镍锍试金富集-电感耦合等离子体质谱法测定地质样品中超痕量铂族元素

Ultratrace Platinum Group Elements in Geological Samples by Inductively Coupled Plasma-Mass Spectrometry with Nickel Sulfide Fire Assay

铂族元素(PGEs)六项元素钌、铑、钯、锇、铱和铂的物理化学性质相近,在地壳中丰度极低且分布不均匀,且具有明显的粒金效应,长期以来准确测定其含量始终是岩矿测试的难题。镍锍试金取样量大,可定量分离富集铂族元素,通常被应用于PGEs分析,但将其应用于超痕量PGEs分析的关键问题是流程空白高,质谱干扰严重。本文报道了一种同时测定样品中超痕量铂钯铑铱锇和钌的方法。检查全流程试剂空白后,使用镍锍试金富集样品中的PGEs,经杂质分离,利用电感耦合等离子体质谱(ICP-MS)动能歧视模式测定六项元素,有效地降低了质谱干扰。结果表明,方法的空白主要来自盐酸和捕集剂镍粉,选择合适厂家的试剂或对试金配料进行提纯,可降低全流程空白。同时,使用ICP-MS法测定六项元素时,在标准模式下,铂和钯的检出限小于0.2ng/g,铑、铱和锇的检出限小于0.02ng/g,钌的检出限大于0.1ng/g,钌的检出限无法满足超痕量PGEs的测定要求。使用动能歧视模式后,钌的背景等效浓度比标准模式降低近两个数量级,从而消除了镍对钌的质谱干扰,钌的检出限降低至0.005ng/g,使六项元素检出限同时满足超痕量PGEs测定要求。该方法用于分析土壤(GBW07288、GBW07294)、水系沉积物标准物质(GBW07289),六项元素的结果与标准值符合,相对误差为−10.9%~11.8%,相对标准偏差为3.85%~9.37%,加标回收率为92%~110%。该方法流程较短、操作简便,满足大批量地质样品中超痕量PGEs的检测要求。

Pt,Pd,Rh,Ir,Os and Ru are platinum group elements(PGEs)with similar properties.Due to the low abundance as well as the nugget effect,the accurate determination of PGEs has been a challenge for rock and mineral analysis.Fire assay methods with large sample weights were developed to separate and preconcentrate PGEs,however,there are still difficulties to accurately determine ultratrace PGEs because of the high reagent blanks and the matrix effect.A method of nickel sulfide fire assay combined with ICP-MS simultaneous determination of ultratrace PGEs in samples was established.The results showed that the blank mainly comes from hydrochloric acid and nickel collector when using nickel sulfide fire assay to capture PGEs.The intensities of PGEs were detected by ICP-MS in standard mode and kinetic energy discrimination.In standard mode,the detection limits were 0.2ng/g for Pt and Pd,and 0.02ng/g for Rh,Ir and Os,but it couldn’t reach 0.1ng/g for Ru.In kinetic energy discrimination,the background equivalent concentration of Ru was two orders of magnitude lower than that in the standard mode.With the matrix effect of Ni effectively eliminated,the detection limits reached 0.005ng/g for Ru.The detection limits for PGEs required by geochemical exploration were achieved.The certified reference materials of soil(GBW07288,GBW07294)and stream sediment(GBW07289)were analyzed to test the method.The determined values were in good agreement with the certified values.The relative errors were between−10.9%and 11.8%,the relative standard deviations(RSD,n=12)were 3.88%−9.37%,and the spiked recoveries were 92%−110%.This method is simple,rapid and meets the requirements of ultratrace PGEs determination in large quantities of geological samples.