Short-term influence of interfering ion activity change on ion-selective micropipette electrode potential; another factor that can affect the time needed for imaging in potentiometric SECM

The applicability of ion-selective microelectrodes (ISME) in scanning electrochemical microscopy (SECM) in the presence of potentially interfering ions is investigated. Decreasing the time needed for potentiometric SECM imaging is a key aim. It is generally accepted that the long response time of potentiometric cells with high impedance microelectrodes limits the imaging speed that can be obtained without distortion. In this study we show that a change in the activity of interfering ions can result in a short-term electrode potential transient that should be taken into consideration in parameter setting for SECM measurements. The activity step method was employed, using NH₄⁺-ion-measuring micropipettes. Solutions containing equal concentrations of NH₄⁺ ions with or without K⁺ ions were rapidly introduced and the short-term change in electrode potential was recorded. Rapid transient potential signals appeared following the K⁺ activity step in the range where the interfering K⁺ did not affect the long-term electrode potential. The possible influence of this on SECM applications is discussed.