Fabrication of novel coated graphite electrodes for the selective nano-level determination of Cd2+ ions in biological and environmental samples

Novel cadmium selective coated graphite electrodes were prepared using three different ionophores N1, N2-dicyanoethyl-N1, N2-bis(pyridin-2-ylmethyl)benzene-1, 2-diamine [L1], N1, N2-dicyanoethyl-N1, N2-bis(thiophen-2-ylmethyl) benzene-1, 2-diamine [L2] and N1, N2-dicyanoethyl-N1, N2-bis(furan-2-ylmethyl)benzene-1, 2-diamine [L3], and their potentiometric characteristics were determined. Membranes having different compositions of poly(vinylchloride) (PVC), the plasticizer o-nitrophenyloctylether (o-NPOE), sodium tetraphenylborate (NaTPB) as an anionic additive and ionophores were coated onto the graphite surface. The potential response measurements showed that the best performance was exhibited by the electrodes with membranes having the composition L1: o-NPOE:NaTPB:PVC as 4:51:2.5:42.5 (wt.%), L2: o-NPOE:NaTPB:PVC as 3:52.5:1.5:43 (wt.%) and L3: o-NPOE:NaTPB:PVC as 7:49:3.5:40.5 (wt.%). These electrodes had the widest working concentration range, Nernstian slope and fast response times of 12 s, 7 s and 17 s for L1, L2 and L3, respectively. The selectivity studies showed that these electrodes have higher selectivity towards Cd2+ over a large number of cations and could tolerate up to 20 vol.% non-aqueous impurities. Furthermore, the electrodes generated constant potentials in the pH range 2.0-8.0, with a shelf life of approximately four to six weeks. The high selectivity of these electrodes permits their use in the detection of the Cd2+ content in some medicinal plants, soil and industrial wastewater samples. The electrodes could also be used as an indicator electrode in the potentiometric titration of Cd2+ with EDTA.