Gas Chromatography-Mass Spectrometry of N- Heptafluorobutyryl Isobutyl Esters of Amino Acids in the Analysis of the Kinetics of [N]H(4) Assimilation in Lemna minor L.

Rapid, sensitive, and selective methods for the determination of the (15)N abundance of amino acids in isotopic tracer experiments with plant tissues are described and discussed. Methodology has been directly tested in an analysis of the kinetics of [(15)N]H(4) (+) assimilation in Lemna 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 (15)N abundance with an accuracy of +/-1 atom% excess (15)N using samples containing as little as 30 picomoles of individual amino acids. Up to 11 individual amino acid derivatives can be selectively monitored in a single chromatogram of 30 minutes. It is suggested that these techniques will be useful in situations where the small quantities of N available for analysis have hitherto hindered the use of (15)N-labeled precursors.