Determination of the 13C-labeling pattern of glutamate by gas chromatography-mass spectrometry

We present a simple technique for determining the 13C-labeling pattern of glutamate by gas chromatography-mass spectrometry. Glutamate is derivatized with dimethylformamide dimethyl acetal (Methyl-8R). The dimethylaminomethylene methyl ester derivative of glutamate yields fragment ions that allow calculation of 13C enrichment on each carbon. The technique was tested by analyzing glutamate from rat livers perfused with various 13C tracers. The labeling patterns obtained agreed with theoretical calculations or patterns reported with 14C and 13C tracers.