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More than 20 analogues of saxitoxin occur naturally. An accurate analytical method applicable to all saxitoxins is required because of the recent findings that decarbamoyl toxins and C (N-sulfocarbamoyl- 11-hydroxysulfate) toxins are metabolites of marine animals or major products of some dinoflagellate species. Almost all the toxins could be determined by ion-interaction chromatography on a silica-based reversed-phase (C8) column with postcolumn periodate oxidation and fluorescence detection. Toxin groups of different net charges were separately determined by isocratic elution using different mobile phases. For determination of the saxitoxin group (net charge, 2+) and the gonyautoxin group (net charge, 1+), use of 1-heptanesulfonate as counterion, with or without acetonitrile in the mobile phase, resulted in resolution of decarbamoyl toxins from their carbamate analogues. C toxins having both M-sulfocarbamoyl and 11-hydroxysulfate moieties on the same molecule were completely resolved using the tetrabutylammonium ion. High sensitivity with detection limits ranging from 20 to 110 fmol were achieved as a result of reduced band broadening and optimized reaction conditions. For applications to biological matrixes, a cleanup procedure using a C18 solid-phase extraction cartridge was effective in preventing false peaks. When applied to low-toxicity shellfish, the liquid chromatographic method gave higher values than the standard mouse bioassay, because of underestimation by the bioassay.

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