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. (C) 2001 Elsevier Science B.V. All rights reserved.