Potentiometric determination of cadmium using coated platinum and PVC membrane sensors based on N,N′-bis(salicylaldehyde)phenylenediamine (salophen)

The construction and performance characteristics of novel PVC membrane (PME) and coated platinum (CPtE) cadmium ion selective electrodes based on N,N′-bis(salicylaldehyde)phenylenediamine (salophen) are described. The electrodes exhibit linear responses along with near Nernstian slopes of 28.9 ± 0.4 (PME) and 29.2 ± 0.6 (CPtE) mV/decade of concentration within the Cd2+ ion concentration range of 5.7 × 10−8 to 3.7 × 10−3 M for PME and 3.0 × 10−8–3.0 × 10−3 M for CPtE. These sensors are applicable in a pH range of 2.5–7.5. The lower detection limits by PME and CPtE are 3.2 × 10−8 and 1.6 × 10−8 M, respectively. They have a response time less than 14 s and can be used practically for a period of at least 2 months without any measurable divergence in results. The electrode can also tolerate partially non-aqueous media (ethanol, methanol and acetone) up to 30%. The electrodes showed excellent selectivity towards Cd2+ ion over a wide range of alkali, alkaline earth, and transition metals ions. They were successfully applied to the direct determination of Cd2+ ions in tap water, aqueduct water, and river water and soil sample. In addition the electrodes were used as an indicator electrode in potentiometric titration of Cd2+ ion with EDTA.