应用多接收器电感耦合等离子体质谱法测定海洋碳酸盐中稳定铅同位素组成

研究了多接收器电感耦合等离子体质谱仪(MC-ICP MS)测定铅同位素比值时,影响测试结果准确度和精密度的主要因素及其优化过程。在优化条件下,10 h内连续30次测定4 ng/mL NIST SRM 981同位素标准溶液铅同位素比值,获得208Pb/206Pb、207Pb/206Pb和206Pb/204Pb相对标准偏差(RSDs)分别为0.005%、0.004%和0.054%。长期监测208Pb/206Pb、207Pb/206Pb和206Pb/204Pb,标准偏差(2SDs)分别为0.000 06、0.000 05和0.006 7。采用NEPTUNE MC-ICP MS法测定了低铅海洋碳酸盐样品中稳定铅的同位素比值,并对南海橙黄滨珊瑚(Porites lutea)和库氏砗磲(Tridacna gigas)进行了分析,得到全流程空白为8～10 pg,重复样误差优于0.1%。经0.50 mol/L HNO3洗脱之后,得到海南珊瑚样品中208Pb/206Pb、207Pb/206Pb的比值分别为2.086 2±0.001 5、0.849 90±0.001 47(n=16);海南砗磲样品中208Pb/206Pb、207Pb/206Pb的比值分别为2.116 9±0.004 2、0.864 81±0.001 62(n=9)。进一步考察了南海海洋碳酸盐中204Pb的同位素比值。分析结果表明,南海海洋碳酸盐中稳定铅同位素比值与中国气溶胶、珠江三角洲大气沉降、黄土及南海海底玄武岩等具有很好的相关性。方法适用于复杂基体高钙低铅的海洋碳酸盐样品中铅同位素比值的分析。

Determination of Lead Isotopic Ratios in Marine Carbonates by Multiple Collectors Inductively Coupled Plasma Mass Spectrometry

The major parameters affecting the accurate and precise determination of lead isotopic ratios by multiple collectors inductively coupled plasma mass spectrometry(MC-ICP MS) were investigated.In the optimized conditions,the relative standard deviations(RSDs) of lead isotopic ratios for NIST SRM 981 standard solution by thirty repeated determinations in 10 h at lead concentration of 4 ng/mL were about 0.005% for 208Pb/206Pb,0.004% for 207Pb/206Pb and 0.054% for 206Pb/204Pb,respectively.Long term stability was tested and the standard deviations(2SD) of 208Pb/206Pb,207Pb/206Pb and 206Pb/204Pb were 0.000 06,0.000 05 and 0.006 7,respectively.A method of NEPTUNE MC-ICP MS for the analysis of stable lead isotopic ratios in trace lead marine carbonates was developed.Hainan corals(Porites lutea) and giant clams(Tridacna gigas) were analysed,the procedural blank of 8-10 pg and the errors of repeated samples better than 0.1% were obtained.After eluted with 0.50 mol/L HNO3,208Pb/206Pb and 207Pb/206Pb in Hainan corals were determined to be 2.086 2 ± 0.001 5 and 0.849 90 ± 0.001 47(n=16),respectively,and 208Pb/206Pb and 207Pb/206Pb in Hainan giant clams were 2.116 9 ± 0.004 2 and 0.864 81 ± 0.001 62(n=9),respectively.The 204Pb ratios of marine carbonates in South China Sea were also reported.The results showed that the lead isotopic ratios of marine carbonates in South China Sea were related to Chinese aerosols,atmospheric deposits of Pearl River Delta,loess,basalts from the South China Sea,etc.The method could be applied in the determination of lead isotopic ratios in marine carbonates that have low lead concentration but complicated matrix with high calcium concentration.