Abstract: This work describes the development of an instrument for measuring free and total copper in seawater by continuous flow analysis (CFA) with an Orion copper(II) ion selective electrode (CuISE). Sample analysis times are reduced considerably by using an extrapolation technique based on the fitting of an empirical mathematical expression to the electrode time-response curve enabling a prediction of the final equilibrium potential. CuISE measurements in seawater samples containing nanomolar levels of total copper can be very time consuming, and this predictive approach significantly reduces sample analysis time, and improves sample throughput. The time taken to measure pCu in seawater to a precision of±0.1, using conventional potentiometry, varies considerably depending on the condition of the electrode membrane but can be reduced by a factor of 3-6 (typically from 60 to 10 min) by using the extrapolation technique in conjunction with CFA. Details are given of the protocols used for preconditioning the CuISE. The system can be used as a portable instrument for field measurements or for shipboard measurements of free copper in seawater. Extrapolated equilibrium potentials are within±0.5 mV of true steady state values.

Abstract: The fluoride ion-selective electrode has been used in continuous flow analysis to determine the fluoride concentration in aqueous solution. The varying electrode potentials, E(t), were collected in the first 60 s by an interfacing computer, and the equilibrium potential of the electrode was predicted using an extrapolation method. This value agrees to within ±0.5 mV of the comparative value obtained by allowing sufficient time for the electrode to reach a steady state. Like flow-injection (FI), continuous flow (CF) analysis with this extrapolation method significantly shortens the time required for routine fluoride concentration measurements, but it also achieves a higher sensitivity than FI. The method has been applied to the determination of fluoride in city tap water.