Full Description ADOPTED_FROM:EN 14526:2017 This European standard specifies a method [1] for the quantitative determination of saxitoxin (STX), decarbamoyl saxitoxin (dcSTX), neosaxitoxin (NEO), decarbamoyl neosaxitoxin (dcNEO), gonyautoxin 1 and 4 (GTX1,4; sum of isomers), gonyautoxin 2 and 3 (GTX2,3; sum of isomers), gonyautoxin 5 (GTX5 also called B1), gonyautoxin 6 (GTX6 also called B2), decarbamoyl gonyautoxin 2 and 3 (dcGTX2,3; sum of isomers), N-sulfocarbamoyl-gonyautoxin 1 and 2 (C1,2; sum of isomers) and (depending on the availability of certified reference materials (CRMs)) N-sulfocarbamoyl-gonyautoxin 3 and 4 (C3,4; sum of isomers) in (raw) mussels, oysters, scallops and clams. Laboratory experience has shown that it is also be applicable in other shellfish [2], [3] and cooked shellfish products. The method described was validated in an interlaboratory study [4], [5] and was also verified in a EURL-performance test aiming the total toxicity of the samples [6]. Toxins which were not available in the first interlaboratory study [4], [5] as dcGTX2,3 and dcNEO were validated in two additional interlaboratory studies [7], [8]. The lowest validated levels [4], [5], [8], are given in µg toxin (free base) per kg shellfish tissue and also as µmol/kg shellfish tissue and are listed in Table 1. A quantitative determination of GTX6 (B2) was not included in the first interlaboratory study but several laboratories detected this toxin directly after solid phase extraction with ion-exchange (SPE-COOH) clean-up and reported a mass concentration of 30 µg/kg or higher in certain samples. For that reason, the present method is applicable to quantify GTX6 (B2) directly, depending on the availability of the standard substance. Currently it is possible to determine GTX6 after a hydrolysis of Fraction 2 of the SPE-COOH clean-up, described in 6.4 as NEO. The indirect quantification of GTX6 was validated in two additional interlaboratory studies [7], [8]. A quantitative determination of C3,4 was included in the first interlaboratory study. The present method is applicable to quantify C3,4 directly, depending on the availability of the standard substance. If no standard substances are available, C3,4 can only be quantified as GTX1,4 if the same hydrolysis protocol used for GTX6 (6.4) is applied to Fraction 1 of the SPE-COOH clean-up, see [10].