An analytical method for the determination of 4 steroid hormones in milk and milk power was developed by filtration solid phase extraction combined with ultra performance liquid chromatography-tandem mass spectrometry. Samples were extracted with acetonitrile, and purified on a PRiME HLB cartridge. Then the chromatographic separation was achieved using an Acquity BEH C18 column (2.1 mm × 100 mm, 2.5 μm) with a mobile phase consisting of water and acetonitrile. The compounds were ionized using an electrospray ionization source in the negative ion mode and quantitated by the internal standard method. The results showed that the calibration curves of all analytes had a good linear relationship in the concentration range of 0.2–100.0 ng/mL. The limits of detection and limits of quantitation were 0.4–2.0 and 0.8–4.0 μg/kg, respectively. The recoveries of the method were in range of 87.7%–110.8% with relative standard deviations (RSDs) of 0.85%–4.56% in milk and in range of 89.2%–107.4% with RSDs of 0.85%–4.56% in milk power. This method was proved to be rapid, sensitive, and useful for the quantification of 4 steroid hormones in milk and milk power samples.

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the determination of vancomycin, norvancomycin and teicoplanin in milk samples. Selective reaction monitoring was performed and the external standard method was used for quantification. Among various solvents tested, 0.1% formic acid-acetonitrile (85:15, V/V) was selected. Samples were ultrasonically extracted and vancomycin and norvancomycin were cleaned up by cation exchange column chromatography, while teicoplanin was purified using a C18 solid-phase extraction (SPE) cartridge. Acetonitrile-0.1% formic acid solution was chosen as mobile phase for gradient elution. The analytes were separated on a reversed-phase C18 column before being analyzed by mass spectrometry. The limits of detection (LOD) for vancomycin, norvancomycin and teicoplanin were 2, 1 and 2 μg/kg, and the limits of quantitation (LOQ) were 4, 2 and 4 μg/kg, respectively. The recoveries of the method ranged from 77.3% to 84.5% at spiked levels equal to LOQ, 5 × LOQ and 10 × LOQ, with relative standard deviations (RSD) of 4.7%–7.2%. The method could be used in the qualitative and quantitative detection of vancomycin, norvancomycin and teicoplanin in milk samples.

An efficient method was developed for the simultaneous analysis of six estrogens including diethylstilbestrol, α-estradiol, β-estradiol, estriol, estrone and bisphenol A in milk powder using gas chromatography-tandem mass spectrometry (GC-MS-MS). Samples were enzymatically hydrolyzed and extracted with acetonitrile. The extract was then derivatized with pentafluoropropionic anhydride before being injected into the GC-MS-MS system. Qualitative and Quantitative analysis was carried out under the multiple reaction monitoring (MRM) mode. The results indicated that all six estrogens displayed a good linear relationship with R2 ＞ 0.999. The limits of quantification for bisphenol A and the other five estrogens were 0.03 and 0.3 μg/kg, respectively. The average recovery of six estrogens was 93.93%, with RSD of 6.05%, meeting the methodological requirements. The method developed in this study can be successfully applied in the determination of six estrogens in milk powder.