Amperometric response of solid-contact ion-selective electrodes utilizing a two-compartment cell and a redox couple in solution

Abstract

• The amperometric response of ion-selective electrodes (ISEs) was characterized utilizing a two-compartment cell. • ISEs served as potentiometric transducer when connected as reference electrode. • The amperometric response was reversible and reproducible. • The amperometric signal was optimized by applying a potential equal to the half-peak potential (E p/2 ) of the redox couple. An alternative transduction method for ion-selective electrodes (ISEs) is studied by utilizing oxidation/reduction of a Fe(CN) 6 3-/4- redox couple dissolved in solution. Two compartments are employed as electrochemical cell, connected by an Ag/AgCl bridge. A K + -selective solid-contact ISE (K + -SCISE) with reduced graphene oxide as solid contact works as reference electrode (RE) and is placed in the sample solution compartment. A gold electrode acting as working electrode (WE) and a platinum as counter electrode (CE) are placed in the detection compartment with a solution containing the Fe(CN) 6 3-/4- redox couple. As the primary ion (K + ) concentration changes, the potential of the K + -SCISE will change accordingly. Since the potential between WE and RE is kept constant by using a potentiostat, any change in the concentration of primary ion K + will result in an oxidation/reduction current from the Fe(CN) 6 3-/4- redox couple at the surface of the Au WE, causing a current flowing between the Au WE and Pt CE. The diffusion-limited current from oxidation/reduction of the Fe(CN) 6 3-/4- redox couple is linearly proportional to the logarithm of the activity of the primary ion within a certain concentration range of the primary ion. The reversibility and reproducibility of the amperometric response from oxidation/reduction of Fe(CN) 6 3-/4- is proven in this work. A unique feature of this method is that current signal can be enlarged by increasing the geometric surface area of the WE. The amperometric response of the Fe(CN) 6 3-/4- redox couple is highly dependent on the applied starting potential. The sensitivity of the amperometric response can be optimized by applying a potential equal to the half-peak potential (E p/2 ). Furthermore, the amperometric response is applied for determination of K + ion concentration in such a demanding matrix as human blood serum.