Selectivity coefficients for amperometric sensors

Selectivity coefficients (k(amp)(ij)) are introduced as well-defined measures of the selectivity of amperometric sensors. For any amperometric device the total current response in the presence of interfering species (j) can be described by the general equation; i(t) = K(C(i) + Sigmak(amp)(ij)C(j)), where i is the target analyte. Equations are derived for k(amp)(ij) under different conditions common in amperometric sensing. Factors influencing the selectivity coefficients of amperometric probes, including the recognition and transduction mechanisms, the controlled-potential operating technique, and the transducer geometry are discussed. The selectivity coefficient strategy is illustrated experimentally with two widely used applications of amperometric devices, the anodic monitoring of dopamine at Nafion-coated electrodes and the biosensing of glucose at glucose-oxidase enzyme probes. It is anticipated that the selectivity coefficient strategy will become widespread in amperometric devices, and for chemical sensors in general, and will not be limited only to potentiometric probes.