Determination of amino acid enantiomers in soils

Determination of amino acid enantiomers in environmental samples is difficu lt, because metals and organic impurities interfere with the analyses. We d eveloped a new gas chromatographic method to assess amino acid enantiomer c oncentrations in complex soil matrices following hot HCl hydrolysis (6 M, 1 2 h, 105 degreesC). The crucial focus was the establishment of a simple, re liable sample clean-up procedure. The presented method involved the adsorpt ion of the enantiomers on a Dowex 50 W X8 cation exchange resin and the rem oval of interfering compounds with 0.1 M oxalic acid prior to amino acid el ution with 2.5 M NH4OH. After conversion to N-pentafluoropropionyl-amino ac id iso-propyl esters, the diastereomers were separated by a Chirasil L-Val capillary column acid quantified by a dame ionization or mass selective det ector. The lower limit of quantification tested here was less than or equal to1 pg injection amount. The recovery of amino acid enantiomers averaged 9 9 +/- 11% for pure standards and 97 +/- 11% for spiked soil hydrolysates. T he general applicability of the method was demonstrated by determination of amino acid enantiomers in taxonomically different soils from different geo graphic regions. The coefficients of variation presented by D/L ratios were 12% for alanine and <10% for the other amino acids. <(c)> 2001 Elsevier Sc ience Ltd. All rights reserved.