Analysis of impurity elements in high purity cobalt powder by inductively coupled plasma tandem mass spectrometry

An analytical method for the determination of 26 impurity elements in high purity cobalt powder was established by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). The high purity cobalt powder was disposed by microwave digestion using a mixture of nitric acid and hydrochloric acid as the digestion reagent and then determined directly by ICP-MS/MS. In the MS/MS mode, the mass spectral interferences on the analytes by polyatomic ions could be eliminated by adding different reaction gases into the collision/reaction cell (CRC). Using O2 as the reaction gas, the mass-shift reaction of P+, S+, V+, As+, Se+ with O2 occurred, and the corresponding oxide ions generated were used for the measurement. When H2 was added to the CRC as the reaction gas, the mass-shift reaction between the interfering ions and H2 occurred. Si+ and Ca+ were determined by on-mass method. When NH3/He was added as the reaction gas, cluster ions generated by the mass-shift reaction of Ti+, Cr+, Mn+, Fe+, Ni+, Cu+, and Zn+ with NH3/He. The mass-shift method was used for determination by employing the mass-shift reaction between interfering ions and NH3/He, and Na+, Mg+, A1+, and K+ were determined by the on-mass method. The matrix effect was corrected via on-line addition of the internal standard elements. The results showed that the detection limit of analyte was in the range 0.02-97.5 ng/L, and the linear correlation coefficients were ≥0.9996, showing a good linear relationship. Moreover, the spike recoveries were in the range 91.6%-109.2%. Therefore, this method is well suited for the determination of 26 impurity elements in high purity cobalt powder above 5 N (≥99.999%).