Capillary electrophoresis combined with accelerated solvent extraction as an improved methodology for effective separation and simultaneous determination of malachite green, crystal violet and their leuco-metabolites in aquatic products
Malachite green (MG), crystal violet (CV) and their leuco-metabolites (LMG, LCV) could not be determined simultaneously by capillary zone electrophoresis because of their similar structures, low solubility in water, and easy degradation/de-methylation. A novel capillary electrophoresis (CE) method with UV detection for the effective separation and simultaneous determination of the four compounds was developed for the first time. The use of an acetonitrile–sodium dodecyl sulfate (SDS)–ammonium acetate buffer solution (pH 4.0) achieved the effective separation of the four compounds. The effects of CE conditions on separation were investigated in detail. Accelerated solvent extraction (ASE) with acetonitrile as an extractant in the presence of hydroxylamine hydrochloride and p-toluenesulfonic acid was used to extract the four compounds in aquatic products with high extraction efficiency. Under optimized separation conditions, the four analytes could be baseline separated, and there was no interference in analysis of real samples. Calibration curves have good linearity with a correlation coefficient (r) greater than 0.999. The limit of detection for MG, CV, LMG, and LCV were 0.39, 0.29, 0.08, and 0.10 μg mL−1, respectively. The intra- and inter-day variability (RSD) of peak areas were in the range of 0.3–3.4% and 1.0–4.7%, respectively. Average recoveries were 92.6–107% with RSD of 2.1% for shrimp samples, 95.4–108% with RSD of 2.3% for eel samples, and 89.1–105% with RSD of 3.1% for sardine samples. The proposed ASE–CE method has the advantages of high selectivity, good linearity and precision.