Simultaneous determination of malachite green, gentian violet and their leuco metabolites in catfish or trout tissue by high-performance liquid chromatography with visible detection

A sensitive analytical procedure for the determination of residues of leucomalachite green (LMG)-malachite green (MG) and leucogentian violet (LGV)-gentian violet (GV) in catfish or trout tissue is presented. Frozen (-20 degrees C) fish fillets were cut into small pieces and blended in a Waring blender. A 20-g amount of homogenized fish tissue was extracted with acetonitrile-buffer, partitioned against methylene chloride, and cleaned up on tandem neutral alumina and propylsulfonic acid cation-exchange solid-phase extraction cartridges. Samples of 100 mu l (0.8 g equiv.) were chromatographed isocratically in 10 min using an acetonitrile-buffer mobile phase on a short-chain deactivated (SCD) reversed-phase column (250x4.6 mm I.D.) in-line with a post-column PbO2 oxidation reactor. The PbO2 post-column reactor efficiently oxidized LMG to the chromatic MG, and LGV to the chromatic GV permitting visible detection at 588 nm for all four compounds. Linearity was demonstrated with standards over the range of 0.5-50 ng per injection. Recoveries of LMG, MG, LGV and GV from catfish tissues fortified at 10 ng/g were 75.4+/-3.0, 61.3+/-4.1, 72.6+/-3.7 and 87.9+/-2.5, respectively, while trout tissues fortified at 10 ng/g yielded recoveries of 82.6+/-2.3, 48.6+/-1.8, 72.1+/-2.1 and 83.8+/-4.6 (mean+/-S.D., n=4), respectively.