The influence of spontaneous charging/discharging of conducting polymer ion-to-electron transducer on potentiometric responses of all-solid-state calcium-selective electrodes

Abstract

The effects of spontaneous charging/discharging of a conducting polymer used as an ion-to-electron transducer on the linear responses range and selectivities of cation-selective all-solid-state electrodes are discussed. It was shown that the above processes occurring in electrolytes of relatively high activity (as traditionally used for conditioning) affect the transducer ion content. Hence, the recorded responses, especially in diluted electrolytes are influenced. Careful consideration of the above processes offers the possibility of tailoring the all-solid-state sensor detection limit and selectivity. As a model system, Ca-selective all-solid-state electrodes with a plastic, solvent polymeric membrane and anion exchanging conducting poly(pyrrole) film doped with chlorides used as the contact phase was studied; it should be stressed that the transducer layer applied herein was not tailored to bind calcium ions. It was shown that the choice of composition and pH of conditioning solution results in substantially different detection limits of the sensor. In contrast to internal solution ion selective electrodes, pretreatment procedures can be applied to switch between the different response patterns of the same sensor. On the other hand, the induced responses are stable enough to enable the analytical application of the electrode. The sensor can be optimized to obtain linear responses within an activity range from 0.1 to 10 −9 M CaCl 2 or to achieve unbiased selectivity coefficients. On the other hand, the log K Ca , J pot values obtained were equal to −9.3 for K +, −7.6 for Li + and −9.6 for Mg 2+, respectively, more favorable values than those reported for tailored internal solution electrodes.