The use of membrane electrodes in the determination of sulphides in sea water

The direct potentiometric determination of sulphides in natural sea water with a sulphide-selective membrane electrode is proposed. The experimental evaluation of the “apparent mixed” dissociation constants and the thermodynamic activity coefficient in spiked sea water samples, by means of the electrode, permits direct calibration in terms of activity. Alternatively, it is possible to establish, for natural sea water, an experimental equation for the correction of the electrode potentials in terms of pH; this allows direct calibration of the electrodes in terms of total sulphide concentration. This criterion can be applied to any aqueous solution.