DETECTION OF OKADAIC ACID-ESTERS IN THE HEXANE EXTRACTS OF SPANISH MUSSELS

Two types of low polar derivatives of OA and dinophysitoxins have been reported in shellfish or in phytoplankton: 7-O-acyl esters containing a fatty acyl group attached through the 7-OH group and diol esters in which the carboxylic group of the toxins has been esterified. These c ompounds cannot be directly detected by liquid chromatography and fluo rimetric detection as 9-anthryldiazomethane derivatives, owing in the first case to their low polarity and high molecular weight, and in the second case because they have the carboxylic group esterified. All of them must be hydrolysed before derivatization to be detected as Adam derivatives of the corresponding non-acylated toxins. In the Lee proce dure, after extraction of the shellfish digestive glands with 80% meth anol, a liquid-liquid partition with a non-polar solvent such as hexan e is carried out in order to remove non-polar lipids. The presence of non-polar toxins was investigated in Spanish mussels and confirmed in the hexane layer, usually discarded in conventional extraction procedu res, by analysis of the alkaline hydrolysis products. A preferred solu bilization of these toxins in a non-polar solvent like hexane is repor ted. The inclusion of a hydrolytic step of the hexane extract in the g eneral procedure is suggested in order to monitor the contribution of non-polar diarrhoetic shellfish poisons (DSPs) to the total DSP shellf ish toxicity. This is the first report of DSPs other than OA and DTX2 in Spanish mussels.