Comparison of Gas-liquid and High-performance Liquid Chromatography, and Mass Spectrometry, for the Detection of Organic Acids in Culture Media of Azospirillum brasilense and Desulfovibrio desulfuricans

Abstract

Gas-liquid chromatography (GLC) and high-performance liquid chromatography (HPLC) were used to separate organic acids in spent culture media. Organic acid components were identified on the basis of their retention times and confirmed by gas chromatography/mass spectrometry (GLC/MS). The sensitivity of the analytical procedures varied considerably with each organic acid. GLC analysis of spent culture media esterified by the H2SO,4/methanol procedure failed to detect fumarate, malate and lactate. The BF3/methanol derivatization was particularly sensitive to pyruvate and lactate. GLC/MS, using the BF3/methanol technique, was insensitive to acetate. Cation-exchange HPLC, using a Bio-Rad acid analysis column, did not require prior derivatization of the sample, and proved to be a rapid and non-destructive assay technique for organic acids. This procedure was used to analyse the spent culture media of aerobically grown Azospirillum brasilense and those of Desulfovibrio desulfuricans grown on pyruvate fermentatively or with sulphate as the electron acceptor. Organic acid profiles of the spent culture media obtained by cation-exchange HPLC analysis were compared with those obtained by GLC analysis using both the H2SO4/methanol and the BF3/methanol esterification procedures.