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本文研究以硫脲和抗坏血酸-邻菲罗啉-硫脲体系作释放剂,在室温下从 Pd-EDTA 和 Cu-EDTA 络合物中分别将 EDTA 定量释放,探讨了最佳反应条件。利用掩蔽效应,高选择性地释放析出法,络合滴定钯和铜。加入过量的 EDTA 使之与 Pd~(2+)和 Cu~(2+)完全络合后,过剩的 EDTA 在pH4.5～5.5时,以二甲酚橙(X·O)为指示剂用 Pb(NO_3)_2进行回滴;再加硫脲(TU)使 Pd-EDTA 络合物,转化为〔Pd(TU)_2)〕~(2+)络合物,并且释放析出与钯等当量的 EDTA,再以 Pb(NO_3)_2进行回滴定(测定出钯量)。然后加入抗坏血酸(VC)-Phen 催化释放体系,使 Cu-EDTA 络合物转化为〔Cu(TU)_4〕~+,并且释放出与铜等当量的 EDTA 再用 Pb(NO_3)_2进行回滴定(测出铜量)。对各种阳离子的干扰做了实验,证明没有什么影响。实现了在同一试液,同一pH 值、同一指示剂,同一标液、选择性的连续络合滴定钯、铜。操作简便、快速、准确可靠。
In this paper, the thiourea and ascorbic acid-o-phenanthroline-thiourea system as a release agent, EDTA at room temperature from the EDTA-EDTA and EDTA were released quantitatively to explore the optimal reaction conditions. With the masking effect, the precipitation method is released with high selectivity and the palladium and copper complexes are complexed. Excess EDTA was completely complexed with Pd 2+ and Cu 2+, and the excess EDTA was eluted with xylenol orange (X · O) as an indicator at pH 4.5-5.5 Pb (NO_3) _2, followed by thiourea (TU) to convert the Pd-EDTA complex to [Pd (TU) _2)] 2+ complex and release equivalent amount of palladium EDTA, followed by Pb (NO_3) _2 back titration (measured palladium). Then the ascorbic acid (VC) -Phen system was added to convert the Cu-EDTA complex to [Cu (TU) 4] ~ +, and an equivalent EDTA with copper was released and titrated with Pb (NO_3) _2 (Measure the amount of copper). Experiments on the interference of various cations proved to have no effect. Realization of the same test solution, the same pH, the same indicator, the same standard solution, selective continuous complexation titration of palladium, copper. Easy to operate, fast, accurate and reliable.