Chelating ionophores based electrochemical sensor for Hg(II) ions

Poly(vinyl chloride) (PVC)-based membranes of pyrimidines, 1-(2′-aminoaryl)-4, 4, 6-trimethyl-1, 4, 5, 6-tetrahydro-6-hydroxypyrimidine-2-thiol (HPT) (R = −H, −CH₃, −OCH₃) with sodium tetraphenylborate (NaTPB) as an anion inhibitor and dibutylphthalate (DBP), dioctylphthalate (DOP), dibutyl (butyl) phosphonate (DBBP) and 1-chloro naphthalene (CN) as plasticizing solvent mediators were prepared and used as Hg²⁺ selective electrodes. Optimum performance was observed with the membrane having HPT(−OCH₃)−PVC−NaTPB−DOP in the ratio 1:33:1:65 (w/w). The electrode works well over a wide concentration range 5.0 × 10⁻⁶−1.0 × 10⁻¹ M (detection limit 1.0 ppm) with Nernstian compliance (29.5 mV decade⁻¹) between pH 2.5 and 4.0 with a fast response time of about 20 s. The selectivity coefficient values of the order of 0.001 for mono-, bi- and trivalent cations, indicate high selectivity for Hg²⁺ ions over these cations. Further, anions such as Cl⁻ and SO ₄ ²⁻ do not interfere in the functioning of Hg²⁺ sensor. The electrodes were used over a period of five months with good reproducibility (std. dev. ±0.2 mV) and the performance of the electrodes was found satisfactory even up to 10% nonaqueous medium. The electrode assembly was also evaluated for potentiometric determination of Hg²⁺.