The influence of diffusion fluxes on the detection limit of the jalpaite copper ion-selective electrode

It has been suggested that electrode dissolution and the concomitant saturation of the electrode's diffusion layer restricts the detection limit of the jalpaite Cu ion-selective electrode (ISE) to samples with total Cu levels above 10(-6) mol dm(-3) [1, 2]. This article will use rotating disk electrode (RDE) data for San Diego Bay seawater and Fick's law of diffusion to demonstrate that the static commercial Orion Cu ISE (employing a jalpaite membrane) produces a background level of contamination of (2.0 +/- 0.5) x 10(-8) mol dm(-3) total Cu, and the reduced thickness of the Orion Cu ISE's diffusion layer in the presence of hydrodynamic flow [e.g., at an RDE, or in continuous flow analysis (CFA)] lowers the background contamination of Cu to <10(-9) mol dm(-3). Furthermore, the RDE Cu ISE employing an electrode fabricated using jalpaite precipitated in 80% excess Na2S, so as to minimize the presence of occluded and leachable Cu2+ salts and extraneous phases such as silver sulfide [3 - 5], reveals an improvement in the lower limit of detection compared to the commercial Orion Cu ISE.