以铅离子选择性电极为指示电极,用 Pb~(2+)为滴定剂对水泥和石膏中 SO_3的测定已引起国内分析工作者的重视。此方法的关键在于如何快速、可靠地分离干扰测定的 C_a~(2+)。采用碳酸钠沉淀除 C_a~(2+),一方面 C_a~(2+)不易完全除尽,另一方面用 HClO_4中和滤液必然引入大量ClO_4~-,使电位突跃变小。采用静态离子交换 Lead ion selective electrode as the indicator electrode, Pb ~ (2+) as a titrant on cement and gypsum in the determination of SO_3 has drawn the attention of domestic analysts. The key of this method lies in how to quickly and reliably separate the C_a ~ (2+) from interference determination. Addition of sodium carbonate precipitation except C_a ~ (2+), on the one hand C_a ~ (2+) is not easy to completely eliminate, on the other hand with HClO_4 and the filtrate will inevitably introduce a large number of ClO_4 ~ - so that potential jumps become smaller. Using static ion exchange