Abstract: In this study, an analytical method was established to determine pentachlorophenol (PCP) in milk powder by isotope dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS). The sample was dissolved in water, extracted by the quick, effective, cheap, easy, rugged and safe (QuEChERS) method using acetonitrile as the extraction solvent and protein precipitant, purified on a Captiva EMR-Lipid column, and diluted with the same volume of water before analysis. The chromatographic separation was achieved on a C18 column (100 mm × 2.1 mm, 1.7 μm) with gradient elution using a mobile phase composed of methanol and 5 mmol/L ammonium acetate solution (containing 0.05% formic acid), and then the analyte was detected with negative electrospray ionization (ESI-) in the multiple reaction monitoring (MRM) mode. Matrix matching-isotope dilution internal standard method was used for identification and quantification of the analyte. The results indicated that the calibration curve of PCP was linear in the concentration range of 0.2‒150 μg/L with correlation coefficients (r) not less than 0.996 0. The limits of detection (LOD) and quantitation (LOQ) of the method were 0.5 and 1.5 μg/kg, respectively. The average recoveries for spiked milk powder ranged from 90.3% to 119.2%, with relative standard deviation (RSD, n = 6) equal to or less than 7.5%. The method has the advantages of simple pretreatment without concentration or dissolution, high sensitivity, accuracy and reliability, and can be used as an effective method for detecting pentachlorophenol in milk powder.

Key words: isotope dilution; liquid chromatography-tandem mass spectrometry; milk powder; pentachlorophenol