• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.870-877
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• 1998

With impedance spectrum measurements, impedance was studied in the interface between sample solutions for $K^+-ion$ selective PVC membrane electrode containing neutral carriers [dibenzo-18-crown-6 (D18Cr6) and valinomycine (Val)]. Response characteristics of electrode were examined by measuring AC impedance spectra that were resulted from the chemical structure and the content of carrier, variation of plasticizer, membrane thickness, doping of base electrolytes, and concentration variation of sample solution. Transport characteristics of PVC membrane electrode were also studied. It was found that the equivalent circuit for the membrane in $K^+$ solution could be expressed by a series combination of solution resistance and a parallel circuit consisting of the bulk resistance and geometric capacitance of the membrane system. But the charge transfer resistance and Warburg resistance were overlapped a little in the low concentration and low frequency ranges. The carrier, D18Cr6 was best for electrode and impedance characteristics, and ideal electrode characteristics were appeared especially in case of doping of the base electrolyte[potassium tetraphenylborate(TPB)]. The optimum carrier content was about 3.23 wt% in case of D18Cr6 and Val. DBP was best as a plasticizer. As membrane thickness decreased the impedance characteristics was improved, but electrode characteristics were lowered for membrane thickness below the optimum. In the case of D18Cr6, the selectivity coefficients by the mixed solution method for the $K^+$ ion were the order of $NH_4{^+}>Ca^{2+}>Mg^{2+}>Na^+$.