Derivatization procedures and determination of levoglucosan and related monosaccharide anhydrides in atmospheric aerosols by gas chromatography–mass spectrometry

This study evaluated the derivatization procedures for detecting the three most commonly monosaccharide anhydrides (MAs) (levoglucosan, mannosan and galactosan) in atmospheric aerosols using gas chromatography–mass spectrometry (GC–MS). Various silylating agents, mainly trimethylsilylating agents (TMS), were compared and the effects of various contents of trimethylchlorosilane (TMCS, as a stimulator) were evaluated to optimize the conditions for detecting these compounds in aerosol samples. Differences among the abundances of the derivatives were caused by the sterical hindrance of three hydroxyl groups in the structures of monosaccharide anhydrides. The effects of the reaction time and temperature were also examined. The optimal reaction time and temperature were 60 min and 80 °C with 1% TMCS plus 0.2% 1,4-dithioerythritol (DTE). Under these conditions, the percentages of formation of bis-O-TMS derivatives (as by-products) were 23, 29 and 10% for galactosan, mannosan and levoglucosan, respectively. The concentrations of galactosan, mannosan and levoglucosan in particles of smoke samples ranged from 29 to 88, 23 to 69 and 77 to 380 ng/m3, respectively; and in particles of atmospheric aerosols ranged from 0.06 to 0.75, n.d. to 0.49 and 1.6 to 132 ng/m3, respectively. Levoglucosan was the dominant MAs detected in both type of samples. Less than 10% quantitation difference was obtained when bis-O-TMS derivatives were included in the calculation.