锡试金富集-微波消解-石墨炉原子吸收光谱法测定地球化学样品中痕量铑和铱

铑和铱在工业领域具有重要战略地位,但其在自然界含量极低、分布不均,准确测定其含量一直是地球化学样品分析中的难题。采用锡试金富集样品中痕量的铑和铱,用压力机将锡扣压成锡片后,经盐酸溶解并过滤,以王水(1+1)为介质用微波消解法处理沉淀及滤纸,用石墨炉原子吸收光谱法(GF-AAS)对样品溶液中的铑和铱进行测定,建立了地球化学样品中铑和铱的测定方法。实验表明,以锡粉为捕集剂,锡试金流程中铑和铱的空白值远低于锍镍试金和铅试金的空白值。在选定的实验条件下,Rh和Ir的吸光度与其对应的质量浓度在12.5～50 ng/mL范围内运用二次方程最小二乘法拟合校准曲线,校准曲线的决定系数分别为0.999 6和0.999 2。铑和铱的特征浓度分别为0.183和1.367 ng/mL,检出限分别为 0.015和0.018 ng/g。将实验方法应用于铂族元素地球化学标准物质中Rh和Ir的测定,测定值与标准值吻合良好,相对标准偏差(RSD, n=6)为3.6%~12.6%。将实验方法应用于铬铁矿和土壤样品分析,Rh和Ir测得结果的相对标准偏差(n=6)为3.7%～7.3%,加标回收率为85%～108%。

Determination of trace rhodium and iridium in geochemical samples by graphite furnace atomic absorption spectrometry with tin fire assay and microwave digestion

Rhodium and iridium had an important strategic position in the industrial field. However, their contents in nature were extremely low with nonuniform distribution. The accurate determination of rhodium and iridium contents was always a difficulty in the analysis of geochemical samples. Trace rhodium and iridium in sample were enriched by tin fire assay. The tin button was pressed to tin sheet with press machine followed by dissolution with hydrochloric acid. After filtration, the precipitate and filter paper were treated by microwave digestion with aqua regia (1+1) as the medium. The contents of rhodium and iridium in sample solution were determined by graphite furnace atomic absorption spectrometry (GF-AAS). A determination method of rhodium and iridium in geochemical samples was established. The experimental results showed that the blank values of rhodium and iridium in process of tin fire assay were much lower than those in nickel fire assay and lead fire assay when tin powder was used as the collector. Under the selected experimental conditions, the calibration curves were fitted by the least square method of quadratic equation based on the absorbance of rhodium and iridium as well as their corresponding mass concentration in range of 12.5-50 ng/mL. The determination coefficients of the calibration curves were 0.999 6 and 0.999 2, respectively. The characteristic concentrations of rhodium and iridium were 0.183 ng/mL and 1.367 ng/mL, and the limits of detection were 0.015 ng/g and 0.018 ng/g, respectively. The experimental method was applied to the analysis of rhodium and iridium in certified reference materials of geochemical sample of platinum family elements. The results were in good agreement with the certified values. The relative standard deviations (RSDs, n=6) were between 3.6% and 12.6%. The proposed method was applied to the analysis of chromite and soil samples. The RSDs (n=6) of determination results were between 3.7% and 7.3%. The recoveries were between 85% and 108%.