To develop a method for simultaneous determination of 10 water-soluble vitamins (nicotinic acid, nicotinamide, vitamin B2, pyridoxine, pyridoxal, pyridoxine, pantothenic acid, biotin, folic acid and vitamin B12) in infant milk by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Samples were dissolved in water, and adjusted to pH 1.7 with 5 mol/L HCl solution and then to pH 4.5 with 5 mol/L NaOH solution to precipitate proteins. The supernatant was added with a mixed solution of isotope internal standard, and separated on an ACQUITY UPLC HSS T3 column (2.1 mm × 50 mm, 1.8 μm) by gradient elution using a mobile phase composed of 10 mmol/L ammonium formate aqueous solution (containing 0.1% formic acid) and 10 mmol/L ammonium formate methanol solution (containing 0.1% formic acid). Detection was performed by electrospray ionization in the positive ion mode with multiple reaction monitoring (MRM). The external standard method was used for the quantification of pyridoxine, pyridoxal and pyridoxine, and the internal standard method for the other seven vitamins. Good linearity of the calibration curves for the 10 water-soluble vitamins was obtained in the range of 10–5 000 ng/mL with correlation coefficients (R2) above 0.99, and the recoveries for spiked samples ranged from 73.9% to 106.0%, with relative standard deviations (RSDs) of 0.9%–8.0%. The proposed method is simple, rapid, sensitive and accurate, and can meet the requirements for the determination of the 10 water-soluble vitamins in infant formula.

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.