Analysis of domoic acid and related compounds by mass spectrometry and gas chromatography/mass spectrometry as N-trifluoroacetyl-O-silyl derivatives

A method is presented for the analysis of shellfish tissue for domoic acid, a neurotoxic amino acid responsible for cases of amnesic shellfish poisoning. Tissue extracts are first taken through a two-stage solid-phase extraction clean-up, using reversed-phase and strong cation exchange cartridges. A two-stage derivatization, using N-methyl-bis-trifluoroacetamide followed by either N-methyl-tert-butyldimethylsilyltrifluoroacetamide or N, O-bis-trimethylsilyltrifluoroacetamide, is then used to produce an N-trifluoroacetyl-O-silyl derivative which can be analyzed by mass spectrometry with introduction via direct inlet probe, moving-belt liquid chromatograph/mass spectrometer interface, or capillary column gas chromatography. The N-trifluoroacetyl-O-tert-butyldimethylsilyl derivative, which has good stability towards hydrolysis, provides a spectrum well suited to gas chromatography/mass spectrometry (GC/MS) using selected ion recording. GC/MS data for two related compounds, kainic acid and dihydrokainic acid, are also reported. The latter is used as an internal standard for quantification of domoic acid, although the method reported is intended primarily for confirmation of the toxin and related compounds in shellfish tissue.