An inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) method was established for the analysis of 26 inorganic elements in dairy products. Under MS/MS conditions, the 26 elements were detected in the no gas, collision gas (He) or reaction gas (H2, O2, NH3/He) mode and the optimal mode was selected for each of the elements. The results showed that calibration curve with good linearity was obtained for each element in the appropriate detection mode with a correlation coefficient greater than 0.999 0. The detection limits of the 26 inorganic elements ranged from 0.000 033 61 to 0.043 71 mg/kg. The spiked recoveries were between 95.50% and 104.21%, with a relative standard deviation (RSD) ≤ 3.94% (n = 11). The contents of Na, Mg, K, Ca, P, Fe and Zn were higher and the contents of the heavy metal elements Cr, As, Cd and Pb were lower in six kinds of dairy products, all of which were lower than the national standard limits. The method was characterized by simple pretreatment, high sensitivity, low limit of detection and high accuracy and could be used for the detection of inorganic elements in dairy products.

In this paper, Cr (Ⅲ) and Cr (Ⅵ) in milk were determined by high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). A PRP-X100 cation exchange column was used. The influence of mobile phase concentration, pH value and flow rate on the degree of separation and retention time was investigated. The mobile phase selected was NH4NO3solution (0.10 mol/L, pH 7) at a flow rate of 1.0 mL/min. Under the optimized conditions, the mass spectrometric and ion interferences were eliminated by using the natural abundance ratio of 52Cr to 53Cr as reference value, and the retention time of Cr (Ⅲ) and Cr (Ⅵ) were determined to be 2.227 and 1.856 min, respectively. Good linearity was observed for Cr (Ⅲ) and Cr (Ⅵ) with correlation coefficients of 0.999 5 and 0.999 7, respectively. The detection limits were 0.015 and 0.016 μg/L, respectively. The overall recoveries for the two valence states were in range of 71.52% to 90.27%. This method proved to be useful for simultaneous analysis of different Cr valence states in milk and dairy products.