自动电位滴定法测定海水中的钙

Automatic Potentiometric Titration for the Determination of Calcium in Seawater

在硼砂缓冲液调节pH条件下,以EGTA(乙二醇二乙醚二胺四乙酸,C14H24N2O10)为滴定剂,用钙离子选择性电极指示终点的自动电位滴定法测定海水中的钙。与用指示剂判断终点的方法相比,可减少目测终点的人为误差。为了提高分析的准确度和精密度,本文对电位滴定仪的工作条件进行实验优化。结果表明最优条件为采用动态等当点滴定(DET)模式,起始滴定剂加入所需体积的85%~90%,最大加液量0.5mL、最小加液量0.1mL,等待时间和暂停时间均为30s,测量点密度1。此条件下信号漂移情况小于0.5mV/min,结果精确可靠,适用于海水中钙的测定。

An automatic potentiometric titration method was applied to determine the concentration of calcium in seawater using EGTA （glycol-bis-（2-aminoethylether） N, N, N＇, N＇-tetraacetic acid,C14 H24N2O10） as titrant solution and the end point was indicated with a calcium ion selective electrode. Compared with the judgment of the titration end point with an indicator reagent, the automatic potentiometric titration shows convenience to reduce the artificial error. In order to improve the analytical accuracy and precision, the working conditions were tested and the optimization was carried out. The response of the calcium ion selective electrode was rapid to calcium in seawater but extended with the addition of EGTA titrant. Thus, the dynamic equivalent point titration （DET） was chosen as the titration mode. 85%-90% of the required volume of EGTA was added before titration with pause time of 30 s. The minimum and maximum volumes of increment during titration should be 0.1 and 0.5 mL with the density of 1 and the waiting time of 30 s for potential response of the electrode. This method is sat- isfied for the determination of calcium in seawater.