Characteristic evaluation of pencil-drawn carbon electrode by potassium and sodium ion selectivity measurement and energy-dispersive X-ray spectroscopy

This paper explains the ion-sensing mechanism and selectivity evaluation of the pencil-drawn carbon electrode (PCE) employed as a pH electrode in the authors' previous report. The elemental composition of the PCE was found to be C, O, Si, Al, and Na by energy-dispersive X-ray spectroscopy (EDX). The carbon is regarded as the graphite performing electrical conduction, while the other elements formed clay as an ion exchanger. Furthermore, the potential responses to K+ and Na+ were measured, and the selectivity is discussed quantitatively under the Eisenman equation which describes the ion exchanger potential with cation interference. The selectivity coefficients were estimated to be 10−4.10 to 10−3.87 and 10−5.00 to 10−4.89 for K+ and Na+ with n of 4 to 5, respectively. The EDX analysis and selectivity measurement show that the PCE might have ion exchange properties similar to those of a glass electrode and it sufficiently behaves as a pH electrode in wide targets having only slightly interfering cations.