Screening and confirmation of triphenylmethane dyes and their leuco metabolites in trout muscle using HPLC-vis and ESP-LC-MS

An extraction and clean-up protocol for the determination of Malachite Green and Crystal Violet and the corresponding leuco compounds in trout muscle has been developed. Final determination is by HPLC with visible (screening) or ESP-MS (confirmation) detection. In both cases lead(IV) oxide was used on-line to oxidise the leuco compounds back to the parent after chromatographic separation and prior to detection. The procedure was validated down to 2 micrograms kg-1. Intra- and inter-batch precision was measured at 3 levels for all compounds. Recoveries were in the range 66-116% with RSD of 1-17% for determination by HPLC with visible detection. For LC-MS determination, recoveries were in the range 61-94% with RSD of 4-15%. Limited surveillance data indicated that Malachite Green usage was more effectively monitored by including the leuco compound as well as the parent (9 positives for the leuco compound as opposed to 1 for Malachite Green out of 31 samples analysed).