Current pulse based ion-selective electrodes for chronopotentiometric determination of calcium in seawater

Calcium is closely related to the oceanic biosphere and carbonate system. Potentiometry based on a calcium-selective electrode (Ca-ISE) represents a promising tool for detection of calcium ion activities in seawater. This technique, however, generally is limited by the low sensitivity for the inhere...
Ausführliche Beschreibung

Calcium is closely related to the oceanic biosphere and carbonate system. Potentiometry based on a calcium-selective electrode (Ca-ISE) represents a promising tool for detection of calcium ion activities in seawater. This technique, however, generally is limited by the low sensitivity for the inherent Nernstian response (i.e. ca 30 mV/dec). A current pulse based ion-selective electrode with enhanced sensitivity for chronopotentiometric measurements of calcium in seawater is proposed. The Ca2+-selective membrane containing lipophilic salt ETH 500 instead of traditional ion-exchanger is galvanostatically controlled. An applied constant cathodic current pulse can leads to the extraction of the calcium ions into the membrane to produce a chronopotential response, which shows a stable and reproducible super-Nernstian response in a narrow calcium activity range. The super-Nernstian region of the electrode depends on not only the the magnitude and duration of the applied current pulse but also the interfering ions. Under optimal conditions, the proposed Ca-ISE exhibits a super-Nernstian response between the calcium concentrations of 10−2.5–10−1.5 M with a slope of ca 80 mV/dec. The current pulse based Ca-ISE has been applied to determination of calcium in seawater with satisfactory results. Ausführliche Beschreibung