The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. I: Interlaboratory studies of methods of analysis

This paper describes the first part of a project undertaken to develop muss el reference materials for Paralytic Shellfish Poisoning (PSP) toxins. Two interlaboratory studies were undertaken to investigate the performance of t he analytical methodology for several PSP toxins, in particular saxitoxin ( STX) and decarbamoyl-saxitoxin (dc-STX) in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the second part of the project: the certification exercise. In the first study, 18 laborat ories were asked to measure STX and dc-STX in rehydrated lyophilized mussel material and to identify as many, other PSP toxins as possible with a meth od of their choice. In the second interlaboratory study, 15 laboratories we re additionally asked to determine quantitatively STX and dc-STX in rehydra ted lyophilized mussel and in a saxitoxin-enriched mussel material. The fir st study revealed that three out of four postcolumn derivatization methods and one pre-column derivatization method sufficed in principle to determine STX and dc-STX. Most participants (13 of 18) obtained acceptable calibrati on curves and recoveries. Saxitoxin was hardly detected in the rehydrated l yophilized mussels and results obtained for dc-STX yielded a CV of 58% at a mass fraction of 1.86 mg/kg. Most participants (14 out of 18) identified g onyautoxin-5 (GTX-5) in a hydrolysed extract provided. The first study, led to provisional criteria for linearity, recovery and separation. The second study revealed that 6 out of 15 laboratories were able to meet these crite ria. Results obtained for dc-STX yielded a CV of 19% at a mass fraction of 3.49 mg/kg. Results obtained for STX in the saxitoxin-enriched material yie lded a CV of 19% at a mass fraction of 0.34 mg/kg. Saxitoxin could not be d etected in the PSP-positive material. Hydrolysis was useful to confirm the identity of GTX-5 and provided indicative information about C1 and C2 toxin s in the PSP-positive material. The methods used in the second interlaborat ory study showed sufficiently consistent analysis results to undertake a ce rtification exercise to assign certified values for STX and dc-STX in lyoph ilized mussel.