RESPONSE OF COPPER(II) ION-SELECTIVE ELECTRODES IN SEAWATER

A comparison of the behavior of three types of Cu(II) ion-selective electrode (i.e., copper sulfide, copper selenide, and copper/silver sulfide) in seawater has been undertaken. X-ray photoelectron spectroscopy and X-ray diffraction have shown that the unacceptably high detection limit of the CuS electrode (similar to 10(4) M Cu2+) is due to membrane oxidation to CuSO4 and Cu-3(SO4)(OH)(4). Bare Cu1.8Se and CuS/Ag2S electrodes displayed Nernstian response (i.e., similar to 100% Nernstian slope) in the range 10(-16)-10(-8) M free Cu(II) with Cu(II)-ethylenediamine buffers also containing 0.6 M NaCl. It is proposed that amelioration of the chloride interference at low levels of free Cu(II) (i,e., < 10(-8) M) is due to kinetic limitations of the membrane reaction that is responsible for the chloride interference. Corrosion of the Cu1.8Se electrode contaminated seawater with a high level of Cu(II) (similar to 100 nM), while the CuS/Ag2S electrode released a much lower amount of Cu(II) ( similar to 2.4 nM). Electrode carryover and contamination of seawater by adsorbed free Cu(II) is minimized by equilibration of the electrode in a sacrificial Cu(II) buffer (i.e., pCu(free) = 15) before analysis. The behavior of Cu(II) electrodes in seawater has been interpreted in relation to free Cu(II) levels, and results indicate a proportionality between free Cu(II) and the electrode potential.