Abstract
The possibility of analysis using charge curve fitting in constant potential coulometric mode instead of using a calibration plot is explored, for the first time. The results are compared with the analysis based on the use of a calibration plot. A Ca2+ ion-selective electrode, with and without an electronic capacitor in series, is used as a model system in pure solutions of CaCl2. Both techniques delivered good results (error within 2%) when the final and the initial concentration values differed by not more than three times. Larger differences result in 10–25% error. The presence of an electronic capacitor in the measurement circuit and in series with the electrode, allows for significantly faster response.
Highlights
The constant potential coulometry method invented in the Bobacka’s group opened new opportunities for the use of ion-selective electrodes (ISEs) [1–3]
Prior to chronoamperometric/coulometric measurements, the ISE response to Ca2+ in pure CaCl2 and in model solutions was controlled by the electromotive force (EMF) measurements
The standard EMF values vary between the three replicate electrodes, which is typical for solid-contact ISEs [16]
Summary
The constant potential coulometry method invented in the Bobacka’s group opened new opportunities for the use of ion-selective electrodes (ISEs) [1–3]. The features of the method were studied with K+ -selective ISEs as a model system [1–4]. Further studies showed that this method can be used for quantification of divalent cations Ca2+ , Pb2+ , and Cu2+ [5–7], and NO3 − , SO4 2− , and ClO4 − anions [8,9]. The main advantage of the constant potential coulometry when compared with potentiometry is its ability to register small changes of target ion concentration. The sensitivity of the traditional potentiometric measurements with ISEs is limited by the Nernst factor: RT/zI F, where R, T, and F stand for the gas constant, temperature, and the Faraday constant, while zI is the ion charge number. The constant potential coulometry method allows for overcoming this limitation
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