Determination of trace elements in high-purity quartz samples by ICP-OES and ICP-MS: A normal-pressure digestion pretreatment method for eliminating unfavorable substrate Si.

The analysis of siliceous matrix samples may adopt a two-step pretreatment, which includes melting with ammonium hydrogen fluoride and redissolving with nitric acid. However, the residual of substrate silicon unfavorable to the determination of trace elements in the samples due to serious matrix effects. Here, a new digestion method using simultaneously both ammonium bifluoride and nitric acid under normal pressure was developed for high-purity quartz sand sample. The digestion pretreatment is a two step process: melting/dissolving with both ammonium bifluoride and nitric acid at 200 °C for 2 h, and evaporating the solution at 250 °C to dryness. As confirmed by XRD analysis, silicates in the sample were converted to (NH)SiFNO in the melting/dissolving step. TGA analysis shows that the generated (NH)SiFNO could be decomposed and evaporated completely at 250 °C, which ensured a complete removal of silicon by the followed evaporation of the solution at 250 °C. As a result, the followed ICP-OES and ICP-MS analysis needed a solution dilution of only 100 times for the determination of Ca, Mg, Al, Rb, Ba, REE and other trace elements. The new method was applied to the analysis of three certified reference materials, and the results were well consistent with the standard value with RSD% values between 0.62% and 9.73%. Therefore, this method can be applied to the analysis of trace elements in high purity silica-based samples, with the advantages of time-saving, small dilution factor (only 100 times) and low detection limit.