Simultaneous determination of antipyrine, 4-hydroxyantipyrine, 3-hydroxymethylantipyrine and norantipyrine in urine by gas chromatography chemical ionization mass spectrometry.

A simple, accurate and precise procedure was developed to quantify, in a single run, antipyrine, 4-hydroxyantipyrine, 3-hydroxymethylantipyrine and norantipyrine in urine. The stable isotope-labelled internal standards for the assay were obtained from a subject who ingested deuterium labelled antipyrine and produced urine containing the labelled drug and metabolites.