Liquid chromatography with electrospray ion trap mass spectrometry for the determination of five azaspiracids in shellfish.

Azaspiracid poisoning (AZP) is a new human toxic syndrome that is caused by the consumption of shellfish that have been feeding on harmful marine microalgae. A liquid chromatography-mass spectrometry (LC-MS) method has been developed for the determination of the three most prevalent toxins, azaspiracid (AZA1), 8-methylazaspiracid (AZA2) and 22-demethylazaspiracid (AZA3) as well as the isomeric hydroxylated analogues, AZA4 and AZA5. Separation of five azaspiracids was achieved on a C18 column (Luna-2, 150 x 2 mm, 5 microm) with isocratic elution using acetonitrile-water containing trifluoroacetic acid and ammonium acetate as eluent modifiers. Using an electrospray ionisation (ESI) source with an ion-trap mass spectrometer, the spectra showed the protonated molecules, [M+H]+, with most major product ions due to the sequential loss of two water molecules. A characteristic fragmentation pathway that was observed in each azaspiracid was due to the cleavage of the A-ring at C9-C10 for each toxin. It was possible to select unique ion combinations to distinguish between the isomeric azaspiracids, AZA4 and AZA5. Highly sensitive LC-MS3 analytical methods were compared and the detection limits were 5-40 pg on-column. Linear calibrations were obtained for AZA1 in shellfish in the range 0.05-1.00 microg/ml (r2 = 0.9974) and good reproducibility was observed with a relative standard deviation (%RSD) of 1.8 for 0.9 microg AZAI/ml (n=5). The %RSD values for the minor toxins, AZA4 and AZA5, using LC-MS3 (A-ring fragmentation) were 12.3 and 8.1 (0.02 microg/ml; n=7), respectively. The selectivity of toxin determination was enhanced using LC-MS-MS with high energy WideBand activation.