An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous quantitative determination of fipronil and its metabolites in whole egg powder, egg yolk powder and dairy products was developed. Samples were extracted with acetonitrile and saturated sodium chloride solution was added to separate the organic and aqueous phases. The supernatant after low-temperature precipitation of protein was applied onto an HLB solid-phase extraction cartridge for purification. The chromatographic separation was accomplished with an Acquity UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) using gradient elution with a mobile phase consisting of a mixture of acetonitrile and water. The analytes were detected using a negative electrospray ion source under the multiple reaction monitoring mode and quantitated by the external standard method. The results demonstrated that the linear ranges were from 0.5 to 20.0 μg/L with good correlation coefficients (R2 > 0.990). The limit of detection and the limit of quantitation were 0.2 and 1.0 μg/kg for all analytes, respectively. The recoveries of fipronil and its metabolites in different matrixes at spiked concentration levels of 1, 2, 4 and 20 μg/kg varied from 63.4% to 118.7%, with relative standard deviations between 0.7% and 10.3%. The method proved to besensitive, accurate and suitable for the rapid quantification of fipronil, fipronil sulfide, fipronil sulfone and fipronil desulfinyl in protein-rich foods.

An ultra performance liquid chromatography-tandem mass spectrometry method for simultaneous quantitative determination of four quaternary ammonium compounds in dairy products, including milk, yogurt and milk powder, has been established. Quaternary ammonium compounds from samples were extracted with methanol and cleaned up by solid phase extraction using a weak cationic exchange reversed-phase adsorbent (WCX). The chromatographic separation was achieved using a mixture of formic acid and methanol (2:98, V/V) as the elution solvent. The eluate was evaporated to dryness under a stream of nitrogen gas and the residue was re-dissolved prior to analysis using a positive electrospray ion source in the multiple reaction monitoring mode. The limit of quantification was 10 μg/kg for dodecyl trimethyl ammonium bromide, benzylcetyldimethyl ammonium chloride, tetradecyl dimethyl benzyl ammonium chloride and didecyl dimethyl ammonium chloride in all three dairy products. The recoveries at spiked concentration levels of 10-200 μg/kg were 81.4%-105.6%, with relative standard deviations ranging from 0.97% to 6.04%. The matrix effect was in the range of 90.89%-234.94%. This method was rapid, accurate, repeatable and was suitable for the determination of quaternary ammonium compounds in various dairy products.

A method was developed for the simultaneous determination of 2 ultraviolet absorbers UV-326, UV-1577 and 2 antioxidants AO-1010 and AO-2246 in milk by high performance liquid chromatography. Samples were extracted with acetonitrile. The effective separation of the target analytes was accomplished on Agilent HC-C8 (150 mm × 4.6 mm, 5.0 μm) column with gradient elution procedure using a mixture of water and acetonitrile as the mobile phase. External calibration was used for quantitative determination at detection wavelength of 280 nm. The linearity of 4 analytes were satisfactory with a correlation coefficient of > 0.9995 at concentrations ranging from 0.05 to 50 μg/mL. The limits of detection of the method were 0.02?0.5 mg/kg, and the recoveries at different spiked levels and precision (RSD) were 69.08%?115.87% and 0.43%?9.94%, respectively. The method is simple, sensitive, reproducible and suitable for the simultaneous determination of 2 ultraviolet absorbers and 2 antioxidants in milk.

In January 2013, it was reported that dicyandiamide (DCD) residues were detected in New Zealand milk and milk products, which has received worldwide concern. Therefore, the development of methods to detect dicyandiamide in milk and dairy products has become a hot topic. In this paper, we review methods used to detect dicyandiamide in milk and dairy products such as HPLC-MS/MS, UPLC-MS/MS and UFLC-MS/MS, including sample extraction and purification, chromatographic column selection, mobile phase composition optimization, mass spectrometry monitoring mode and matrix effect of samples.

An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) method for simultaneous determination of dicyandiamide in feed, milk and dairy products was developed. The extraction methods for feed, milk and dairy products were studied, and this was followed by selection of an appropriate chromatographic column. Samples were extracted with acetonitrile and the extract was then cleaned up on a C18 solid-phase extraction column, frozen and certrifuged to remove protein impurities, and separated on an Acquity BEH Amide column using a mobile phase composed of acetonitrile containing 0.1% formic acid and 10 mmol/L ammonium formate solution by gradient elution. Detection was performed by positive ion electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode. The proposed method had good linearity in the concentration range of 1–1 000 μg/L with correlation coefficients more than 0.995. The quantification limit for feed was the highest, 40 μg/kg. Recoveries at different spiked concentrations were 80.5%– 108.4%, with RSD less than 7.0%. This method proved to be simple, rapid and suitable for the determination of feed, milk and dairy products.

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.