A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was established for the determination of nonylphenol in milk powder. Samples were extracted with acetonitrile and cleaned up with a solid phase extraction column. The analytes were separated on a Waters ACQUITY UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm), detected by electrospray ionization in the multiple reaction monitoring (MRM) mode, and quantified by an external standard method. The results showed that good linearity was observed in the concentration range of 1–200 ng/mL (R2 > 0.99). The limit of detection（LOD, RS/N = 3）was 2 μg/kg and the limit of quantitation (LOQ, RS/N = 10）was 5 μg/kg. The recoveries at different spiked levels were between 81.10% and 107.39% with relative standard deviation (RSD) ranging from 1.97% to 9.73%. This method has the advantages of accurate results, small background interference, simple operation, good stability and short pretreatment time, and is useful for the detection of nonylphenol in milk powder.

A high performance liquid chromatographic (HPLC) method was developed for the determination of naringin in milk and dairy products. Samples were extracted with methanol, and the analytes were separated on a C18 column using a mobile phase consisting of 0.1% acetic acid aqueous solution and acetonitrile (75:25, V/V), detected by a diode array detector at 284 nm and quantified by an external standard method. The results showed that the linearity of this method was good in the concentration range of 5–500 μg/mL with a correlation coefficient of 0.999 9. The recoveries of powdered and liquid milk power and yogurt spiked at 0.02, 0.04, and 0.08 g/100 g were 96.2%–103.2%, 96.3%–103.7%, and 99.7%–104.1%, respectively, with relative standard deviations (n = 6) of 1.12%–2.31%, 1.25%–1.85%, and 1.24%–1.66%, respectively. The reported method is simple, rapid, accurate, repeatable, and suitable for the determination of naringin in milk and dairy products.

A method based on quick, easy, cheap, effective, rugged, safe (QuEChERS) extraction combined with gas chromatography-tandem mass spectrometry (GC-MS/MS) for the simultaneous quantitative determination of 12 organophosphorus and carbamate pesticide residues in soy milk. The samples were extracted with acetonitrile, then the supernatant was separated after addition of citrate buffer, followed by cleanup with a mixture of anhydrous magnesium sulfate, primary secondary amine (PSA) and C18 sorbents. The analytes were detected by GC-MS/MS. The results showed that the limits of quantification (LOQs) were 0.004 mg/kg for the 12 pesticides. The calibration curves were linear in the concentration range of 5–200 ng/mL with correlation coefficient greater than 0.99. The recoveries varied from 71.8% to 114.9% with relative standard deviation (RSD) from 4.6% to 13.3% at three different spiked levels. The method was found to be quick, efficient, accurate and suitable for the determination of organophosphorus and carbamate pesticide residues in soy milk.

The detection of pesticide residues in dairy products is an important measure to ensure the quality and safety of dairy products. Currently, QuEChERS (quick, easy, cheap, effective, rugged, safe) is widely used as a sample pretreatment for all existing methods specified in the national standards for the detection of pesticide residues in dairy products. In this paper, we review these methods with a special focus on the principle and advantages of QuEChERS as well as its application in the detection of pesticide residues in dairy products.

By analyzing some factors involved in the determination of lead in milk powder by inductively coupled plasma mass spectrometry (ICP-MS) such as containers and reagents used, an ultrasonic cleaning method was established to effectively reduce the blank value. The method gave a detection limit of 0.005 mg/kg, which was much lower than that (0.02 mg/kg) of traditional methods. The recoveries of samples spiked at concentration levels of 0.005–0.015 mg/kg ranged from 86.9% to 119.0% with relative standard deviations (RSDs) of 3.1%–12.3%, meeting the requirements for methodological validation. Hence, the method proved to be overall feasible and suitable for the detection of lead in milk powder with reduced detection limit.

This paper summarizes and compares the maximum residue limits for pyrethroid pesticides in milk products in China and several other countries. At the same time, the main factors affecting the accuracy of the determination of pyrethroid pesticide residues in dairy products, including calibration curve fitting and experimental repeatability, are determined through calculation of the measurement uncertainty. Furthermore, it can be argued that the most fundamental influencing factor is the sample pretreatment method.

An ultra performance liquid chromatography-tandem mass spectrometry method for the simultaneous quantitative determination of four tetracycline residues in dairy products, including milk, yogurt and milk powder, has been established. In this method, the pretreatment and instrument operating conditions were optimized. Tetracycline residues were extracted into EDTA-Mcllvaine buffer and then cleaned up by an HLB solid-phase extraction cartridge. After the residues were eluted with a mixture of methanol and acetonitrile (1:9, V/V), the eluate was blown to dryness under nitrogen. The resulting residue was then redissolved. The analysis was carried out using positive ion electrospray ionization under the multiple reaction monitoring mode. The limits of quantification were 10 μg/kg for tetracycline, oxytetracycline, chlortetracycline and doxycycline in milk powder; the limits of quantification were 2 μg/kg in milk and yogurt. The recoveries of the tetracyclines fortified at levels from 2 to 100 μg/kg ranged from 63.1% to 100.6% with relative standard deviation of 1.8%–10.7%, and the matrix effects were 100.5%–122.1%. In conclusion, this method is accurate, rapid and highly sensitive and exhibits good repeatability and wide linearity. Thus it is suitable for the determination of tetracycline antibiotic residues in milk, yogurt and milk powder.

A method for the determination of nonylphenol in liquid milk by using ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed. Samples were extracted using acetonitrile as extraction solvent and the organic phase was separated from the aqueous phase by adding saturated sodium chloride solution. The analyte was cleaned up using a ProElut PAEs Glass solid-phase extraction catridge and then separated on a Waters ACQUITY UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) using gradient elution with 0.1% ammonia water-methanol as mobile phase. The detection was performed by negative electrospray ionization under the multiple reaction monitoring mode and the quantitation was carried out by an internal standard method. The results showed a good linear relationship (R2 > 0.990) in then range from 1 to 200 ng/mL. The limit of detection（LOD, RS/N = 3）was 2.0 μg/kg and the limit of quantitation (LOQ, RS/N = 10）was 5 μg/kg. The recovery rate of the method for spiked samples was between 74.8% and 111.5% with relative standard deviation of 3.3%-9.0%. In general, the method was accurate, simple and reproducible and exhibited low background inference and it was thus suitable for the analysis of nonylphenol in liquid milk.