Comparative studies of tridentate sulfur and nitrogen-containing ligands as Ionophores for construction of cadmium ion-selective membrane sensors

New polymeric membrane cadmium-ion selective sensors have been prepared by incorporating nitrogen and sulfur containing tridentate ligands as the ionophores into the plasticized PVC membranes. Poly(vinyl chloride) (PVC) based membranes of potassium hydrotris[N-(2,6-xylyl)thioimdazolyl) borate] (KTt(2.6-xylyl)) and potassium hydrotris(3-phenyl-5-methylpyrazolyl) borate (KTp(ph,Me)) with sodium tetraphenyl borate (NaTPB) as an anionic excluder and dibutylphthalate (DBP), tributylphthalate (TBP), dioctylsebacate (DOS), and o-nitrophenyloctyl ether (o-NPOE) as plasticizing solvent mediators were investigated in different compositions. KTt(2,6-xylyl) was found to be a selective and sensitive ion carrier for Cd(II) membrane sensor. A membrane composed of KTt(2,6-xylyl) :NaTPB:PVC:DBP with the % mole ratio 2.3:1.1:34.8:61.8 (w/w) works well over a very wide concentration range (7.8 x 10(-8)- 1.0 x 10(-2) M) with a Nernstian slope of 29.4 +/- 0.2 mV/decades of activity between pH values of 3.5 to 9.0 with a detection limit of 4.37 x 10(-8) M. The sensor displays very good discrimination toward Cd(II) ions with regard to most common cations. The proposed sensor shows a short response time for whole concentration range (ca. 8 s). The effects of the cationic (tetrabutylammonium chloride, TBC), anionic (sodium dodecyl sulfate, SDS) and nonionic (Triton X-100) surfactants were investigated on the potentiometric properties of proposed cadmium-selective sensor. The proposed sensor based on KTt(2,6-xylyl) ionophore has also been used for the direct determination of cadmium ions in different water samples and human urine samples.