Location of functional groups in antipyrine metabolites by mass spectrometry

The mass spectra of antipyrine metabolites show characteristic fragmentation patterns which depend on the presence and position of functional groups. A substituent at position 4 is indicated by an intense key fragment at m/e 56 and a substituent at the methyl group in position 3 causes a significant increase in the intensity of the peak at m/e 82. The fragment at m/e 96, which is characteristic for antipyrine itself, is suppressed if there is a substituent in either position 3 or 4. Mass spectra of the glucuronides of 4-hydroxyantipyrine and 3-hydroxymethylantipyrine are also discussed.