镓(Ⅲ)-铬黑T络合吸附波的研究和分析应用——Ⅱ.镓(Ⅲ)-铬黑T的电化学行为及其反应机理

Adsorption Wave of Gallium(Ⅲ)-Eriochrome Black T and Its Analytical Application——Ⅱ. The Electrochemical Behaviour and the Reaction Mechanism of Gallium(Ⅲ)-Eriochrome Black T Complex

在NaAc-HAc介质(pH5.3)中,铬黑T(EBT)和Ga(Ⅲ)-EBT分别于-0.40V和-0.63V产生的峰电流具有吸附特性,均为不可逆电极反应过程。测得EBT和Ga(Ⅲ)-EBT的电子传递系数(α)分别为0.38和0.58,电子转移数(n)和质子数(m)均为2°EBT在电极表面的饱和吸附量(Г_0~S)为5.6×10^(-10)mol/cm^2。在pH4.8～5.6间,EBT(H_3L)主要以H_2L^-形式存在;Ga(Ⅲ)与不同浓度的EBT形成组分比分别为1:1和1:2:两种络合物,相应累积稳定常数K_1=7.2×10^(12),K_2=5.3×10^(25)。提出了它们的电极反应机理,并对温度试验过程中产生的“热色(电)效应”进行了探讨。

The peak currents (P_1,P_2) of eriochrome black T (EBT) and Ga(Ⅲ)-EBT at-0.40 and -0.63 V (vs. SCE) in the NaAc-HAc buffer solution (pH 5.3) have an adsorptive character,and the electrode reaction process was irreversible.The electronic transfer coefficient (a), the number of electrons (n) and protons (m) involved in the electrode reaction of EBT and Ga(Ⅲ)-EBT were estimated to be 0.38 and 0.58 for a, 2 for n and m,resp ctively. The amounts of saturated adsorption of EBT on the electrode surface (Г) were calculated to be about 5.6×10^(-10)mol/cm^2. H_2L^- as the main form of EBT(H_3L) existed in the buffer solution at pH 4.8～5.6; meanwhile the corresponding ratio of Ga(Ⅲ) to EBT under different concentration of EBT was 1:1 (C_(EBT)<1×10^(-6)mol/L) and 1:2 (C_(BT)>1×10^(-6)mol/L); the corresponding consecutive stability constants K_1 and K_2 were calculated to be about 7.2×10^(12) and 5.3×10^(25), respectively. The mechanism of their electrode reaction was presented, and a strong but reversible effect of the temperature on the peak current and the colour change of the solution was discussed.