Determination of Trace Au in Single Crystal Superalloys Containing Ta and Hf by ICP-MS after Complexing Separation with Ammonia

A method for the determination of trace Au in single crystal superalloys containing Ta and Hf was established by inductively coupled plasma mass spectrometry (ICP-MS) after complexing separation with ammonia. The sample was dissolved by a mixed solution of hydrochloric acid and nitric acid with a volume ratio of 3:1 at 60℃ for 30 min. To precipitate Ta and Hf and complex Au for determination, the acidity of the solution was adjusted to pH 9.0 with adding ammonia dropwise. After keeping under steady condition for 30 min, the solution was passed through filter paper. 50% (volume fraction) nitric acid solution was added and the volume of the solution was made up to 50 mL with water. The content of Au in the solution was determined by quadrupole-ICP-MS at the radio-frequency powder of 1 350 W and argon flow rate of 0.70 L·min^-1, and the standard curve was made with the matrix matching standard solution series. The results showed that when ammonia complex separation was not adopted, the determination of Au would be interfered by the mass peak of HfOH⁺ and TaO⁺ at the m/z about 196.9, the mass fractions of Hf (0.01%-2.00%) and Ta (0.05%-10.00%) in superalloy were linearly related with the interference amounts of HfOH⁺ and TaO⁺ respectively, and the interference amount was much larger than the Au content in alloy (0.1 μg·g^-1), which cannot be deducted by the linear regression equation of the interference. Linearity relationship between mass fractions of Au and corresponding response values was kept in the range of 0.1-10.0 μg·g^-1, with detection limit (3s) of 0.002 μg·g^-1. The spiked recovery test was made on the actual samples, values of recovery of Au was found in the range of 101%-110%, with RSDs (n=6) of the determined values less than 10%, and the determined values of the prescribed method was in conformity with those of glow discharge mass spectrometry (GD-MS) from ISO/TS 15338:2009(E).