VOLTAMMETRIC DETERMINATION OF LEAD WITH A CHEMICALLY-MODIFIED CARBON-PASTE ELECTRODE WITH DIPHENYLTHIOCARBAZONE

A carbon paste electrode modified with dithizone (diphenylthiocarbazone) was employed for quantification of lead from aqueous solutions. Lead(II) was chemically deposited on the chemically modified electrode (CME) by complexation with the modifier, and the electrode was transferred to an electrochemical cell for pulse voltammetric anodic stripping. The response depends on the concentration of lead in the bulk solution as well as the parameters involved in both the preconcentration and the measurement steps. For a 6-min preconcentration time, the calibration graph is linear from 20.7 ng ml(-1) to 207.2 ng ml(-1) and from 207.2 ng ml(-1) to 518.0 ng ml(-1). The detection limit (DL, 3 sigma) was about 16.7 ng ml(-1) and the response could be reproduced with a 5.8% relative standard deviation at the concentration level of 31.1 ng ml-l. Interferences by metal ions which compete for complexation with the modifier on the CME surface could be eliminated by using masking reagents. Strong complexing agents, such as sulphide, interfere. The method was used for the determination of lead in natural waters.