PARALYTIC SHELLFISH POISON REFERENCE MATERIALS - AN INTERCOMPARISON OF METHODS FOR THE DETERMINATION OF SAXITOXIN

Within the framework of the European Commission's Measurements and Tes ting Programme (BCR) a project has been undertaken to develop shellfis h reference materials for Paralytic Shellfish Poisons (PSP). In a prel iminary phase of the project, an intercomparison study of methods was undertaken. In this exercise 18 laboratories were asked to analyse sol utions of saxitoxin and PSP-containing shellfish extracts with a metho d of their choice. The study revealed that: all the methods considered (four HPLC methods, one ELISA method) were in principle adequate for the quantification of saxitoxin in solution in the absence of interfer ing substances (Coefficient of variation (CV) 33% at a concentration o f 0.5 mug/ml); three of the HPLC methods used were able to quantify sa xitoxin in PSP-positive mussel extract, the fourth method gave signifi cant overestimation; the CV of all HPLC results was 53% at a mean saxi toxin mass fraction of 2.06 mg/kg mussel meat, the recoveries varied f rom 59-173%; and the ELISA method grossly overestimated the saxitoxin content in mussel extract, probably due to cross reactions of the anti bodies with other PSP. The feasibility of preparing a homogeneous batc h of ampouled mussel extracts (CV 3.5% at a saxitoxin concentration of approximately 1.5 mg/kg shellfish), sufficiently stable for at least 4 months storage both at 4-degrees-C and approximately 20-degrees-C, w as demonstrated. The performance of the different methods for the anal ysis of PSP other than saxitoxin has not yet been evaluated, due to th e current lack of PSP standards. Some of the problems observed in the intercomparison study were partly due to the nature of the chromatogra phic columns used, the composition of the HPLC mobile phase (pH, ion s trength), non-optimal conditions for derivatization and matrix interfe rence. Following the outcome of this study, a three year multistage pr oject involving 15-20 European laboratories has been initiated, aimed at improving the accuracy and comparability of PSP measurements as wel l as preparing reference materials for PSP.