Determination of malachite green residues in rainbow trout muscle with liquid chromatography and liquid chromatography coupled with tandem mass spectrometry

A method for the determination of malachite green and its major metabolite leucomalachite green in rainbow trout muscle is reported with limits of detection of 0.8 and 0.6 mug kg(-1), respectively. Residues were extracted with an acetonitrile - acetate buffer mixture and partitioned into methylene chloride. Clean-up of the extracts was performed on alumina and propylsulfonic acid solid-phase extraction columns using the automated solid-phase extraction system. The chromatographic separation of malachite green and leucomalachite green was achieved on a Chromspher 5B column using an acetonitrile - acetate buffer mobile phase. Leucomalachite green was converted to malachite green by post-column oxidation before spectrophotometric detection at 600 nm. The mean recoveries of malachite green and leucomalachite green from control rainbow trout muscle spiked at 2 - 50 mug kg(-1) were 65% (range 63.4 - 65.9%, relative standard deviation 3.9 - 16.1%) and 74% ( range 58.3-82.6%, relative standard deviation 3.3-11.4%), respectively. Qualitative confirmation of the determined residues was performed with liquid chromatography coupled with tandem mass spectrometry detection with limits of detection of 2.5 and 1 mug kg(-1) for malachite green and leucomalachite green, respectively.