Potential lack of specificity using electrospray tandem-mass spectrometry for the analysis of mycophenolic acid in serum

The remarkably strong formation of the mycophenolic acid molecular ion from mycophenolic acid glucuronide during electrospray atmospheric pressure ion ization in patients' serum samples is described. It is concluded that becau se of this effect appropriate chromatographic separation prior to tandem-ma ss spectrometric analysis and correct peak detection and integration of the respective multiple reaction monitoring traces is mandatory probably in al l cases where conjugate drug metabolites are present in post-dose samples.