QuEChERS-based purification method coupled to ultrahigh performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) to determine six quaternary ammonium compounds (QACs) in dairy products

• A UPLC–MS/MS method was established for 6 QACs determination in dairy products.
• QuEChERS purification technology, acetonitrile vortex extraction method were used.
• Stable isotope internal standard method was adopted in quantification.
• The complex dairy products samples can be favorably purified by the pretreatment.
• Satisfactory linearity, recoveries, accuracy and precision were obtained.

QuEChERS-based purification coupled with UPLC–MS/MS method, was developed for six quaternary ammonium compounds (QACs) determination in dairy products. Powder samples were firstly dispersed by water. Protein in liquid milk was precipitated and sample solution was extracted by acetonitrile. QuEChERS-based purification was used to purify the solution. QACs were finally separated by HILIC column and detected in MRM mode of MS/MS under ESI+. The stable isotope benzyl-2,3,4,5,6-d5-dimethyltetradecylammonium bromide (C14-BAC-d5) was used as an internal standard. This method was validated in terms of linearity, sensitivity, precision, accuracy. Linear relations were favorable for QACs over the selected concentration ranges of 0.2–50 μg/L, with correlation coefficients greater than 0.999. The limits of detection (LODs) were in the range of 0.4–14.5 μg/kg. Recoveries were between 91.2% and 115% with RSDs of 2.8–7.5% for intra-day precision and 3.7–6.7% for inter-day precision. This validated method was successfully applied to determine the QACs concentrations in dairy products.