大量锆存在下铪镧钼杂多酸-耐尔蓝体系测定铪

Spectrophotometric Determination of Hafnium in the Presence of Large Amount of Zirconium in the Nile Blue-Molybdolanthanohafnic Acid System

本文研究了耐尔蓝(NB)-铪镧钼杂多酸(HfLaMo-聚乙烯醇(PVA)体系测定铪的超高灵敏光度法。在PVA存在下,铪、镧和钼酸铵形成杂多酸,继而与耐尔蓝形成离子缔合物。其适宜条件为[HClO_4]=1.2mol/L,[La^(3+)]=2.9×10^(-7)mol/L,[MoO_4^(2-)]=1.1×10^(-3)mol/L,[NB]=2.7×10^(-6)mol/L,PVA0.08％。离子缔合物的最大吸收波长在590nm,表观摩尔吸光系数ε值为1.5×10~7L·mol^(-1)·cm^(-1),至少稳定96h,服从比耳定律范围为0～250ng/25ml。考察了35种共存离子的影响,容许200倍量Zr(Ⅳ)、As(Ⅲ),300倍量TiO_2、Sb^(3+)、SiO_3~2,100倍量Ge(Ⅳ)及10倍量P(Ⅴ),大多数元素不干扰,几种干扰可用溶剂萃取分离。本法已用于岩矿中铪的测定,结果满意。用摩尔比法和平衡移动法测定缔合物的摩尔比为Hf:La=1:3,探讨了反应机理。

A highly sensitive spectrophotometric determination of hafnium has been studied. Hafnium (Ⅳ) and lanthanum (Ⅱ) react with ammonium molybdate to form the ion associated complex of heteropoly molyb-dolanthanohafnic acid (HfLaMo)and nile blue (NB) in the presence of polyvinyl alcohol (PVA). The optimum condition for the determination of hafnium is CHClO4]= 1.2mol/L, [La3+] = 2. 9×10-7mol/L, [MoO42-]=1.1×10-3mol/L,[NB] = 2. 7×10-6mol/Land 0. 08%PVA. The apparent molar absorptivity of the ion associate complex was found to be 1. 5 × 107L. mol-1. cm-1at 590nm,and it was stable for more than 96h. Beer's law is obeyed in the range of 0 to 250ng/25ml for hafnium (Ⅳ). Tolerable amounts have been shown for 35 foreign ions. The method is proved to be satisfactory for the determination of hafnium (Ⅳ)in minerals. The molar ratio of Hf(Ⅳ)to La( Ⅱ)in ion associate complex was established to be 1 : 3 by molar ratio method and equilibrium movement method. The reaction mechanism has been discussed.