Development of a highly sensitive and selective optical chemical sensor for batch and flow-through determination of mercury ion

A very sensitive, highly selective and reversible optical chemical sensor (optode) for mercury ion is described. The sensor is based on the interaction of Hg²⁺ with 2-mercapto-2-thiazoline (MTZ) in plasticized PVC membrane incorporating a proton-selective chromoionophore (ETH5294) and lipophilic anionic sites (sodium tetraphenylborate, NaTPB). The membranes were cast onto glass substrates and used for the determination of mercury ion in aqueous solutions by batch and flow-through methods. The sensor could be used in the range 2.0 × 10⁻¹⁰ to 1.5 × 10⁻⁵ M (0.04 ng mL⁻¹ to 3 μg mL⁻¹) Hg²⁺ with a detection limit of 5.0 × 10⁻¹¹ M and a response time of <40 s. It can be easily and completely regenerated by dilute nitric acid solution. The sensor has been incorporated into a home-made flow-through cell for determination of mercury ion in flowing streams with improved sensitivity, precision and detection limit. The sensor showed excellent selectivity for Hg²⁺ with respect to several common alkali, alkaline earth and transition metal ions. The results obtained for the determination of mercury ion in river water samples using the proposed optode was found to be comparable with the well-established cold-vapor atomic absorption method.