The parameters optimization of the square wave voltammetry applied to Cd detection using doped diamond electrodes with different doping levels

Full text: Monitoring heavy metal ion levels in water is essential for human health and safety. There are numerous health problems associated with exposure to high levels of heavy metal ions because of their tendency to accumulate in the body, toxicity and low rate of clearance. Electroanalytical techniques have presented important features to detect toxic trace metals in the environmental due to their high sensitivity associated to their easy operational procedures. In this way, boron doped diamond (BDD) appears as alternative material to use in mercury-free analytical systems [1,2]. Thus, in this work we investigated the parameters optimization of square-wave anodic stripping voltammetry (SWASV) using BDD becomes a very attractive subject mainly for electrodes with different doping levels. The cadmium detection was investigated considering the optimized relation among the peak current associated to the pulse frequency, the amplitude and the potential increment for highly (10¹⁹ cm^-3) and heavy doped BDD (10²¹ cm^-3) electrodes. The films were grown in a hot filament by chemical vapor deposition technique on Si substrate using H₂/CH₄ (99:1). Boron was obtained from an additional H₂ line passing through a bubbler containing trimethyl borate [(CH3O)₃B] dissolved in methanol with dissolution of 2000 and 20000 ppm of B/C. The films were characterized by Scanning Electron Microscopy, Raman spectroscopy, X-ray diffraction and Mott-Schotkky Plots to evaluate the acceptor concentrations in such films. The analysis of Cd²⁺ were performed using SWASV technique in 0.1 mol.L^-1 acetate buffer pH 4.0 after purging nitrogen for 5 min following different steps: (a) pre-conditioning step applying the potential of 0.9 V vs. Ag/AgCl for 45 s before each measurement to ensure the dissolution of the remaining deposits on the electrode surface; (b) the pre-concentration step procedure at -1.2 V vs. Ag/AgCl for 90 s; and (c) the SWASV voltammograms recorded from −0.8 V to 0.0 V. The peak currents around -0.75 V vs. Ag/AgCl for Cd²⁺ concentration ranged from 1 to 100 ppb were measured. Overall, the detection figures of merit for BDD are as good or superior to those for Hg. Both BDD and Hg provided detection limits for all the metal ions in the mid to low ppb range showing that diamond electrodes are a suitable mercury-free method to determine cadmium trace levels in water. References: [1] E.C. Almeida, A. F. Azevedo, M. R. Baldan, J. M. Rosolen, N. G. Ferreira, Chem. Phys. Let, 438 (2007) 47. [2] E. A. McGaw, G. M. Swain , Anal. Chim. Act. 575 (2006) 180-189. (author)