Design, construction and optimization studies of a hydride generation laser-induced breakdown spectrometric system, (hg-libes), for the determination of toxic elements in aqueous samples

Abstract

In this thesis study, design, construction and optimization of a continuous flow hydride generation laser-induced breakdown spectroscopic system, HG-LIBS, for the determination toxic and environmentally important elements: arsenic, selenium, lead, antimony, tin, bismuth, germanium and tellurium, has been performed. The HG-LIBS system, which has been constructed from its commercially available components, consisted of four main parts: a laser source, a hydride generation unit, a sample/plasma cell and a detection unit. In order to maximize LIBS emission signal, some instrumental parameters such as laser energy and detector gating parameters were investigated. Some chemical parameters such as acid/reductant concentration and flow rate, carrier gas type and flow rate, presence of pre-reducing/oxidizing agent that effect hydride generation efficiency and transportation of hydrides were also studied. Under optimized conditions detection limits of 0.2 mg L-1, 1.1 mg L-1, 1.0 mg L-1, 1.3 mg L-1 and 0.2 mg L-1 were obtained for Sn, As, Sb, Pb and Ge, respectively. No analytical signal could be detected from Se and Te elements with the system developed. The applicability of the HG-LIBS system for the determination of As, Sb, Pb and Ge in aqueous environments has been tested on several real water samples including tap water, drinking water and reference river water standard. Temporal variation of electron temperature and electron density values for tin and germanium hydride plasma was determined under argon and nitrogen environment. Electron temperatures were calculated by making use of neutral atomic lines in Boltzmann equation. Plasma electron density was evaluated from the Stark-broadened line shapes of Hα line at 656.3 nm. In order to investigate the main cause of increase in germanium signal under argon environment, physical plasma parameters were evaluated in argon and nitrogen gas mixtures. With this thesis study, the applicability of the HG-LIBS system for on-line monitoring of environmental pollutants has been shown.