Confirmation of domoic acid in shellfish using butyl isothiocyanate and reversed-phase liquid chromatography.

A simple chemical confirmatory technique has been developed for domoic acid, a neurotoxic amino acid of marine origin. After extraction with water-methanol, the domoic acid-containing extract is analysed directly by reversed-phase liquid chromatography with UV absorption detection at 242 nm. For confirmation of positive results an aliquot of the extract is evaporated to dryness and reacted with butyl isothiocyanate to form a thiourea derivative which elutes later than underivatized domoic acid. No additional sample cleanup is required in order to carry out the derivatization for conformation of domoic acid at the Canadian 20 micrograms/g guideline level in shellfish. In mussel extract, domoic acid was converted to the thiourea derivative with a yield of 86-91% compared to a pure standard carried through the same reaction. The detection limit for the derivative was about 5-10 micrograms/g of equivalent domoic acid in extracts of mussels, clams or oysters.