Multiresidue method for the triphenylmethane dyes in fish: Malachite green, crystal (gentian) violet, and brilliant green

Abstract

Liquid chromatographic methods are presented for the quantitative and confirmatory determination of crystal violet (CV; also known as gentian violet), leucocrystal violet (LCV), brilliant green (BG), and leucobrilliant green (LBG) in catfish. LCV and LBG were oxidized to the chromic CV and BG by reaction with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, and residues were measured as the combined CV ± LCV and BG ± LBG. These methods are extensions of published methods for malachite green (MG) analysis to allow simultaneous determination of MG, CV, and BG. Residues were extracted from muscle with ammonium acetate buffer and acetonitrile, and extracts cleaned up using dichloromethane partitioning and solid-phase extraction. Extracts were analyzed by liquid chromatography with visible detection (LC-VIS). The method was validated for catfish fortified with LCV over the range 0.25–10 ng g −1 and CV at 2 ng g −1. Average recoveries were 90.6% (±8.1% R.S.D., n = 45) for LCV and 84.4% (±4.2% R.S.D., n = 6) for CV. The average recovery for samples fortified with BG or LBG over the range 0.5–10 ng g −1 was 67.2% (±14.8% R.S.D., n = 31). CV and BG were confirmed in fish extracts by ion trap LC–mass spectrometry (LC–MS n ) with no discharge-atmospheric pressure chemical ionization. Average LC–MS n recoveries were 96.5, 96.6, and 70.2% for samples fortified with CV, LCV, and BG or LBG. The limits of detection for CV, BG, and MG were in the range of 0.07–0.24 ng g −1 (ppb) for the two different instrumental methods. This methodology was applied to the analysis of catfish treated with CV and BG.