A PVC-based capric acid membrane potentiometric sensor for lead(II) ions

Four different fatty acids (C7, C10, C14, and C18) were studied to characterize their abilities as lead(II) ion carrier in PVC membrane electrodes. The electrode based on capric acid [CH3(CH2)8COOH] shows good Nernestian response for Pb2+ ions. The optimum composition of the membrane was 30 wt.% poly(vinyl chloride), 60 wt.% NPOE as plasticizer, 5 wt.% ionophore, and 5 wt.% potassium tetrakis (p-chlorophenyl) borate as lipophilic salt. The electrode exhibits a Nernstian slope of 29.0±0.5 mV per decade for Pb2+ over a wide concentration range (1.0×10−5–1.0×10−2). It can be used for a period of 3 months without any considerable divergence in potentials. The proposed electrode revealed good selectivities for Pb2+ over a wide variety of other metal ions and could be used in the pH range of 4.5–7. It shows a good stability, good reproducibility, and fast response. The electrode was used for the potentiometric titration of chromate ions with lead ions.