Optimization of a modified QuEChERS method for the determination of tetracyclines in fish muscle by UHPLC-MS/MS

In this work a sample treatment based on a modified QuEChERS method combined with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was proposed to determine the residues of five common tetracyclines in fish muscle samples. The separation was achieved in less than 4 min and the analytes were detected in electrospray ionization in positive mode (ESI+) with multiple reaction monitoring mode. Parameters affecting the extraction step, such as the amount of sample and EDTA-McIlvaine buffer and extraction solvent volumes, were optimized by means of experimental design. In order to obtain the lowest matrix effect, parameters affecting the clean-up step by dispersive solid phase extraction (dSPE), were also studied. Under optimum conditions, matrix effect was lower than │15│% in all cases. Limits of quantification were lower than 4.4 μg kg^-1 for the compounds in the selected samples, being in compliance with the current legislation. The precision, expressed as relative standard deviation, was below 18.5% and the recoveries for fortified fish samples (salmon and panga) higher than 80%. These results revealed that the proposed method is simple, rapid, cheap and environmentally friendly, being successfully applicable for the determination of these residues in fish samples.