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 ionization in patients' serum samples is described. It is concluded that because of this effect appropriate chromatographic separation prior to tandem-mass spectrometric analysis and correct peak detection and integration of the respective multiple reaction monitoring traces is mandatory probably in all cases where conjugate drug metabolites are present in post-dose samples.