电感耦合等离子体质谱法测定地球化学样品中痕量铑的干扰消除方法探讨

采用电感耦合等离子体质谱法(ICP-MS)测定地球化学样品中痕量Rh时,待测溶液的基体及分子离子干扰严重影响ICP-MS测定¹⁰³Rh的准确性。实验以10 ng/mL 的¹⁷⁵Lu消除基体干扰,以数学校正方程消除多原子离子⁸⁷Sr¹⁶O⁺、⁶³Cu⁴⁰Ar⁺、⁸⁶SrOH、²⁰⁶Pb²⁺对¹⁰³Rh的干扰,最终实现了电感耦合等离子体质谱法测定地球化学样品中痕量Rh。分别详细考察了Cu、Sr、Pb对Rh测定的干扰情况,不仅有效消除了⁸⁷Sr¹⁶O⁺、⁶³Cu⁴⁰Ar⁺、⁸⁶SrOH多原子离子对¹⁰³Rh的测定干扰,而且发现了双电荷离子²⁰⁶Pb²⁺对¹⁰³Rh的测定存在严重的质谱干扰。同时通过向不同浓度Rh的标准溶液中分别加入不同量的干扰元素Cu、Sr及Pb进行试验,得到了对¹⁰³Rh元素进行校正的数学校正方程。实验表明,Rh在0.050～100.0 ng/mL范围内与其对应的信号强度呈良好的线性关系,线性相关系数为0.999 9,方法检出限(3σ)为0.014 ng/g。采用实验方法对铂族元素地球化学一级标准物质中Rh进行分析,结果与认定值的相对误差(RE)为-7.27%～6.15%,相对标准偏差(RSD,n=12)均不大于8.6%。将实验方法应用于云南、四川、新疆等地区不同含量贵金属地球化学样品中Rh的测定,所得结果与锡试金方法符合性较好。

Discussion on elimination of interference in determination of trace rhodium in geochemical sample by inductively coupled plasma mass spectrometry

During the determination of trace rhodium in geochemical samples by inductively coupled plasma mass spectrometry (ICP-MS), the determination accuracy of ¹⁰³Rh was severely affected by the interference of matrix and molecule ions in testing solution. The matrix interference was eliminated with 10 ng/mL ¹⁷⁵Lu as internal standard. The interference of multi-atomic ions such as ⁸⁷Sr¹⁶O⁺, ⁶³Cu⁴⁰Ar⁺, ⁸⁶SrOH and ²⁰⁶Pb²⁺ with the determination of ¹⁰³Rh was eliminated by mathematical correction equation. Consequently, a determination of trace rhodium in geochemical samples by ICP-MS was realized. The interference of Cu, Sr and Pb with the determination of Rh was investigated in detail. The interference of ⁸⁷Sr¹⁶O⁺, ⁶³Cu⁴⁰Ar⁺ and ⁸⁶SrOH with the determination of ¹⁰³Rh was effectively eliminated. Moreover, it was found that the double-charge ion of ²⁰⁶Pb²⁺ had serious mass spectrometry interference with the determination of Rh. Meanwhile, various amounts of interference elements (Cu, Sr and Pb) were added into the standard solution of Rh with different concentrations for test. The mathematical correction equation for ¹⁰³Rh was obtained. The experimental results indicated that the concentration of Rh in range of 0.050-100.0 ng/mL had good linear relationship to its corresponding signal strength with correlation coefficient of 0.999 9. The detection limit of method (3σ) was 0.014 ng/g. The proposed method was applied to the analysis of Rh in primary reference material of geochemical sample of platinum family element. The relative errors (RE) between the found results and certified values were between －7.27% and 6.15%. The relative standard deviations (RSD, n=12) were all not more than 8.6%. The experimental method was used for the determination of Rh in geochemical samples with various precious metal content from Yunnan, Sichuan and Xinjiang, and the results were consistent with those obtained by tin assaying method.