A comparative study on carbon paste electrodes modified with hybrid mesoporous materials for voltammetric analysis of lead (II)

We have chemically functionalized four types of ordered mesoporous silicas (referred to as MPS1–MPS4) with 5-mercapto-1-methyltetrazole (MTTZ), and have incorporated these materials into carbon paste electrodes (CPEs) to obtain sensors for the determination of Pb(II) ion in aqueous media by adsorptive stripping voltammetry. Materials and MPS1–MPS4, were characterized by nitrogen adsorption–desorption measurements, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and elemental analysis. The effect of the mesostructure of the MPS on the performance of the sensors was evaluated with respect to linear ranges, sensitivities, selectivities, precision and limits of detection. The CPE modified with MPS1 (a silica with mesopores of 37 Å in diameter and pseudo-spherical particle morphology) exhibited the best inter-electrode reproducibility and sensitivity, a linear range between 1 and 30 ppb and a limit of detection of 0.8 ppb. The CPE modified with MPS4 (a silica with hexagonal mesopores of 58 Å in diameter, cylindrical particle morphology and bigger size) exhibited the poorest inter-electrode reproducibility and sensitivity, a linear range between 5 and 100 ppb, and a limit of detection of 2.6 ppb. The differences in the voltammetric responses to Pb(II) therefore appear to result from differences in the coating of the inner surface with MTTZ, the pore diameter, and the particle morphology as well as the size of the hybrid MPS. As consequence of its highest inter-electrode reproducibility and sensitivity, good linear range and low limit of detection, MPS1 can be selected as the better material to prepare modified CPE for Pb(II) determination in aqueous media by adsorptive stripping voltammetry.