离子选择性电极法测定氟石膏中氟

Determination of fluorine in fluorgypsum by ion selective electrode

建立离子选择电极法测定氟石膏中氟含量的分析方法。样品以氢氧化钠为熔剂在400℃熔融分解,冷却后用40~50℃热水浸取熔融物,氟石膏中钙、铝、铁、镁等金属离子以氢氧化物沉淀的形式被除去,然后以溴甲酚绿为指示剂,用硝酸和氢氧化钠调节溶液pH值为5.5~6.5,以饱和甘汞电极为参比电极,氟离子选择电极为指示电极,采用离子计进行测定。结果表明,氟的质量浓度在0.00~6.00 mg/L范围内其对数与电位值呈良好的线性关系,线性方程为E=–55.721lgc+175.50,线性相关系数为0.9996,检出限为0.0019 mg/L,测定结果的相对标准偏差为1.63~2.87%(n=11),样品加标回收率为96.33%~103.18%。该方法精密度及准确度好,灵敏度高,适用于氟石膏中氟的测定。

A method for the determination of fluorine in fluorogypsum by ion selective electrode was established.The sample was melted and decomposed at 400℃with sodium hydroxide as flux.After cooling,the molten product was leached with hot water of 40–50℃.The calcium,aluminum,iron,magnesium and other metal ions in fluorogypsum were removed in the form of hydroxide precipitation.Then,bromocresol green was used as indicator,nitric acid and sodium hydroxide were used to adjust the pH value of the solution to 5.5–6.5.The determination was carried out with an ion meter using saturated calomel electrode as reference electrode and fluoride ion selective electrode as indicator electrode.The results showed that the logarithm of mass concentration of fluoride had a good linear relationship with the potential value in the range of 0.00–6.00 mg/L.The linear equation was E=–55.721lgc+175.50,the linear correlation coefficient was 0.9996,and the detection limit was 0.0019 mg/L.The relative standard deviation of the determination results was 1.63%–2.87%(n=11),and the recoveries were 96.33%–103.18%.The method is suitable for the determination of fluorine in fluorogypsum with good precision,accuracy and sensitivity.