| Résumé | Paralytic shellfish poisoning (PSP) toxins are potent neurotoxins, produced by several marine dinoflagellates. These toxins are tetrahydropurine derivatives based on the parent compound, saxitoxin (STX), and can be divided into three classes: carbamate, N-sulfocarbamoyl and decarbamoyl toxins. Many structural analogs have been identified. They all have different toxicities, with the carbamate toxins being the most toxic and the N-sulfocarbamoyl toxins being the least toxic. An important issue with PSP toxins is the potential for inter-conversion of individual toxins, through epimerization, desulfation or decarbamoylization, due to conditions (acidity, heat) used in extractions or due to metabolism in shellfish. Since the specific toxicity of PSP toxins vary widely, inter-conversions can lead to dramatic differences in calculated toxicity of samples. This presentation will cover our work on the evaluation of various extraction methods for PSP toxins from shellfish tissues. The aim is to find the best method(s) for preparing samples for the analysis of PSP toxins in routine regulatory laboratories. In addition, we need extraction methods for our work on the development of a certified reference material (CRM). Extraction procedures for regulatory monitoring need to be rapid and cost effective. For the certification of a reference material, however, extraction procedures must give excellent recovery, accuracy and precision, while issues such as cost and speed are not so critical. Ideally two complementary extraction methods are also required for certification studies. For both applications, it is important to ensure minimal inter-conversion of toxins during the extraction process, or at the very least, to carefully control the degree of conversion. Different solvents ranging from 0.1 M HCl and 1% acetic acid to organic solvents have been examined. The effects of extracting with or without heating have also been studied. A microwave digestion procedure proved very useful as an alternative to the traditional hot plate method. Rapid dispersive liquid-solid extractions were compared with exhaustive procedures. An entirely different procedure called matrix solid phase dispersion has also been developed. This holds promise as a useful method as it incorporates cleanup, filtration and extraction in one procedure. |
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