On-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry for the analysis of organic acids

An on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry (SFE-LC-GC-MS) system was constructed and applied for the quantitative analysis of selected organic acids. In SFE th e analytes were derivatized in situ with pentafluorobenzyl bromide in the p resence of the modifiers triethylamine and acetone to make them less polar, more volatile, and soluble in supercritical CO2. Parameters that affect de rivatization and extraction were studied. Excess reagent was efficiently re moved by LC prior to GC analysis. Pentane containing 3% ethyl acetate was s uitable for elution of both the SFE solid phase trap and LC-GC. A LC fracti on of 1600 muL could be transferred using an on-column interface and partia lly concurrent solvent evaporation. The whole analysis took place for 2 h i n a closed system. The method was linear in the range 5-200 ng, with detect ion limits around 3 ng. The relative standard deviations of the method were 5-20%. The on-line SFE-LC-GC-MS system was applied for the analysis of aer osol samples collected with Teflon filters in Helsinki, Finland. Benzoic ac id and butyric acid were identified at the level of nanograms per cubic met er, but pinonic acid was not observed. The importance of anthropogenic emis sions for aerosol formation in the region is implied. (C) 2001 John Wiley & Sons, Inc.