Quantitative gas chromatography and single-ion detection of aliphatic α-keto acids from urine as their o-trimethylsilylquinoxalinol derivatives

A method is described for the quantitative determination of aliphatic α-keto acids in urine after derivatization with o-phenylenediamine and bis(trimethylsilyl)trifluoroacetamide, α-Ketovaleric acid and α-ketocaprylic acid are used as internal standards.The chemical yield is 80–100%. At physiological concentrations, the coefficient of variation after repeated derivatizations is 4% for pyruvic acid and 14% for α-ketoglutaric acid.With mass spectrometric single-ion detection at $\text{m}\text{c}$ = 217, 232 and 245, the biologically interesting aliphatic α-keto acids can be determined at very low levels in biological fluids.