Voltammetric studies of lead at calixarene modified screen-printed carbon electrodes and its trace determination in water by stripping voltammetry

Screen-printed carbon electrodes (SPCEs) have been modified with two different calixarenes; a novel thiolated calixarene (5,11,17,23,tetra-tert-butyl-25,26,27,28-tetrakis(2-mercaptoethoxy)-calix[4]arene), and the commercially available 25,26,27,28-tetrahydroxy-calix[4]arene. Both calixarene modified SPCEs (CAL-SPCEs) were evaluated for the trace determination of lead ions (Pb2+). Pb2+ were accumulated from ammonia buffer, on the CAL-SPCE surface by the formation of a chemical complex at open circuit. The resulting SPCE with complexed Pb2+ was then transferred to 0.1 M HCl and subjected to cyclic voltammetry to investigate the nature of the accumulation process. Further investigations were undertaken using differential pulse anodic stripping voltammetry (DPASV). Conditions were optimised with respect to the pH and concentration of the accumulation medium, preconcentration time and the mass of drop-coated calixarene. The thiolated calixarene was found superior in terms of sensitivity and further investigations were carried out on this CAL-SPCE. A 10 min preconcentration time, followed by DPASV resulted in a limit of detection of 5 ng ml−1, with a linear range to 100 ng ml−1 Pb2+. The method was evaluated by carrying out lead determinations on spiked river water samples at 14 ng ml−1; the mean recovery of Pb2+ was 95.9% and the coefficient of variation was found to be 8.4% (n=5) using a separate CAL-SPCE for each determination. Therefore, the performance data suggests that the method is reliable at the concentrations examined in this study.