采用氧化物方式高精度测量微量样品钕同位素比值

Precise Measurement of Nd Isotopic Ratio of Micro-Samples Using NdO^+ Method

微量样品Nd同位素比值的高精度测定在地球科学和环境科学研究中具有重要的意义,同时也是同位素测定的难点.对1ng以下的国际标准样品进行了高精度质谱测试.采用新一代高精度热电离质谱计(IsoProbe-T)分别运用Nd+和NdO+测试方法,多次测量常量(≥200ng)和超微量(0.25ng、0.5ng和1ng)Nd标准物质(Ames、JMC和Jndi-1)和实验室内部标准LRIG-Nd溶液.质谱计同位素比值测量均采用静态多接收模式.143Nd/144Nd比值测量的内部精度均优于0.003%.与传统的Nd+测量方式相比,NdO+测量方式具有显著的优势,即有极高的灵敏度,是Nd+分析灵敏度的100倍左右.

Precise measurement of Nd isotopic ratio of micro-samples, being one of the most difficult tasks in measurements of isotopic ratios, plays an important role in research fields of earth and environmental sciences. This study reports the results of precise measurements of Nd isotopic ratios on the solutions of international standard material using less 1 ng samples. Applying the Nd^＋ and NdO^＋ measurement methods, solutions of the standard material （Ames, JMC, and Jndi-1） and the laboratory-own reference material （LRIG-Nd）, which contain ≥200 ng to 0.25 ng Nd samples, were measured by a new thermal ionization mass spectrometer （IsoProbe-T）. Data acquisition during the isotopic measurement was done by using a static mode with a multiple-receiver configuration. Internal and external precisions obtained for all the measurements of ^143 Nd/^144 Nd ratio were better than 0. 003%. Compared with the Nd^＋ method, Nd isotopic measurement using the NdO^＋ method distinguishably displays an advantage in high sensibility of measurement, being about 100 times higher than that by using the Nd^＋ method.