Identification of conjugated metabolites of antipyrine in urine by pyrolysis-electron-impact mass spectrometry

Abstract

Pyrolysis-electron-impact mass spectrometry can be employed as a fast and sensitive method for the identification of unconjugated and conjugated metabolites of antipyrine at different stages of the work-up procedure. The method avoids derivatization of the highly polar conjugates, generally a basic requirement for electron-impact investigation. Using crude extracts of human and rat urine, endogeneous products of the metabolic process did not interfere with the studied metabolite. It is demonstrated that all phase-I metabolites so far described in the literature can be thermally liberated from their corresponding conjugates and subsequently identified by electron-impact mass spectrometry. The isomeric main metabolites 3-hydroxymethylantipyrine and 4-hydroxyantipyrine can be distinguished by specific pyrolytic reactions. The different temperatures of decomposition of the conjugated sulphates and glucuronides give additional information on the nature of the conjugates. Thus, the characteristic difference in the metabolic patterns in man and rat is reflected in the mass thermograms of the aglycones obtained by thermal decomposition of the conjugate mixtures.