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.

Inductively coupled plasma emission spectrometry (ICP-OES) was used to determine the contents of 12 trace elements (K, Na, Ca, Mg, Fe, Zn, Cu, Mn, P, Sr, Al, and Cr) in premixed feed and crude feed for dairy cows. Samples were pretreated with microwave digestion before being analyzed. The calibration curves of all elements were linear with correlation coefficients above 0.999 8. The spiked recoveries for this method were 90.0%–106.9%, and the coefficients of variance (CV) for six replicate determinations were 0.69%–8.70%. With the advantages of low limits of detection and high sensitivity and accuracy, this method could be useful for the simultaneous determination of multiple trace elements in dairy feeds.

A method for the determination of lactose in low-lactose milk and lactose-free milk by using ion chromatography was developed. Lactose from samples was extracted with 3% acetic acid as a protein precipitator. The method was performed on a CarboPacTM PA20 column by gradient elution. The analyte was detected with an electrochemical detector and quantified by an external standard method. The limit of quantification was 100 mg/kg and the limit of detection was 50 mg/kg for lactose in milk. The recoveries at spiked concentration levels of 100–500 mg/kg were 92.3%–103.4%, with relative standard deviations between 1.44% and 4.43%. This method proved to be rapid, accurate, repeatable, sensitive and simple.

An ultra performance liquid chromatography-tandem mass spectrometry method for the simultaneous quantitative determination of four cephalosporin residues in dairy products, including milk, yogurt and milk powder, has been established. The samples were extracted with 5% formic acid acetonitrile. After being purified by solid-phase microextraction using an Oasis PRIME HLB cartridge, the extract was blown to dryness under a stream of nitrogen gas and then re-dissolved. The analysis was carried out using a positive electrospray ion source in the multiple reaction monitoring mode. The limit of quantification was 32 μg/kg for cefalexin, cefapirin, cefalonium and cefquinome?in milk powder; the limit of quantification was 4 μg/kg in milk and yogurt. The recoveries at spiked concentration levels of 4-150 μg/kg were 63.3%-112.1%, with relative standard deviations of 1.6%-10.5%. The matrix effects were 108.77%-379.91%. This method was characterized by short analysis time and was suitable for the determination of cephalosporin residues in different dairy products.

A gas chromatography-mass spectrometry (GC-MS) method was developed for determining β-sitosterol in milk by optimizing important sample pretreatment parameters such as saponification temperature, extraction solvent, extraction number, shaking method during extraction and rotary evaporation temperature. The feasibility of the developed method was examined. This method exhibited a wide linear range and could meet the requirements for routine quantitative analysis of β-sitosterol in milk samples with high precision, good repeatability, accurate results and high reliability.

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.