Determination of malachite green and leucomalachite green residues in water using liquid chromatography with visible and fluorescence detection and confirmation by tandem mass spectrometry.

A liquid chromatography with visible and fluorescence detection (LC-vis/FLD) method for screening and a liquid chromatography with mass spectrometry (LC-MS/MS) method for the confirmation of malachite green (MG) and its major metabolite, leucomalachite green (LMG) residues in water have been described. Water samples were preconcentrated on diol solid-phase extraction columns. Chromatographic separation was achieved by using phenyl-hexyl column with an isocratic mobile phase consisting of acetonitrile and acetate buffer (0.05M, pH 4.5) (70:30, v/v). In screening method liquid chromatography with absorbance detector was used for the detection of MG while LMG was detected by fluorescence detector. Detectors were connected on-line that allowed direct analysis of a sample extract for MG and LMG without the need of any post-column procedure. For the confirmation of MG and LMG in water positive electrospray ionization mass spectrometry in the multiple reaction monitoring mode was used. The developed methods have been validated according to the European Union requirements (Commission Decision 2002/657/EC). For LC-vis/FLD the mean recoveries at three fortification levels (0.4, 1, and 2microgl(-1)) were in the range 95.4-104.7% for MG and 62.2-81.9% for LMG, whereas for LC-MS/MS, recoveries of MG and LMG were in the range 96.9-101.3% and 97.5-104.0%, respectively. Relative standard deviations of recoveries for both methods were less than 3.8 and 8.1% for MG and LMG, respectively. The stability of MG and LMG at 4 degrees C in darkness was observed for at least 10 months. Moreover, photo-oxidative decomposition products of analytes in water samples, observed in stability tests carried out at 20 degrees C, were identified by mass spectrometry as N-demethylated products of MG and LMG. These findings prove that N-demethylated products of MG and LMG, reported as potential carcinogens, may be formed in living fish organisms not only during enzymatic action but also during photo-oxidative degradation in water.