Simultaneous determination of 128 pesticide residues in milk by liquid chromatography-tandem electrospray mass spectrometry

A method has been developed for the simultaneous determination of 128 pesticide residues in milk by liquid chromatography-tandem electrospray mass spectrometry (LC-ESIMS/MS). A total of 10 mL milk was extracted with 20 mL acetonitrile (plus 4 g magnesium sulfate and 1 g NaCl) for two times. The concentrated supernatant was cleaned-up by a C-18, solid phase extraction cartridge to remove the lipophilic compounds. The eluate was concentrated to about 0.5 mL in 45 degrees C water bath with nitrogen. The 1 mL mixture of acetonitrile and water (3: 2, v/v) was added into the sample and mixed thoroughly for 30 s. The sample solution was filtered by 0. 2 mu m millipore filters before LC-ESI-MS/MS determination. This method was evaluated at the two spiked levels of 2 times and 8 times of limits of the detection (LODs) in 5 parallel experiments, respectively. The results showed that the average spiked recoveries of 128 pesticides at the low spiked level (0. 14 mu g/L- 0. 62 mg/L) were from 60. 4% to 118.4% with relative standard deviations (RSDs) of 2. 1% - 24. 3%, and the average spiked recoveries at the high spiked level (0. 56 mu g/L- 2. 48 mg/L) were from 64. 4% to 118. 5% with the RSDs of 1. 3% - 24. 1%. The method showed a good linear relationship with the correlation coefficients over 0. 99. The LODs were from 0. 07 mu g/L to 0. 31 mg/L. This method is selective, accurate and easy to operate.