In this paper, a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was proposed to simultaneously detect multiple pesticide residues in milk. The sample was extracted with acetonitrile, and partitioned by adding sodium chloride and magnesium sulfate. The extraction was carried out twice, and then the extract was purified with a C18 solid phase extraction column. Finally, the eluate was collected and evaporated to dryness after rotary evaporation, and the resulting residue was redissolved prior to instrumental analysis. The chromatographic separation was performed on a C18 column using gradient elution with a mobile phase consisting of 5 mmol/L ammonium acetate (containing 0.1% formic acid) and methanol. The detection was conducted using an electrospray ionization source under the multireaction monitoring (MRM) mode. The results showed that the calibration curves for acetamiprid, aldicarb, clothianidin, methamidophos, novaluron, fenbutatin-oxide, spirodiclofen, difenoconazole, cycloxydim, metaflumizone and 2-methyl- 4-chloro-phenoxyacetic acid (MCPA) had a good linearity in the concentration range of 0–100 ng/mL with correlation coefficients (R2) all greater than 0.995 0. The average recoveries for blank milk samples at three spiked concentration levels (1, 2 and 4 μg/L) were 40.2%–99.2%, with relative standard deviation (RSD) less than 18.9%, and the detection limit of the method was 1.00 μg/L. This method could allow quick and sensitive analysis of the contents of 11 pesticide residues in milk.

This study established a method for the simultaneous detection of 19 β-agonist veterinary drug residues in milk samples. The samples were extracted with acidified acetonitrile solution, and the phospholipids were removed by using an Oasis PRiME HLB solid-phase extraction cartridge. The analytes were detected by ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Under optimized pretreatment and instrumental conditions, all analytes showed a good linear relationship in the concentration range of 0 to 10 ng/mL (R2 ≥ 0.995). The average recovery rates for milk samples spiked at levels of 0.2 to 1.0 μg/kg were between 70% and 110%, and the precision relative standard deviation (RSD) was less than 15%. The method had the advantages of simple and fast pretreatment, and high sensitivity and stability, and therefore could be used for the rapid detection of β-agonist veterinary drug residues in milk.

This paper describes a method for determination of vitamin K2 (menaquinone-7, MK-7) in milk powder using high performance liquid chromatography (HPLC). The sample was hydrolyzed with lipase (250 mg/g) for 2 h, saponified with potassium carbonate (500 mg/g), extracted with n-hexane, concentrated by rotary evaporation, reconstituted with methanol/isopropanol (4:1), and post-derivatized with C18 column and reduced column before being analyzed by HPLC with a fluorescence detector. The analyte was quantified by external standard method. The results showed that the peak of MK-7 appeared at about 19.47 min, and the calibration curve for it showed a good linear relationship in the range of 0.0–1.5 μg/mL (R2 = 0.999 95). The recoveries for blank samples spiked at 5, 10 and 25 μg/100 g were between 87.9% and 94.3%, with relative standard deviations of 0.9%–6.4%. When 2 g of sample was taken and the volume was made up to 1 mL, the detection limit was 0.15 μg/100 g and the quantification limit was 0.5 μg/100 g. The method was simple with high accuracy, sensitivity and stability, and could be used for the detection of vitamin K2 (MK-7) content in milk powder.

An analytical method was developed for the determination of casein phosphopeptides (CPP) in powdered formulae for infants and young children by high performance liquid chromatography. Three pretreatment methods and two operating conditions were optimized. The results showed that the optimal pretreatment conditions were as follows: transferring samples to a 50 mL volumetric flask after pH adjustment to 4.6 with 1 mol/L hydrochloric acid, and then filtering them through a filter paper. The chromatographic separation was carried out by gradient elution using 0.05% trifluoroacetic acid as mobile phase A and 0.05% acetonitrile as mobile phase B. The spiked recovery was between 94.50% and 95.45%, good linearity was observed with R2 = 0.999 8, and the detection limit was 2.0 mg/100 g. The method had the advantages of simple sample pretreatment as well as good stability and reliability, and the results from this method met the requirements in terms of linearity, recovery, accuracy, precision and detection limit. Thus it could be used to determine the content of CPP in powdered formulae for infants and young children.

A gas chromatography-mass spectrometry (GC-MS) method was developed for the determination of quinoxyfen in milk. The sample was extracted with acetronitrile, and then the extract was cleaned up by dispersive solid-phase extraction (dSPE) with C18 and N-propyl ethylenediamine (PSA) as sorbent materials. The analyte was separate on an Agilent HP- 5MS column, detected by GC-MS, and quantified by matrix-matched external standard method. The results showed that good linearity was obtained within the concentration range of 0.00–1.00 μg/mL with a correlation coefficients (R2) > 0.998 7. The average recoveries at three spiked levels (5, 10 and 20 μg/kg) ranged from 83.2% to 100.8% with relative standard deviations (RSDs) of 2.1%–4.3%. The limit of quantitation was 5 μg/kg. The proposed method was simple, sensitive and reliable, and could be applied to the determination of quinoxyfen in milk. The content of quinoxyfen in milk samples from 75 dairy households was detected to be less than the national limit value by this method.