ANALYSIS FOR SHORT-CHAIN CARBOXYLIC-ACIDS IN FECES BY GAS-CHROMATOGRAPHY WITH AN ION-TRAP DETECTOR

Short-chain carboxylic acids include formic, acetic, propionic, butyric, isobutyric, valeric, isovaleric and caproic acids. The formation of these acies in fecal samples is considered to be representative of bacterial fermentation activity. A recently-published method in which the tert-butyldimethylsilyl derivatives are formed prior to gas chromatography-mass spectrometry, is applied for determination of the acids in fecal samples. An ion-trap detector is used and the conditions for accurate quantitation are described. Calibration plots show linear dynamic ranges of about three orders of magnitude for each acid, e.g., 0.03-30 ng of acetic acid injected, corresponding to 0.26-260 mmol l-1 in the original sample. Recovery studies indicate that results are reproducible within +/- 10% (or +/- 20% for formic acid).