基于蒸气发生进样技术的高精度镉同位素分析方法及其在古环境研究中的应用

Cadmium isotope analysis has received increasing attention due to its unique characteristics and is being widely used in the study of space, environmental, marine sciences, also in mineralogy etc. However, cadmium isotope application is hindered by the analysis method due to the requirement of high concentration and severe residue Sn interference. In the present project, a novel method for cadmium isotope analysis is proposed based on chemical vapor generation(CVG) sample introduction. The high sample introduction efficiency and capability to separate the analytes from matrix of CVG will be thoroughly investigated to improve the sensitivity and precision of Cd isotope analysis. Specially, our recently developed plasma induced vapor generation method will be applied to the Cd isotope measurement. In plasma-CVG, cadmium ions are efficiently converted to volatile species by plasma induced chemical processes without the use of unstable reducing agents, which is preferable for the trace Cd isotope analysis since its operation reduces the background signals. The optimum CVG conditions and CVG reaction cells will be evaluated in detail. The impact of the measurement time and Cd concentration on the precision of Cd isotope will also be investigated. After that, we will develop high sensitive, high precision Cd isotope analysis method by exploring appropriate MC-ICPMS mass bias correction method. Furthermore, the developed method will be applied in determining the composition of Cd isotopes in several reference materials and typical P-T boundary samples with low Cd concentration. In addition, we will try to investigate the fractionation mechanism of Cd isotopes. The present study would permit us to analyze Cd isotope in low concentration samples, to better understand the fractionation behavior of Cd, and provides a robust high precision method for Cd isotope composition determination in both geological and environmental samples.

由于在天体化学、海洋科学、环境科学及矿床学中有着独特的应用优势，镉同位素引起了人们的广泛关注。本项目我们提出了基于蒸气发生进样(VG)的镉同位素分析方法，发挥VG进样效率高、可分离基体的优势，解决现有Cd同位素分析中对镉浓度要求较高以及Sn、残留树脂等引起的干扰问题，实现低含量镉样品的高精度同位素分析。除常规化学蒸气发生以外，项目重点将我们研发的等离子体蒸气发生应用于镉的同位素分析。与传统蒸气发生相比，等离子体蒸气发生既避免了常规化学试剂的使用，显著降低流程空白，又具有更高的引入效率，非常适合镉同位素分析。通过优化蒸气发生条件与接口技术、确定最佳测量时间和样品浓度、选择合适的校正技术，建立高灵敏、高精度的Cd同位素分析技术。利用建立的方法获取各种标准参考物质和二叠-三叠系(P-T)典型地质剖面低含量样品中镉的同位素组成，进一步研究镉同位素分馏行为和机理，拓宽Cd同位素在古环境研究中的应用。

由于镉独特的地球化学性质，近年来镉同位素在天体化学、海洋科学、环境科学及矿床学研究取得了广泛应用，然而地质样品中镉的浓度一般较低，因此迫切需要解决低浓度镉样品的高精度镉同位素分析难题。本项目围绕痕量镉浓度分析、等离子体蒸气发生、双稀释剂Cd同位素分析方法以及关键过程中镉同位素分馏开展了系列研究，具体主要包括以下几个方面：1）针对地质/环境样品中痕量Cd分析存在干扰、难以准确测定的问题，发展了基于膜去溶进样、等离子体蒸气发生以及微等离子体激发源的Cd浓度准确分析的新方法，实现了不同样品中Cd浓度的灵敏、准确分析；2）开发了喷雾介质阻挡放电等离子体化学蒸气发生、液体阳极等离子体电化学蒸气发生方法与装置，可以实现Pb、Cd、Zn、Sb等多种元素的绿色、高效蒸气发生；3）建立了膜去溶进样-双稀释剂镉同位素高精度分析方法，提出了校正DS和样品比值p影响的策略，解释了常规DS镉同位素分析中基准比值偏移的问题；在此基础上，开发了基于等离子体蒸气发生进样的Pb、Cd同位素灵敏分析方法，通过分析地质标样及样品证实了方法的可靠性；4）探究了光化学溶解与方解石吸附过程中镉同位素分馏行为及影响因素，获得了镉同位素分馏的分馏系数，探讨了分馏机理，有助于拓宽镉同位素在表生环境过程中的应用。项目执行期间共以第一作者或通讯作者发表基金标注的SCI期刊论文18篇，其中Analytical Chemistry 5篇，Journal of Analytical Atomic Spectrometry封面论文1篇；获得授权发明专利3项。