Quantitative determination of ochratoxin A by liquid chromatography/electrospray tandem mass spectrometry

Mass spectrometry of ochratoxin A (OTA) and B (OTB) under electrospray ioni zation (ESI) and atmospheric pressure chemical ionization (APCI) was studie d. ESI offers higher sensitivities and less fragmentation than APCI. A sens itive LC/MS/MS method for the determination of ochratoxin A (OTA) in human plasma samples was developed. The absolute minimum detection limit was arou nd 10-20 pg per injection, corresponding to 0.5 ppb in an injection equival ent to 20-40 mu g of human plasma. Ochratoxin B (OTB) was used as an intern al standard and its absence in real-life samples was carefully checked befo re samples were spiked with the internal standard. It was found that these two ochratoxins are susceptible to sodium adduct formation. Fragment ions f rom the [M + H](+) and [M + Na](+) ions of both OTA and OTB were monitored in the multiple reaction monitoring mode. Three quantitative approaches, st andard addition method, internal standard method (using ochratoxin B as an internal standard) and external standard method, were compared in the analy sis of human blood plasma. Results from the mass spectrometric method mere comparable to those from a conventional LC/fluorescence method. The LC/MS/M S method was also applied to the analysis of contaminated coffee samples. C opyright (C) 2000 John Wiley & Sons, Ltd.