Determination of malachite green, crystal violet, brilliant green and methylene blue by micro-cloud-point extraction and nonlinear laser wave-mixing detection interfaced to micellar capillary electrophoresis
A laser wave-mixing CE detection method is reported for separation and detection of malachite green (MG), crystal violet (CV), brilliant green (BG), methylene blue (MB), and the leuco-metabolites of MG and CV residues in aquacultures. This method applies a non-ionic surfactant for micro-cloud-point extraction (MCPE) followed by non-aqueous micellar capillary electrophoresis (MCE) for separation and nonlinear laser wave-mixing detection. The log–log plot of the MCE wave-mixing intensity vs. analyte concentration showed a good quadratic dependence with correlation coefficients greater than 0.989. The mass detection limits at an S/N of 2 were determined to be 2.27, 1.50, 23.8, 190, 27.61 and 22.2 attograms for MG, CV, BG, MB, leuco-MG, and leuco-CV, respectively. The concentration limits of detection (LODs) at an S/N of 2 were determined to be 4.13, 2.72, 10.2, 81.6, 50.2 and 40.3 pg mL−1 for MG, CV, BG, MB, leuco-MG and leuco-CV, respectively. The intra-day variability (RSD) for the retention times ranges from 0.6 to 1.0% and the average inter-day variability (RSD) ranges from 0.7 to 4.7%. This method is simple, rapid and reliable, and it allows separation and simultaneous detection of MG, CV, MB, BG, and the leuco-metabolites of MG and CV in aquatic environments.