Malachite green (MG) is a triphenyl methane dye that is highly efficient in battling fungi, bacteria and various single cell parasites. MG is traditionally used in aquaculture to treat and prevent fungal infections. MG, which is structurally related to known carcinogenic triphenylmethane dyes, is metabolized to leucomalachite green (LMG) and deposited in the fatty tissue of the fish. MG is under suspicion of being a human carcinogen and for causing damage to the human genetic material. Consumption of fish that is contaminated with MG is assumed to pose a significant health risk to humans. In 2003 the European Commission set the MRPL (minimum required performance limit) for MG and LMG to 2 μg/kg.

Even though malachite green is banned as a veterinary pharmaceutical for animals used for human consumption, the authorities regularly find residues of this toxic compound or its metabolites during routine checks of fish farms. The work presented in this application note describes the configuration of a combined fully automated Solid Phase Extraction (SPE) system coupled with LC/Ion Trap MS. Method parameters are shown that provide improved detection limits for the two compounds coupled with automated sample preparation for highest laboratory productivity.