Direct measurement of Cu(II)aq in seawater at pH 8 with the jalpaite ion-selective electrode

The variability of measurement of the pCu of seawater at pH 8 was studied using up to 5 similar Orion 90-24, jalpaite-based electrodes. Large variability (ca. 1 pCu unit) among the values yielded by the individual electrodes was observed when the electrodes were stored in artificial seawater and exposed to light including sunlight. This variability is in agreement with mechanisms proposed previously. The variability among the electrodes was reduced to about ±0.2 pCu units when the electrodes were stored in sacrificial EN seawater solution and shielded from light. Eight measurements of San Diego Bay seawater made with an individual electrode yielded pCu=12.23±0.06 (1 σ) regardless of the order in which the electrode was calibrated with standard buffer solutions. This degree of precision makes it possible to follow the small, time-dependent changes in the pCu of seawater. The effects of electrode rotation and the adsorption or desorption of organic matter on the electrode are presented and discussed.