Simultaneous measurement of ethanol and ethyl-d5 alcohol by stable isotope gas chromatography-mass spectrometry.

Efforts to define gender- and ethnic-dependent differences in ethanol first-pass metabolism by gastric mucosa and liver have been limited by a lack of analytical tools that distinguish ethanol concurrently administered by oral and intravenous routes. A stable isotope gas chromatography-mass spectrometry method for simultaneous measurement of ethanol and ethyl-d5 alcohol in serum was developed to meet this need. The assay was linear from 1 to 30 mmol/L. The limit of quantification was 1 mmol/L. Analytical imprecision (CV) was <10%. Analytical recovery was >90%. Specificity was based on retention time and reproducibility of ion ratios. The assay was free from interference by other volatile alcohols. Simultaneous oral administration of ethanol and ethyl-d5 alcohol produced nearly identical pharmacokinetic profiles. Simultaneous oral ingestion of ethanol and intravenous infusion of ethyl-d5 alcohol, adjusted for gastric emptying time, revealed decreased bioavailability of ethanol by the oral route. The method described is sufficient to study the first-pass metabolism of ethanol.