Determination of the sum of malachite green and leucomalachite green in salmon muscle by liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry.

A sensitive method for the determination and confirmation of the sum of malachite green (MG) and leucomalachite green (LMG) in salmon muscle has been developed. It is based on the use of an oxidative pre-column reaction which converts LMG into MG previous to liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry (LC-APCI-MS) analysis. The determination of both compounds together constitutes a good screening method to confirm the presence of this kind of residue, taking into account that the combined signals will provide a gain of sensitivity. The detection limit, determined for spiked salmon samples using the confirmatory ion m/z 313, was 0.15 microg/kg. The recoveries determined at a spiking level of 2 microg/kg were 85 and 70% for LMG and MG, respectively, with respective relative standard deviations of 1.3 and 3.1%.