铅试金富集-高分辨率连续光源石墨炉原子吸收光谱法测定地球化学样品中痕量金铂钯

Au、Pt和Pd在自然界矿石中丰度很低且分布不均匀,具有块金效应,准确测定其含量一直是地球化学样品分析中的难题。采用铅试金法对样品中的Au、Pt和Pd进行分离并富集于合粒中,合粒经王水处理溶解,用高分辨率连续光源石墨炉原子吸收光谱法(HRCS-GFAAS)进行测定,建立了地球化学样品中痕量Au、Pt和Pd的测定方法。实验表明:采用实验制备提纯的碱式碳酸铅替代商品试剂氧化铅作为捕集剂,可大幅度降低铅试金流程中待测元素Au、Pt和Pd的空白值,且空白值非常稳定;处理合粒时,先用硝酸溶解合粒中银,再加入盐酸形成王水将Au、Pt和Pd完全溶解,滴加NaCl溶液,使Au、Pt和Pd以稳定的卤络酸钠盐形式存在于溶液中;采用连续光源原子吸收光谱仪的高分辨率分光系统,待测元素的连续光源原子吸收光谱分辨率均不大于0.001 49 nm/pixel,可将Au、Pt和Pd的原子吸收谱线与干扰谱线完全分开,故样品中共存元素对Au、Pt和Pd所测谱线的干扰可忽略。在选定的实验条件下,Au、Pt和Pd的吸光度与其对应的质量浓度运用二次方程最小二乘法拟合校准曲线,各元素校准曲线的决定系数(R²)分别为0.999 6、0.999 9和0.999 9;特征浓度分别为0.341、2.964和0.630 (ng/mL)/1%A。将实验方法应用于地球化学样品(土壤基质)中Au、Pt和Pd的测定,结果的相对标准偏差(RSD,n=5)介于6.2%～9.6%之间。将实验方法应用于土壤和岩石(橄榄岩、辉石)等标准物质中Au、Pt和Pd的分析,测定值与标准值吻合良好。

Determination of trace gold,platinum and palladium in geological samples by lead fire assay pre-concentration high resolution continuum source graphite furnace atomic absorption spectrometry

The abundance of gold (Au), platinum (Pt) and palladium (Pd) in natural ores is very low and the distribution is nonuniform. Due to the nugget effect, the accurate determination of their contents is always a challenge in analysis of geochemical samples. Au, Pt and Pd in samples were separated and enriched in alloy granule by lead fire assay method.The alloy granule was dissolved with aqua regia and then determined by high resolution continuum source graphite furnace atomic absorption spectrometry (HRCS-GFAAS). The determination method of trace Au, Pt and Pd in geochemical sample was established. The experiments indicated that: when the purified basic lead carbonate prepared in experiment was used to replace the commercial lead oxide agent as the trapping agent, the blank values of Au, Pt and Pd in lead fire assay could be greatly reduced and very stable. During the treatment of alloy granule, nitric acid was firstly used to dissolve the silver in alloy granule, then hydrochloric acid was added to form aqua regia to fully dissolve Au, Pt and Pd. NaCl solution was dropwise added to make Au, Pt and Pd exist in solution in the form of stable sodium halogenate. The high resolution beam splitting system of continuum source atomic absorption spectrometer was used. The resolutions of testing elements in spectra were all not more than 0.0014 9 nm/pixel, which guaranteed the complete separation of atomic absorption lines and interference lines of Au, Pt and Pd. The interference with lines of Au, Pt and Pd caused by coexisting elements in sample could be ignored. Under the selected experimental conditions,the calibration curves of Au,Pt and Pd were fitted by the least square method using the absorbances and the corresponding mass concentrations. The determination coefficient (R²) of calibration curve of Au,Pt and Pd was 0.999 6,0.999 9 and 0.999 9, respectively. The characteristic concentration was 0.341, 2.964 and 0.630 (ng/mL)/1%A. The proposed method was applied for the determination of Au, Pt and Pd in geochemical samples (soil matrix). The relative standard deviations (RSD,n=5) of determination results were between 6.2% and 9.6%. The experimental method was used to analyze Au, Pt and Pd in certified reference materials of soil and rock (olivinite and pyroxene), and the found results were in good agreement with the certified values.