Highly Sensitive Detection of Lead in Aqueous Solution using Laser-Induced Breakdown Spectroscopy Coupled with Adsorption Technique

Abstract

Two types of adsorbents, zinc oxide (ZnO) and zeolite, have been used to probe the lowest detectable limit of lead (Pb) dissolved in water. To achieve the goal, water-soluble Pb complexes were produced by dissolving in water or titrating with HNO3 acid with different concentrations of four different compounds of Pb. The dissolved Pb complexes were then allowed to be adsorbed onto ZnO or zeolite. LIBS spectra of the Pb–ZnO and Pb–zeolite composites were recorded in the 331.5–370.5, and 355–394 nm spectral windows, respectively. Calibration curves were drawn using the normalized line intensities of Pb I at wavelengths of 357.269, 363.958, and 368.319 nm versus the concentration of the added Pb. For all the adsorbates (the Pb compounds) used, the adsorption curves as a function of the adsorbate concentration in water followed the Langmuir type isotherms. The lowest limit of detection (LoD) and the slope of the linear part of the adsorption isotherm varied for various adsorbents, adsorbates, and different Pb I emission lines used. ZnO was found to be a better adsorbent than zeolite in terms of LoD and the slope of the linear part of the isotherm and hence the sensitivity of the detection. The LoD for Pb in an aqueous solution in the current LIBS experiment coupled with the adsorption technique was found to be 0.5 ppm.