Multiplug filtration cleanup method with multi-walled carbon nanotubes for the analysis of malachite green, diethylstilbestrol residues, and their metabolites in aquatic products by liquid chromatography-tandem mass spectrometry.

The food safety supervision in aquatic products has raised public concern in recent years. In this study, a liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method for the simultaneous quantification and identification of four residues of the ever widely used analytes (including malachite green, leucomalachite green, diethylstilbestrol, and dienestrol) in aquaculture samples was developed. For sample preparation, a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method was used, which was initially developed for pesticide residue analysis. For cleanup procedure, low-temperature cleanup method was combined with multiplug filtration cleanup (m-PFC) method based on multi-walled carbon nanotubes (MWCNTs). The volume of water, extraction solvent, cleanup sorbents, and m-PFC procedure were optimized for carp, striped bass, and giant salamander matrices. It was validated by analyzing four residues in each matrix spiked at three concentration levels of 0.5, 5, and 50 μg/kg (n = 5). The method was successfully validated according to the 2002/657/EC guidelines. After optimization, spike recoveries were within 73-106 % and <15 % relative standard deviations (RSDs) for all analytes in the tested matrices. Limits of quantification (LOQs) for the proposed method ranged from 0.10 to 0.50 μg/kg. Matrix-matched calibrations were performed with the coefficients of determination >0.998 between concentration levels of 0.5 and 200 μg/kg. The developed method was successfully applied to the determination of residues in market samples. Graphical abstract Flow chart of multi-plug filtration cleanup combined with low-temperature cleanup method.