Relative Matrix Effect in the Quantification of Nitroimidazoles and Dyes in Meat, Eggs, Shrimp, and Fish Using an Ethyl Acetate/Salting-Out Extraction and Isotope Dilution Ultra-High Performance Liquid Chromatography–Tandem Mass Spectrometry

This paper presents the validation of a multiresidue method for quantifying seven nitroimidazoles and four dyes in poultry, pork, beef, eggs, shrimp, and fish. The average matrix factors of standard normalized to IS (0.82-1.12) indicated no significant matrix effect, and the CV % values (2.26-12.10%) complied with the 20% limit of the Commission Implementing Regulation 2021/808. However, medium suppression (50-80%) or enhancement (120-150%) was observed in 4.29% and 2.14% of the individual matrix extracts, respectively. The linearity ranges (in μg kg^-1) were 0.50-3.0 for nitroimidazoles and 0.25-1.5 for dyes, and the determination coefficients (<i>R</i>²) were at least 0.9688. The limits of quantitation were the lowest calibration levels. Analyte recovery and reproducibility were satisfactory (<i>f</i>_REC: 77.95-115.0%; CV: 5.09-27.24%). The decision limits (CCα) (in μg kg^-1) were 0.59-1.00 for nitroimidazoles and 0.29-0.46 for dyes and complied with the EURLs minimum method performance requirements (1.0 and 0.5 μg kg^-1, respectively).