稀土-硅、钙、镁合金中稀土总量的测定历来采用草酸盐重量法,手续繁杂,周期颇长。以后采用了络合滴定法,方法虽然简便,但由于与稀土共存的钍的干扰,使滴定终点不易判断而影响准确度。关于消除稀土络合滴定时钍的干扰,国内已有不少报导。例如首先将稀土和钍以氟化物或草酸盐形式沉淀分离,继则在一定的pH介质中以磷酸三丁酯-二甲苯,乙酰丙酮或铜试剂萃取分离钍。文献对含钍2％以上的样品采用六次甲 Rare earth - silicon, calcium, magnesium alloy has always been the determination of the total amount of rare earth oxalate gravimetric procedures complicated, long cycle. After using the complexation titration method, although the method is simple, but due to the coexistence of rare earth thorium interference, titration end point is not easy to judge and affect the accuracy. On the elimination of rare earth complexation titration thorium interference, there have been many reports. For example, rare earth and thorium are first precipitated as fluoride or oxalate, and thorium is extracted and extracted with tributyl phosphate-xylene, acetylacetone or copper reagent in a certain pH medium. Literature on the thorium 2% or more of the sample using six times a