Abstract: Measurement of Plasma KIC by Stable Isotope Dilution-Negative Chemical Ionization Gas Chromatography/Mass SpectrometryDai Tengchang;Shi Ju;Xia Zongqin(Shanghai Second Medical University,Shanghai 200025,China)Abstract:α-ketoisocaproate(KIC)is the metabolic product of leucine.Using D3-KIC as the internal standard of isotope dilution,the KIC in human plasma were converted to its pentafluorobenzyl ester and analysed with methane negative chemical ionization gas chromatography/mass spectrometry.The intra-batch and inter-batch coefficients of variation were 0.79% and 0.78% respectively.The mean concentration of plasma KIC of 10 normal adult volunteers was 44.07±2.87 μmol/L.Keywords:gas chromatography/mass spectrometrry,negative chemical ionization,stable isotope dilution analysis,α-ketoisocaproate