ICP-MS分析用地质样品制备过程中Nb、Ta等元素的特殊化学行为

Hydrofluoric acid is difficult to be effectively purified with sub-boiling distillation in terms of Ta, Nb and some other high field strength elements (HFSE), which potentially suggests that Nb and Ta could be ” evaporated” accompanying HF. On the other hand, Nb and Ta could be ”lost” in diluted nitric acid solution due to hydrolysis. Our routine analyses of geological samples digested with PTFE Bomb (HF+ HNO3) indicate that these elements were not always lost during sample preparation, which implies that stabilities of Nb and Ta were controlled by some components in addition to HF. In this work, several experiments were conducted to investigate the specific behavior of Nb and Ta during sample digestion with PTFE Bomb for ICP-MS analysis. The results indicate that major metal components (e.g., Al, Fe, Mg, and Ca) in rocks could play a comparable role in stabilizing Nb and Ta species. Ta in diluted nitric acid solution (i.e.2% HNO3) could be stabilized by concentrated metal cation (e.g., Al/Ta ＞ 104), which are consistent with the generally good results of routine analyses of geological samples. Alternatively, enough amounts of HF could prevent hydrolysis of Ta in diluted nitric acid solution as well to obtain satisfactory recovery. Nb shows different chemical behavior from Ta during the chemical preparation for ICP-MS analysis. Ta is more easily hydrolyzed/polymerized than Nb in diluted nitric acid solution. On the other hand, our work suggests that hydrofluoric acid could be effectively purified in terms of Nb and Ta with sub-boiling distillation by mixing with additional concentrated metal matrix (e.g., Fe, Al).