电位滴定法连续测定双氰胺钠及杂质氯化钠含量

Continuous Determination of Sodium Dicyanamide and Its Impurities Sodium Chloride by Potentiometric Titration

采用电位滴定法,以Ag NO3为滴定剂,银电极为指示电极,双盐桥饱和甘汞电极为参比电极,在低温酸性甲醛/异丙醇溶液中,连续滴定氯化钠和双氰胺钠溶液,以二阶微商法确定滴定终点,测定了双氰胺钠及其杂质氯化钠的含量。其原理是利用双氰胺银和氯化银溶度积的差异,在连续滴定过程中会出现两个电位突跃,从而实现分别滴定。实验优化了溶剂的配比及用量,在10 m L甲醛(Na OH中和)+80 m L异丙醇+1 m L硝酸介质中,冰浴条件下测定时,分析结果误差最小。用企业提供的标样验证了方法的准确性,对未知样中双氰胺钠及杂质氯化钠含量的测定结果满意。

By continuous potentiometric titration with an Ag NO3 solution as the titrant,silver electrode as the indicator electrode,double salt bridge saturated calomel electrode as the reference electrode,in the acid formaldehyde/isopropanol solution at low temperature,the levels of sodium dicyandiamide and its impurities of sodium chloride are measured. The titration endpoint is determined by the second order derivative method. The principle of the proposed procedure is that using the solubility product of silver dicyandiamide and silver chloride is quite different in nature. In the continuous titration process,it will be two potential jump,respectively,in order to achieve titration. The ratio and amount of solvents is optimized. In a 10 m L formaldehyde（ neutralised by Na OH） ＋ 80 m L isopropanol ＋ 1 m L nitric acid medium,the measured error is minimized under the ice condition. The procedure is validated by analyzing a standard sample provided by a company,and is further applied for the determination of sodium dicyandiamide and sodium chloride of the unknown samples with satisfactory results.