Multiresidue determination of triarylmethane and phenothiazine dyes in fish tissues by LC–MS/MS

The occurrence of residues of malachite green and its leuco-metabolite in tissues of farmed fish for human consumption have long been of concern and there is extensive literature on methods of analysis and surveillance for these compounds. Recently, concern has been expressed that the use of other related compounds in place of malachite green may go undetected. This paper describes a new method for extending the range of triarylmethane and related phenothiazine dyes that can be detected in fish. In this procedure 13 parent compounds are monitored, with any potential leuco-forms being oxidized back to the parent prior to determination. The method utilizes a buffer–acetonitrile extraction followed by liquid–liquid extraction. Oxidant is added and the extracts further purified by cation exchange chromatography. Final determination is carried out using LC–MS/MS. The method has been validated to the standards of Commission Decision 2002/657/EC.