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 stud ied using up to 5 similar Orion 90-24, jalpaite-based electrodes. Larg e variability (ca. 1 pCu unit) among the values yielded by the individ ual electrodes was observed when the electrodes were stored in artific ial seawater and exposed to light including sunlight This variability is in agreement with mechanisms proposed previously. The variability a mong the electrodes was reduced to about +/-0.2 pCu units when the ele ctrodes were stored in sacrificial EN seawater solution and shielded f rom light. Eight measurements of San Diego Bay seawater made with an i ndividual electrode yielded pCu = 12.23 +/-:0.06 (1 sigma) regardless of the order in which the electrode was calibrated with standard buffe r solutions. This degree of precision makes it possible to follow the small, time-dependent changes in the pCu of seawater. The effects of e lectrode rotation and the adsorption or desorption of organic matter o n the electrode are presented and discussed. (C) 1998 Elsevier Science B.V. All rights reserved.