Quantification of Trace Elements in Superalloy by Quadrupole ICP-MS Based on Oxygen Reaction Mode and Study on the Elimination Mechanism of Spectral Interference

A method of quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) based on oxygen reaction mode was established for the accurate determination of trace impurity elements in superalloys. The effect of the collision/reaction mode on the removal of mass spectral interference was investigated. By contrast, the polyatomic mass spectral interference on the target element Cd can be effectively removed under oxygen dynamic reaction cell (DRC-O₂) mode. The signal-to-noise ratio (SNR) peaked when the gas flow was 2 mL/min, and the detection limit was approximately three orders of magnitude lower than that under standard (STD) mode. In addition, the elimination mechanism of mass spectrometric interference was studied. It was found that for the element X (X=Rb, Nb, Mo, Cs, Ta, W or U), the conversion of the interferent species XO to the non-interferent species XOO is a spontaneous reaction when the bond energy of X−O bond is higher than that of O−O bond. Therefore, it is easier to generate ions of XOO species when there is adequate O₂ present in the ion source, so as to eliminate XO interference. Based on these results, experiments were carried out to determine elements of Rb, Nb, Mo, Cs, Ta, W and U. The matrix simulated solutions containing high concentration of Mo, Nb, Ta, and W were used to evaluate the methodological parameters for the measurement of trace Cd, Ag, Au, and Hg impurities, respectively. The limit of detection (LOD) of the trance elements is 0.08-0.31 μg/g, the relative standard deviation (RSD) of the measurement is 2.3%-3.1% (n=6), and the spiked recovery is in the range of 98%-103%. The reliability of the method was further verified by certified superalloy reference materials. Finally, the trace impurities in three types of superalloy samples were measured. The results indicated that the proposed method can achieve rapid, reliable analysis with low detection limit. Besides, it can meet the measurement requirement of trace impurities when the main elements of Mo, Nb, Ta and W exist in superalloy.