Abstract
The properties of a membrane electrode made of vinyl chloride polymer containing cuprous iodide precipitate were studied in detail. The applications of this membrane electrode as an indicator electrode for potentiometric titration and ion-exchange chromatography were discussed.
The precipitate-impregnated membrane was made for the addition of about 50 weight percent of cuprous iodide precipitate to the vinyl chloride polymer. The membrane was usually ca. 0.30.4 millimeter in thickness and was mounted to the end of a 10 mm diameter polyethylene tube. Untreated membrane electrode was preconditioned by soaking in 0.2M potassium iodide solution for over night.
Cuprous iodide membrane gives a potential correspond to the activities of cupric, cuprous and iodide ions. The potential gradient of cuprous ion was completely contrary to that of cupric or iodide ion.
The value of the slope of potentials vs. logarithmic concentration was approximately 32 mV for cupric ion, 40 mV for iodide ion and -42 mV for cuprous ion in the concentration range between 10-2M and 10-5M of those ions. This fact suggests that the potential of this electrode contains the redox potential of cupric/cuprous couple which can be described as follows and would be electron conductive nature.
Em = Const.+0.0592 log[Cu2+]/[Cu+] at 25°C
At the 0.2M concentration level of Na+, K+, Cl-, SO42-, NO3- and CH3COO- or 0.1M NH4+, Br- and 0.050.1M common cations such as Cd2+, Pb2+, Zn2+ Ca2+, Mg2+ etc. showed no appreciable interference with this membrane potential up to 10-4M cupric ion.
The response time for the cupric ion was fairly short and reaches equilibrium within twenty seconds after the electrode was immersed in the test solution. It should be possible to employ this electrode for the continuous monitoring of chromatography.
The well defined reversed S shape of the titration curve could be obtained in potentiometric titration of copper ion with EDTA in an acetate solution. Similar results were obtained in precipitation titration of copper with sodium tetraphenylborate in an acetic acid medium using ascorbic acid as the reducing agent.
This electrode could be used to obtain elution curves in ion-exchange chromatography, and satisfactory results were obtained for the analysis of copper ion using 0.1M calcium chloride as effluent.
