DETERMINATION OF POTASSIUM IN SILICATE ROCKS BY FLAME ATOMIC EMISSION SPECTROMETRY AFTER ULTRASOUND DISSOLUTION

This work presents the development of an analytical method for sample preparation aiming at the K determination in silicate rocks (basalt, monzogranite and shale fines) following ultrasound dissolution and analysis by F AES. Sample preparation method was optimized by using fractional factorial designs. The following optimal conditions were obtained for each silicate rock: 0.1 g of sample mass for any of the three samples, and volumes of HNO3, HCl and HF, respectively, of 2.5, 0.8 and 2.5 mL for basalt; 3.5, 0.8 and 2.5 mL for monzogranite, and 2.5, 1.0 and 2.0 mL for shale fines. Sample dissolution was achieved by using the ultrasound bath at room temperature (25 °C) for 1 hour. The accuracy was evaluated through the analysis of two certified reference materials, for which there was no statistical difference between the certified and the found K concentration values (95% confidence level). The K concentrations determined were: 1.45 ± 0.01 for basalt; 4.19 ± 0.03 for monzogranite and 1.60 ± 0.02 for shale fines. The developed method presented accurate and reliable results for K amounts in silicate rocks and is simple and safe, which are important features for the implementation of a methodology as a routine analysis.

本研究开发了一种针对硅酸盐岩石（玄武岩、二长花岗岩及页岩粉）中钾（K）元素测定的样品前处理分析方法，该方法采用超声消解结合火焰原子发射光谱（Flame Atomic Emission Spectroscopy, FAES）完成检测。本研究通过部分因子设计对样品前处理流程进行了优化，针对三种硅酸盐岩石分别得到如下最优实验条件：三种样品的称样量均为0.1 g；玄武岩的硝酸（HNO₃）、盐酸（HCl）、氢氟酸（HF）用量分别为2.5 mL、0.8 mL、2.5 mL；二长花岗岩的三种酸用量分别为3.5 mL、0.8 mL、2.5 mL；页岩粉的三种酸用量分别为2.5 mL、1.0 mL、2.0 mL。样品消解在室温（25 ℃）超声浴中进行，消解时长为1小时。本研究采用两种有证标准物质（Certified Reference Material, CRM）对方法的准确度进行验证，结果显示，在95%置信水平下，实测钾浓度与认定值之间无统计学差异。三种样品的测定钾浓度分别为：玄武岩1.45 ± 0.01，二长花岗岩4.19 ± 0.03，页岩粉1.60 ± 0.02。所开发的方法对硅酸盐岩石中的钾元素定量结果准确可靠，且操作简便安全，这些特性对于该方法作为常规分析手段的落地应用具有重要价值。