Determination of eight organophosphate esters in animal-derived foods by ultra performance liquid chromatography-tandem mass spectrometry

Organophosphate esters (OPEs) are widely used as flame retardants in most regions, they adversely affect ecosystems and threaten human health. OPEs have attracted significant public attention because they are toxic and ubiquitously present in the environment. While China is among the world's largest users and producers of OPEs, limited data on the exposure of animal-derived foods to OPEs exist; consequently, a method for quantifying OPEs in animal-derived food samples is needed. In this study, a method was developed for the determination of eight OPEs, including triethyl phosphate (TEP), tripropyl phosphate (TPrP), tri-<i>n</i>-butyl phosphate (TnBP), tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), triphenyl phosphate (TPHP), and 2,2-bis(chloromethyl) trimethylene bis[bis(2-chloroethyl) phosphate] (V6), from twelve types of typical animal-derived foods by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were purified using an HMR-Lipid SPE column. The effects of mobile phase A (water, 5 mmoL/L ammonium acetate aqueous solution, and 0.1% formic acid aqueous solution) and mobile phase B (methanol and acetonitrile), as well as the methanol/acetonitrile ratio on the separation and extraction efficiencies for the eight OPEs were investigated using one-way analysis. The results showed that optimal response values and peak shapes were obtained for the various compounds using 0.1% formic acid aqueous solution-acetonitrile system as the mobile phase. The following pretreatment procedure was used: A 0.5 g sample was accurately weighed and ultrasonically extracted with 5 mL of acetonitrile. The supernatant was collected after freezing and centrifugation, and cleaned-up was performed using an HMR-Lipid SPE column. The target analytes were analyzed using a Waters Acquity BEH C₁₈ column (100 mm×2.1 mm, 1.7 μm) and ESI⁺ MS conditions. Compound V6 was quantified by the external standard method, with the other seven compounds quantified using the internal standard method. The method exhibited linearity with <i>r</i>²≥0.9900, limits of detection (LODs) of 0.01-0.87 μg/kg, and limits of quantification (LOQs) of 0.02-2.62 μg/kg for the various substances. Spiked recoveries of the eight OPEs at three levels (2, 20, and 100 μg/kg) were in the range of 80.5%-117.8% and RSDs ≤ 14.8% (<i>n</i>=6). Twelve animal-derived foods (grass carp, bass, <i>Procambarus clarkii</i>, milk, milk powder, yogurt, pork, beef, chicken, duck meet, egg, and duck egg) were analyzed using the developed method. Compounds TnBP and TCIPP were detected at rates of 100%, and TEP, TCEP, TPHP, and TDCIPP at rates greater than 50%, while TPrP and V6 were not detected. The method has a simple-to-operate pre-treatment step, analyzes rapidly with good recoveries and precisions, and is suitable for rapidly analyzing and detecting eight OPEs in a variety of animal-derived foods.