Stable isotope dilution mass spectrometry for the diagnostic study of histidinaemia

Stable isotope dilution mass spectrometry for a diagnosis to detect the heterozygote state of histidinaemia has been developed. We have synthesized L-[3-15N, 5,beta,beta-2H3]histidine (histidine-[M + 4]) for use as a biological internal standard and DL-[1,3-15N2, 5,alpha,beta,beta-2H4]histidine (histidine-[M + 6]) as an analytical internal standard. For the gas chromatographic/mass spectrometric assay of stable isotopically substituted histidine in human plasma, histidine was derivatized to alpha N-trifluoroacetyl-imN-ethoxycarbonylhistidine n-butyl ester. Quantification was carried out by selected ion monitoring on the molecular ions (m/z 379, 383 and 385) of the respective gas chromatographic derivatives of non-labelled histidine, histidine-[M + 4] and histidine-[M + 6]. The calibration curve was linear over the range of 5-2000 ng ml-1 plasma (r = 0.9999). The intra- and inter-assay coefficients of variation were in the range 1.1-3.9%. The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for application to a pharmacokinetic study of histidine after administration of a trace amount of stable isotopically substituted histidine in man.