Characterization of the oxidation products of paralytic shellfish poisoning toxins by liquid chromatography/mass spectrometry

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Abstract
Periodate oxidation of the toxins responsible for paralytic shellfish poisoning (PSP) yields fluorescent products that are useful for trace analysis by reversed‐phase liquid chromatography. Some toxins are oxidized to the same product, while others are transformed to a mixture of products; in ail cases, the products are too unstable to be isolated preparatively. A mobile phase containing heptafluorobutyric acid as an ion‐pair agent was developed to improve compatibility with liquid chromatography/mass spectrometry (LC/MS) analysis. Several LC/MS techniques were investigated: chemical ionization with the moving belt interface, atmospheric‐pressure chemical ionization, thermospray, continuous‐flow fast‐atom bombardment, and ion‐spray. Only LC/ion‐spray MS was able to provide spectra of the oxidized products. The products were characterized as purines resulting from: (a) breakage of the C4–C12 bond and aromatization of the remaining rings (loss of 4 hydrogens); (b) partial elimination of a carbamoyl or N‐sulfocarbamoyl side‐chain (this is promoted by the presence of an N‐1‐hydroxy group); and (c) partial hydrolysis of an N‐suifocarbamoyl side‐chain to a carbamoyl group.