Square Wave Voltammetric Determination of Lead(II) Ions Using a Carbon Paste Electrode Modified by a Thiol-Functionalized Kaolinite

This work reports the electroanalysis of lead(II) in aqueous medium, using a carbon paste electrode modified by a novel thiol-functionalized clay. This later was obtained upon the grafting of 3-chloropropyltriethoxysilane onto the interlayer surfaces of kaolinite, followed by the substitution under carefully controlled conditions of chloro by thiol groups. The raw kaolinite, its dimethylsulfoxide (DMSO) intercalate used as starting material and the resulting hybrids were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy and CHNS elemental analysis. These techniques demonstrated the displacement of DMSO by the organosilane molecules which were grafted on the internal hydroxyl groups located on the kaolinite surface. The final functionalized kaolinite, with approximate chemical formula Si4Al4O10(OH)(6)[O2Si(OEt)(CH2)(3)SH] was evaluated as electrode modifier for lead(II) sensing. A two-step analytical procedure based on the accumulation at open circuit-detection was applied by square wave voltammetry. Various parameters affecting both the two steps were optimized: a linear response to lead(II) was obtained in the concentration range from 3 x 10(-7) to 10(-5) M, with a detection limit estimated at 6 x 10(-8) M. The interfering effect of some ions likely to influence the stripping determination of lead(II) ions was evaluated, and the proposed method applied to a real sample.