Ultratrace determination of cadmium ion in petrochemical sample by a new modified carbon paste electrode as voltammetric sensor

A novel chemically modified carbon paste electrode (CMCPE) impregnated with 4′-(4-chlorophenyl)-2,2′:6′,2′′-terpyridine ligand was prepared and applied for voltammetric determination of Cd^2+ ion in petrochemical samples. The effects of pH, ligand amount and supporting electrolyte on the selective adsorption properties for the Cd^2+ ion were explored. The sensor displayed substantially good resistance against interfering agents. In the presence of a large excess of Na^+, K^+, Ca^2+, Mg^2+ and Pb^2+, the adsorption capacity for Cd^2+ was slightly changed, suggesting the high selectivity of CMCPE for Cd^2+ions. The parameters controlling the response of the electrode were investigated. The limit of detection (LOD) and relative standard deviation (n = 5) were obtained by 3.77 ng/L and 0.45%, respectively. The preconcentration procedure revealed a linear curve within the concentration range of 4 – 3000 ng/L and a good linearity with squared correlation coefficient of (R^2) 0.9988 was achieved. The CV was run starting from –1.5 V to 0.0 V and back (Scan rate: 100 mV/s). The best ratio of the Cd^2+-Ligand in carbon paste was 8% (w/w) for a good detection of C^d2+ ions. Optimum pH for maximum adsorption was 4.0 ±0.2. All the instrumental parameters involved in the analytical procedure were optimized. The study was accomplished in Britton–Robinson (B-R) buffer solution of 2 ng/mL Cd^2+ ions. The optimal values of scan rate, pulse amplitude, pulse time, voltage step, voltage step time, deposition potential and deposition time were obtained 100 mV/s, 0.20 V, 0.04 s, 0.005 V, 1.2 s, – 0.95 V and 150 s, respectively.