Use of immunoaffinity columns for clean-up of diarrhetic toxins (okadaic acid and dinophysistoxins) extracts from shellfish prior to their analysis by HPLC/fluorimetry

Diarrhetic Shellfish Poisoning (DSP) is a severe gastro-intestinal disease caused by consumption of seafood contaminated by microalgal toxins, mainly okadaic acid (OA) and structurally related toxins, dinophysistoxins (DTXs). Regulatory monitoring is generally based on rodent bioassays which, however, present some technical and ethical disadvantages. The most promising technique of analysis of these toxins involves an HPLC separation with spectrofluorimetric detection after derivatization of the toxins with a fluorescent reagent. The lack of specificity of the extraction procedure (liquid-liquid partition), and the presence of interfering compounds in the matrix, does not allow the determination and the quantification of low amounts of toxins in seafood. In this paper, the authors report the development and the characterization of immunoaffinity columns (IAC), which were elaborated using anti-okadaic acid monoclonal antibodies, for a specific retention of the OA group of toxins. The coupling yield and the stability of these columns were investigated as well as their capacity to remove interfering compounds. Cross-reactivity was observed between the antibodies and the DTX-1 and the DTX-2, allowing the detection of the different toxins in a single analysis. Different spiked (1 microgram OA/g) or naturally-contaminated (mussel digestive gland: 2 micrograms OA/g; algae: 165 micrograms OA/g) matrices were tested. The recovery for OA varied from 55 to 95% according to the matrices. The IAC purification was then included as a step of a global [IAC/HPLC/spectrofluorimetric detection] method and the performance of the method was evaluated. Estimations of the linearity and the accuracy (percentages of the presumptive response for OA in the range +101% to +114%) were satisfactory in accordance with the method validation criteria.