ANALYSIS OF MALACHITE GREEN AND METABOLITES IN FISH USING LIQUID-CHROMATOGRAPHY ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION MASS-SPECTROMETRY

Malachite green (MG), a traditional agent used in aquaculture, is stru cturally related to other carcinogenic triphenylmethane dyes. Although MG is not approved for use in aquaculture, its low cost and high effi cacy make illicit use likely. We developed sensitive and specific meth ods for determination of MG and its principal metabolite, leucoMG (LMG ), in edible fish tissues using isotope dilution liquid chromatography atmosphere pressure chemical ionization mass spectrometry. MG and LMG concentrations were measured in filets from catfish treated with MG u nder putative use conditions (ca, 250 and 1000 ppb, respectively) and from commercial trout samples (0-3 and 0-96 ppb, respectively). Concen trations of LMG in edible fish tissues always exceeded those of MG. A rapid cone voltage switching acquisition procedure was used to simulta neously produce molecular ions for quantification and diagnostic fragm ent ions for confirmation of MG and metabolites. The accurate and prec ise agreement between diagnostic ion intensity ratios produced by LMG in authentic standards and incurred fish samples was used to unambiguo usly confirm the presence of LMG in edible fish tissue. This suggested the validity of using LMG as a marker residue for regulatory determin ation of MG misuse. Additional metabolites derived from oxidative meta bolism of MG or LMG (demethylation and N-oxygenation) were identified in catfish and trout filets, including a primary arylamine which is st ructurally related to known carcinogens, The ability to simultaneously quantify residues of MG and LMG, and to confirm the chemical structur e of a marker residue by using LC/MS, suggests that this procedure may be useful in monitoring the food supply for the unauthorized use of M G in aquaculture. (C) 1998 John Wiley & Sons, Ltd.