Gas Chromatography-Mass Spectrometry of N- Heptafluorobutyryl Isobutyl Esters of Amino Acids in the Analysis of the Kinetics of [15N]H4+ Assimilation in Lemna minor L

Abstract

Rapid, sensitive and selective methods for the determination of the 15N abundance of amino acids in isotopic tracer experiments with plant tissues are described and discussed. Methodology was directly tested in an analysis of the kinetics of [15N]H4+ assimilation in L. minor L. The techniques utilize gas chromatography-mass spectrometry selected ion monitoring of major fragments containing the N moiety of N-heptafluorobutyryl isobutyl esters of amino acids. The ratio of selected ion pairs at the characteristic retention time of each amino acid derivative can be used to calculate 15N abundance with an accuracy of .+-. 1 atom % excess 15N using samples containing as little as 30 pmol of individual amino acids. Up to 11 individual amino acid derivatives can be selectively monitored in a single chromatogram of 30 min. Apparently, these techniques will be useful in situations where the small quantities of N available for analysis have hindered the use of 15N-labeled precursors.