Modified Carbon Paste Electrode for Pb2+ Ion Determination: Response Surface Methodology

A novel carbon paste electrode (CPE) based on 2,2´(ethane 1,2-diylbis (azanylylidene)) bis (ethan-1-yl-1-ylidene)) diphenol (L) was prepared for selective determination of trace amount of Pb²⁺ ion. The effects of individual variables, such as amounts of L, sodium tetraphenylborate (NaTPB), graphite powder, and Nujol as well as their possible interactions were investigated and optimized using central composite design under response surface methodology. Optimum composition of carbon paste was set as 100-mg Nujol and the mass (milligram) ratio of 209/4/6 for graphite powder: NaTPB: carrier, respectively. Such composition was found to be led to significant enhancement in the selectivity and sensitivity of the CPE toward Pb²⁺ ions over a wide concentration range of 3.7 × 10^-7 -1 × 10^-2 mol L-1 with detection limit of 1.5 × 10^-7 mol L^-1 and a Nernstian slope of 30.7±1.56 mV/decade of Pb²⁺ concentration. Negligible significant change in response was seen over wide pH range of 4-6 with response time lower than 14 s. The good selectivity of the CPE for Pb²⁺ ion toward other metal ions was confirmed by the potentiometric selectivity coefficients. Finally, to be practical, these electrodes were accurately and repeatability used for the determination of Pb²⁺ ions in real water sample.