Simultaneous determination of glutathione and cysteine concentrations and 2H enrichments in microvolumes of neonatal blood using gas chromatography-mass spectrometry

A method is described whereby the concentrations and H-2 isotope enrichment of glutathione (GSH) and cysteine can be simultaneously determined in a single gas chromatography-mass spectrometry run following derivatization as their N,S-ethoxycarbonyl methyl esters. Improvements of the derivatization protocol and the use of a short gas chromatography column combined with single-ion monitoring allow for rapid quantification of these parameters with acceptable precision and reproducibility (coefficient of variation less than 5%). The method makes possible their quantitative measurement in very small volumes (50 mu L) of human umbilical cord blood, and is thus suitable for determining the cysteine and GSH concentrations and H-2 isotope enrichments in blood samples from neonates or in other conditions in which sample size is restricted. It is shown that the fractional synthesis rate of human umbilical erythrocyte lysates in vitro is several-fold greater than that measured in vivo.