氯离子选择性电极-标准加入法测定碳酸稀土中氯

采用HNO₃(1+ 2)溶解样品,氯则全部以Cl^—形式溶解于溶液中,通过测定溶液中Cl^—质量浓度,即可计算出碳酸稀土中氯含量。试验探讨了在以硝酸钾和柠檬酸三钠为总离子强度调节缓冲溶液(TISAB)体系中,主要以EDTA溶液络合稀土离子,采用氯离子选择性电极-标准加入法测定碳酸稀土中氯含量的方法。结果表明:溶液中Cl^—质量浓度在2.0～40.0 mg/L范围内,EDTA溶液和TISAB溶液用量均为10 mL,Cl^—质量浓度的负对数与相应电极电位(E)呈良好线性关系,线性相关系数为0.999 9;为保证测试结果的准确性,样品和电极响应斜率S值的测定须在同一恒温体系下进行;方法检出限为0.947 mg/L;对于5 mg/L的Cl^—,大量K⁺、Na⁺、NO₃^— 不干扰Cl^—的测定,RE³⁺、Ca²⁺、Fe²⁺、Na⁺最大允许量分别为10.0、4.0、5.5、23 g/L。按照实验方法测定碳酸镧和混合碳酸稀土中氯,结果的相对标准偏差(RSD,n=5)均小于5%;测定值与氯化银比浊法的测定值基本一致。

Determination of chlorine in rare earth carbonate by chloride ion selective electrode with standard addition method

The sample was dissolved with HNO₃(1+2). The chlorine in sample totally existed in solution in form of Cl^-. The content of chlorine in rare earth carbonate could be calculated by measuring the mass concentration of Cl^- in solution. With potassium nitrate and trisodium citrate as total ionic strength adjustment buffer solution (TISAB), the rare earth ions were mainly complexed by EDTA. The content of chlorine in rare earth carbonate was determined by chloride ion selective electrode with standard addition method. The results showed that the negative logarithm of mass concentration of Cl^- in solution was linear to its corresponding electrode potential (E) under the following conditions: the mass concentration of Cl^- in solution was in range of 2.0-40.0 mg/L; the dosage of EDTA solution and TISAB solution was 10 mL, respectively. The linear correlation coefficient was r=0.999 9. In order to guarantee the accuracy of determination results, the determination of sample and electrode response slope (S value) must be conducted in a same constant temperature system. The detection limit was 0.947 mg/L. The determination of Cl^- (5 mg/L) was not interfered by much K⁺, Na⁺ and NO^-₃. The maximum tolerant amount for RE³⁺, Ca²⁺, Fe²⁺ and Na⁺ was 10.0, 4.0, 5.5 and 23 g/L, respectively. The content of chlorine in lanthanum carbonate and mixed rare earth carbonate samples was determined according to the experimental method. The relative standard deviations (RSD, n=5) were less than 5%. The results were consistent with those obtained by silver chloride turbidimetry.