Gas Chromatography/Mass Spectrometry Determination of Urea in Plasma and Application to Urea Metabolism Study

Article abstract of DOI:10.1021/ac00240a031

The study of urea metabolism in human necessitates sensitive methods, so that very low isotopic enrichments of plasma or urinary urea can be measured.A stable derivative of urea, suitable for the measurements of 15N or 13C enrichments of urea using gas chromatography/mass spectrometry, is described.The trimethylsiloxypyrimidine could be used to measure <15N2>- and <15N1>urea enrichments as low as 0.5percent with a coefficient of variation below 5percent.Determination of a lower enrichment of <15N2>urea required the use of 2-trifluoroacetoxypyrimidine, which had a background of0.4 percent at the (M+2) ion.The coefficient of variation in determining the background was 1.6percent; this means a low enrichment, such as 0.1percent, could be determined with confidence.This technique was applied to the study of urea metabolism in humans and dogs.