Glutamine and glutamate: automated quantification and isotopic enrichments by gas chromatography/mass spectrometry.
A method is described for simultaneous quantification of glutamine and glutamate plasma levels and isotopic enrichments in these compounds. Glutamine and glutamate are analyzed intact as their tertiary-butyldimethylsilyl derivatives. Deuterated glutamine and glutamate are used as internal standards for quantification by reverse isotope dilution. Preparation of plasma samples is accomplished by adding ammonium formate as an ion-pairing agent followed by extraction of the amino acids into 4.3:1 methanol:water. Negligible amounts of glutamine to glutamate conversion are observed during the sample preparation and GC/MS analysis. Since glutamine is analyzed intact, both single and double [15N]glutamine labels can be quantified. [15N]Glutamine at 0.2 to 11 mol% excess was measured in plasma with an average relative standard error of 3.8%, and [15N]glutamate over a range of 0.4 to 9 mol% excess was measured with a mean relative standard error of 12%. At glutamate levels above 1 mol% excess 15N, the mean relative standard error was 6%. Finally, automated sample injection into the GC/MS and automated data reduction are used for the analysis of samples by GC/MS.
D000818:Animals; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D005971:Glutamates / Q000097:blood*; D018698:Glutamic Acid; D005973:Glutamine / Q000097:blood*; D009587:Nitrogen Isotopes; D011761:Pyrrolidonecarboxylic Acid / Q000097:blood; D051381:Rats
D005971:Glutamates; D009587:Nitrogen Isotopes; D005973:Glutamine; D018698:Glutamic Acid; D011761:Pyrrolidonecarboxylic Acid