Simultaneous determination of malachite green, crystal violet, methylene blue and the metabolite residues in aquatic products by ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry

This work describes solid-phase extraction-ultra-performance liquid chromatography with electrospray ionization tandem spectrometry for determination of malachite green and metabolite leucomalachite green, crystal violet and metabolite leucocrystal violet, methylene blue and metabolites including azure A, azure B and azure C in aquatic products. Samples were extracted with acetonitrile and ammonium acetate buffer and purified by liquid extraction with dichloromethane, and then on MCAX solid-phase extraction cartridges. Then the extract was evaporated at 45°C by nitrogen blow. The residue was dissolved and separated by an Acquity BEH C18 column. The mobile phase was acetonitrile (A) and 5 mmol/L of ammonium acetate containing 0.1% formic acid (B). Analytes were confirmed and quantified using a tandem mass spectrometry system in multiple reaction mode with triple quadrupole analyzer using positive polarity mode. The limits of detection of malachite green, leucomalachite green, crystal violet and leucocrystal violet were 0.15 μg/kg, the limits of quantification were 0.50 μg/kg, and the average recoveries were more than 75% with spiked residues from 0.5 to 10 μg/kg. The relative standard deviations were less than 13%. The limits of detection of methylene blue, azure A, azure B and azure C were 0.3 μg/kg, the limits of quantification were 1.0 μg/kg, the average recoveries were more than 70% with spiked residues from 1.0 to 10 μg/kg and the relative standard deviations were less than 15%. The method has the merits of simplicity, sensitivity and rapidity, and can be used for simultaneous determination of the analytes in aquatic products.