Determination and Confirmation of Leucomalachite Green in Salmon using No-Discharge Atmospheric Pressure Chemical Ionization LC-MSn

An LC-MS method utilizing no-discharge atmospheric pressure chemical ionization (APCI), in conjunction with an ion trap instrument to generate product ion spectra, was developed to quantitate and confirm residues of leucomalachite green (LMG) in salmon tissue after conversion to the chromic malachite green (MG) in the extraction process. For the most efficient use of laboratory resources, the same extracts prepared for an LC-VIS method can be used for LC-MS analysis. The sample preparation procedure involves extraction of tissue into acetonitrile/buffer, partition of LMG residue into methylene chloride, conversion of LMG to MG using an organic oxidizing agent, followed by the isolation of MG on alumina/propyl sulfonic solid phase extraction cartridges. The validation of this method was performed by fortifying salmon with different levels of LMG, and then detecting the residue as MG. LC-MS conditions, including a comparison of electrospray and no-discharge atmospheric pressure chemical ionization (APCI), were evaluated and optimized. Confirmation criteria for retention time and product ion relative abundances that need to be met for positive identification o