Rapid and accurate determination of gold in geological materials by an improved ICP-MS method

Abstract

Accurate determination of gold (Au) in geological materials by inductively coupled plasma mass spectrometry (ICP-MS) is suffered to significant Ta and Hf oxide interferences. An improved method based on Ar aerosol dilution ICP-MS after aqua regia extraction was developed for the trace Au determination in geological samples. Over 95% of Hf and 99.5% Ta was removed in the extraction procedure, and the residual Ta or Hf oxides were successfully eliminated by adding 0.85Lmin−1 Ar to the sample aerosol prior to ICP plasma. The yields of interfering oxide ions were as low as 0.076% (TaO+/Ta+) and 0.021% (HfOH+/Hf+). In addition, to further improve the signal to background ratio for ultra-trace Au (subngg−1) determination, 3mLmin−1 CH4 was added to ICP plasma for increasing the Au poor sensitivity (3.8-fold) and decreasing the background signal (2.7-fold). The limit of quantification (LOQ, 10σ) for the developed method was 0.014ngg−1. This method was evaluated by 39 soils, sediments, and rock standard reference materials (SRMs) and the results of all SRMs were found to agree well with the certified values. It has potential as a routine method for the determination of trace levels of Au in various geological samples.