| Abstract | Reference materials play a very important role in analytical laboratories. They are used for calibration of instruments, development and validation of measurement methods, and routine assessment of method performance. Certified reference materials (CRMs) are essential for laboratories maintaining a quality system such as ISO-17025 because they ensure accuracy and traceability to international standards. The NRC-IMB Certified Reference Materials Program (CRMP) produces CRMs for shellfish toxins and distributes them on a not-for-profit basis. Diarrhetic shellfish poisoning (DSP) is a gastrointestinal illness caused by ingestion of shellfish contaminated with toxins produced by certain species of dinoflagellates. The principal toxins associated with DSP are okadaic acid (OA) and the dinophysistoxins, DTX1 and DTX2. The most common methods of analysis for these toxins are based upon liquid chromatography with either mass spectrometric (LC-MS) or fluorescence detection (LC-FLD). Accurate calibration is an essential step in such analyses, particularly for regulatory work. Two CRMs for DSP toxins are currently available from CRMP: (a) CRM-OA-b, a certified calibration solution for OA; and (b) CRM-DSP-Mus-b, a certified mussel tissue CRM for OA and dinophysistoxin-1. Two other calibration solution CRMs are in preparation for DTX1 and DTX2. OA, isolated from Prorocentrum lima, was carefully assessed for its purity by LC-MS and nuclear magnetic resonance (NMR). An exhaustive study of OA stability was performed in various solvents and under different conditions. Based on this work, methanol was selected as the best solvent. NMR was then used to measure the absolute concentration of OA in a CD3OH stock solution, which was then diluted very accurately in degassed, high purity methanol to a concentration of 20 µmol L-1. Aliquots were dispensed into argon-filled glass ampoules, which were immediately flame-sealed. The mussel tissue CRM was produced by blending blue mussel (Mytilus edulis) digestive glands with a small amount of P. lima. The CRM (~4 grams of homogenate) is distributed in polypropylene bottles that were heat sealed, thermally sterilized and individually packed in trilaminate pouches. The toxin levels in this CRM were determined to be 10.1 mg/kg for OA and 1.3 mg/kg for DTX1 using LC-MS and LC-FLD after derivatization with 9-anthryldiazomethane (ADAM). |
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