Determination of low concentrations of organochlorine pesticides and PCBs in fish feed and fish tissues from aquaculture activities by gas chromatography with tandem mass spectrometry

A sensitive and rapid multiresidual method has been developed for the determination of organochlorine compounds in fish feed and fish tissues. The method is based on automated off-line normal-phase liquid chromatography (NPLC) clean-up prior to GC-MS/MS. Analytes are extracted by refluxing in n-hexane and fats present in the hexanic extracts are removed by automated NPLC, using n-hexane and ethyl acetate as mobile phase. Both NPLC and acid digestion with sulphuric acid have been evaluated as clean-up techniques for the analysis of these kinds of fatty samples. Thus, acid digestion is recommended before NPLC when large amounts of fat are present in the extracts. Purified extracts are then analysed by GC-MS/MS (electron impact, El) using the extracted ion mode. The high efficiency of elimination of fats from the extracts together with optimised MS/MS detection leads to high sensitivity in the multiresidue determination of analytes, reaching limits of detection at the sub-ppb level in this type of fatty samples (up to 19% lipids fresh weight). The developed procedure represents an improvement over current methodologies for the analysis of organochlorine compounds (M) in fatty samples as regards to solvent consumption and automation, allowing the application of automated off-line NPLC (26 min per sample) prior to GC determination. Besides, changes of solvent are not necessary during analysis. The application of the developed procedure to real world samples of fish feed and cultured fish revealed the presence of HCB, DDTs, and PCBs at ng g(-1) levels.