Post-Column Electrochemical Oxidation of Leuco Malachite Green for the Analysis of Rainbow Trout Flesh Using HPLC with Absorbance Detection

Malachite green is a dye used in aquaculture as a parasiticide. A method is described for the quantitation of residues of malachite green and its colourless reduced form, leuco malachite green, in the flesh of rainbow trout. The analytes are extracted with solvent and purified using a C18 solid phase extraction cartridge. Determination of both compounds by reversed phase HPLC with absorbance detection at 610 nm is achieved following post-column oxidation of the leuco form to malachite green using an electrochemical detector cell. The limits of detection for malachite green and leuco malachite are 6 ng/g and 3 ng/g, respectively. At concentrations from 25–200 ng/g, recoveries in the range 73–87% were achieved for malachite green and 89–98% for leuco malachite green. Oxidation of leuco malachite green using activated charcoal is also described as as an alternate manner of determining total malachite green.