Simultaneous quantification of antibiotic dyes in aquatic products and feeds by liquid chromatography–tandem mass spectrometry

A confirmatory and quantitative method based on liquid chromatography–tandem mass spectrometry (LC/MS/MS) has been developed for the determination of low-level residues of three antibiotic dyes and two metabolites in fish muscle and feed. The target compounds include methylene blue (MB), crystal violet (CV), leucocrystal violet (LCV), malachite green (MG), and leucomalachite green (LMG). The procedures involve solvent extraction by 50% McIlvaine’s buffer with acetonitrile, followed by solid phase extraction (SPE) with an MCX cartridge. High performance liquid chromatography (HPLC) and positive electrospray ionization (ESI) MS with multiple reaction monitoring of two transition reactions was applied for each compound. The detected ion ratios of MB, CV, LCV, MG, and LMG were 11.8, 34.9, 88.4, 25.6, and 42.0, respectively. The average fortification recoveries of the MB, CV, LCV, MG, and LMG of the level of 0.8 μg/kg tested in fish muscle and feed samples were 99.68, 98.93, 100.49, 100.01, and 100.00%, respectively. The precision of analysis of analytes in fish muscle and feed ranged from 4% to 14% and from 7% to 14%, respectively. The decision limits (CCα) were 0.28–0.54 μg/kg, and the detection capabilities (CCβ) were 0.35–0.67 μg/kg (n = 99).