In this study, we aimed to establish a method for the determination of six pesticide residues in milk by quick, easy, cheap, effective, rugged, safe (QuEChERS) extraction combined with ultra high performance liquid chromatography-tandem mass spectrometry. Milk samples were extracted with acetonitrile, purified by the QuEChERS approach, and the extract was then blown down to dryness using a stream of nitrogen gas and re-dissolved. The liquid chromatographic separation was achieved by gradient elution using a mobile phase consisting of acetonitrile and 0.1% formic acid in water. The analysis was carried out using positive ion electrospray ionization under the multiple reaction monitoring mode. The external standard method was used for quantification. Excellent linearities were achieved for all target analytes in the range of 1.0–40.0 μg/L with correlation coefficients greater than 0.995. The limit of detection was 0.1 μg/kg, and the limit of quantification was 1.0 μg/kg. The average recoveries of the six pesticide residues from blank milk samples at three spiked concentration levels of 1.0, 2.5 and 5.0 μg/kg ranged from 76.5% to 113.7% with relative standard deviations (RSDs) of 1.5%–6.1%. The proposed method was simple, accurate, efficient and suitable for the rapid screening and quantitative analysis of pesticide residues in milk.

In this paper, an ion chromatography method for the determination of galactooligosaccharides (GOS) in milk powder was established. The protein in the sample was precipitated by acetonitrile, and GOS was extracted with acetonitrilewater and purified using a C18 column (or RP column) to remove impurities. The analyte was separated using an ion chromatograph equipped with quaternary gradient pumps and detected with a pulse amperometric detector. The calibration curve of this method had good linearity in the range of 10–300 μg/mL, and the results from repeated sample measurements were stable. The recovery rates from blank samples spiked at levels of 500–2 000 mg/100 g were 82.1%–98.0%. To sum up, this method required simple sample pretreatment and gave accurate results, and it could be suitable for the determination of the GOS content in milk powder samples.