Development of highly sensitive cadmium ion-selective electrodes by titration method and its application to cadmium ion determination in industrial waste water

Characteristics of cadmium ion-selective electrode made cadmium sulphide (CdS)-silver sulphide (Ag2S) mixture were studied. CdS-Ag2S mixtures were obtained by gas/solid-phase reaction between silver-cadmium mixed powder and hydrogen sulphide gas (dry method) and by ionic reaction between cadmium-silver mixed ions and sulphide ion (wet method). As a result, it was found that the CdS-Ag2S mixture had to be made in the condition of excess existence of sulfur and had better regulate the excess sulfur quantity minimum, for the CdS-Ag2S pressed membrane gave a good Nernstian response against the cadmium ion concentration change. As the best way, CdS-Ag2S mixture was obtained by adding sulphide ion solution to 5 mol% cadmium ion and 95 mol% silver ion mixed solution while measuring silver sulphide (Ag2S) electrode potential as an indicator electrode. According to the reaction was stopped when the potential variation from the initial potential in the sulphide ion solution reached at 87-116 mV which the sulphide ion concentration became 10(-3)-10(-4) of the initial concentration, the cadmium ion membrane pressed diameter of 8 mm and thickness of 2 mm showed a Nernstian response from 10(-8) to 10(-1) M of cadmium ion concentration, Furthermore, aiming to its application for industrial waste water, masking buffer for interfering metal ions such as lead ion (Pb2+) and copper ion (Cu2+), which were possibly coexisted and to adjust total ionic strength and pH of sample was developed. The present Cd2+ ion-selective electrode was applied to the determination of Cd2+ in the industrial waste water. The good regression line with correlation factor of 0.984 was obtained compared with the conventional atomic absorption spectroscopy. (C) 1997 Elsevier Science B.V.