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 the analytes were derivatized in situ with pentafluorobenzyl bromide in the presence of the modifiers triethylamine and acetone to make them less polar, more volatile, and soluble in supercritical CO₂. Parameters that affect derivatization and extraction were studied. Excess reagent was efficiently removed by LC prior to GC analysis. Pentane containing 3% ethyl acetate was suitable for elution of both the SFE solid phase trap and LC-GC. A LC fraction of 1600 μL could be transferred using an on-column interface and partially concurrent solvent evaporation. The whole analysis took place for 2 h in a closed system. The method was linear in the range 5–200 ng, with detection 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 aerosol samples collected with Teflon filters in Helsinki, Finland. Benzoic acid and butyric acid were identified at the level of nanograms per cubic meter, but pinonic acid was not observed. The importance of anthropogenic emissions for aerosol formation in the region is implied. © 2001 John Wiley & Sons, Inc. J Micro Sep 13: 202–210, 2001