LIQUID-CHROMATOGRAPHY WITH FLUOROMETRIC, MASS-SPECTROMETRIC AND TANDEM MASS-SPECTROMETRIC DETECTION FOR THE INVESTIGATION OF THE SEAFOOD-TOXIN-PRODUCING PHYTOPLANKTON, DINOPHYSIS-ACUTA

The diarrhoeic shellfish poisoning (DSP) toxins, okadaic acid (OA) and its isomer, dinophysistoxin-2 (DTX-2), were determined in the marine phytoplankton, Dinophysis acuta, harvested in Ireland. Unialgal sample s (22-100 cells) were extracted and derivatised using 9-anthryldiazome thane (ADAM) or 1-bromoacetylpyrene (BAP) and analysed by Liquid chrom atography (LC). Isocratic elution on a C-18 reversed-phase column, wit h fluorimetric detection, was used to determine OA (58+/-7 pg/cell) an d DTX-2 (78+/-14 pg/cell). The detection limit was 0.1 ng OA/20 mu l i njection using ADAM. Gradient LC, using a polymeric bonded phase, succ essfully separated mixtures containing both the ADAM and BAP derivatis ed toxins. Identification of DSP toxins was confirmed using isocratic micro LC with tandem mass spectrometric (mu LC-MS-MS) analysis of the free toxins and mu LC-MS of the BAP-derivatised toxins with an ionspra y (IS) interface, coupled to an atmospheric pressure ionisation (API) source. Collision induced dissociation (CID) ion mass spectra of the p rotonated molecule, [M+H](+), at mit 805 for OA and DTX-2, identified three diagnostic fragment ions for each analyte which were used for se lected reaction monitoring (SRM) LC-MS-MS analysis. The detection limi t for OA and DTX-2 was 0.025 ng/0.2 mu l injected. These studies showe d that D. acuta was the progenitor of DTX-2 in shellfish. (C) 1997 Els evier Science B.V.