to-polar solvent order of n-hexane (n-C6), dichloromethane (DCM), acetonitrile (ACN) and water, and also extracted in reverse sequence. The separated fractions were defined as non-polar, low-polarity, mid-polarity and high-polarity organic compounds respectively. Approximately 70 % of the total organic carbon (TOC) was extractable, of which the water-soluble organic carbon (WSOC) and non-polar organic carbon accounted for 30 and 25 % of the TOC respectively. Non-polar and low-polarity compounds with a high degree of molecular condensation such as oxidised polycyclic aromatic hydrocarbons (PAHs) and nitrogen-containing compounds (CHN) were extracted by n-C6 and DCM. Water-soluble organic matter (WSOM) was predominant with aliphatic and aromatic organosulfates (CHOS) and nitrooxy-organosulfates (CHONS). Most oxygen-containing compounds (CHO) and oxygen- and nitrogen-containing compounds (CHON) with high double-bond equivalents (DBEs) and long carbon chains tended to be extracted into organic solvents.