[Determination of 19 chlorophenols in fish by QuEChERS-gas chromatography-mass spectrometry]

With the increasing use of chlorine-containing pesticides, hypochlorous acid disinfection water as well as aquatic product insecticides and fungicides are widely used in the cultivation of fish. This has led to the contamination of fish by chlorophenol compounds. However, currently, there is no standard method for the simultaneous determination of 19 chlorophenol compounds in fish. In this study, the optimum chromatography and mass spectrometry conditions were determined by investigating the instrument parameters. The 19 chlorophenol compounds were well separated using the DB-5MS capillary chromatographic column (30 m×0.25 mm×0.25 μm) with a carrier gas flow rate of 1 mL/min. Under this condition, the chromatographic peak was sharp and symmetric. An analytical method was developed for the simultaneous determination of the 19 chlorophenol compounds in fish using gas chromatography-mass spectrometry coupled with QuEChERS pretreatment. The improved QuEChERS method was used in sample preparation. The 19 chlorophenol compounds were extracted with organic solvents and purified with purifying agents. During the experiment, the effect of the kinds and volumes of the extraction solvent, as well as the types and dosages of the purifying agent, on the recoveries of the 19 chlorophenol compounds were investigated. Moreover, the temperature and time of derivatization, as well as the dosage of the derivatization agent, were optimized. All aforementioned analyses were conducted with the aim of determining the optimal pretreatment method. Finally, the optimized gas chromatography-mass spectrometry conditions were employed for the quantitative determination of 19 chlorophenol compounds in fish samples. Based on the experimental results, the best extraction method was determined to be the one where the extraction agent (10 mL ethyl acetate) was added to 3 g sodium chloride and 5 g anhydrous magnesium sulfate in the test tube, followed by ultrasonication for 15 min. The sample was centrifuged at 4500 r/min for 5 min, and 500 mg C₁₈ was selected as the purifying agent to purify the supernatant. The purified supernatant was blown with nitrogen to less than 1 mL at 45 ℃, and then redissolved with ethyl acetate to 1 mL. Subsequently, the sample solution was passed through a 0.22 μm organic filter membrane, following which 50 μL bis(trimethylsilyl)trifluoroacetamide was added for derivatization at 45 ℃ for 30 min. Lastly, the 19 chlorophenol compounds were determined by gas chromatography-mass spectrometry with an electrospray ionization source and selecting ion monitoring mode. The 19 chlorophenol compounds were then quantitatively analyzed by the external standard method. The compounds showed good linearity in the concentration range of 0.4-10 μg/L, with correlation coefficients (R²) greater than 0.998. The limits of detection and limits of quantification were 0.01-0.05 μg/kg and 0.04-0.16 μg/kg, respectively. Moreover, the average recoveries of the 19 chlorophenol compounds were in the range of 70.6%-115.0% at three spiked levels, and the relative standard deviations were in the range of 2.6%-10.5%. The established method in this study was applied to detect and analyze chlorophenol compounds in actual samples. The experimental results showed that various levels of chlorophenol compounds could be detected in different fishes. Among them, the total amount of chlorophenol compounds detected in the Corvina was 8.74 μg/kg, followed by the Crucian carp at 7.59 μg/kg, and the minimum detected amount in rice fish (1.59 μg/kg). With its simple operation, high sensitivity, and good repeatability, the established method simplifies the pre-treatment of fish samples. It can also meet the requirements for the high-throughput detection of 19 chlorophenol compounds in fish, thereby significantly improving the detection efficiency of chlorophenols. Moreover, the method provides crucial technical support and a theoretical basis for the establishment of feasible detection standards for chlorophenols in China, as well as for the control of residue levels of chlorophenol compounds in fish. The findings have important practical significance to implement management measures during fish breeding and transportation.