The Research And Application Of Electrochemical Hydride Generation

Based on a detailed review on the theory and application of hydride generation-atomic spectroscopy (HG-AS) and discussion of some problems existed in electrochemical hydride generation (EcHG), systematic research was carried out, centering on the application of EcHG in atomic fluorescence spectroscopy (AFS). Two novel electrolytic cells have been designed and some materials like graphite tube and tungsten filament were firstly used as the cathode. Systematic researches of effects of catholyte on the electrolytic efficiency, elements and oxidation state were curried out and the problem of coupling AFS with EcHG was resolved. Besides, we studied the electrolytic conditions of As, Sb, Se, Ge and utilized EcHG-AFS to detect these elements in some biologic and environmental samples. The details are listed as following:We improved the traditional thin-layer cell. The problem of leakage of cell, usually existed in the traditional sealing method by screw, was resolved by the utilization of new sealing method with screw thread. A new disk electrolytic cell was designed. This newly devised disk hydride generator was constructed from a flowing electrolytic cell, in which the tungsten wire was selected as cathode. Compared with some cathode material usually used in electrochemical hydride generator, the tungsten cathode was of better interference tolerance, corrosion-resistant and longer working time. Moreover, we found the bubbles formed in net-shaped electrode cell were very small which was good for the flowing stability of solution. A common graphite tube, which has larger surface, higher hydrogen overvoltage and inertness to the electrolytes, was firstly used as the cathode for designing a compact, efficient and easy-to-operate EcHG cell. This tubular cell with a screw cape can be easily assembled, replaced and rinsed for maintaininggood experimental conditions.We studied the effects of some neutrual catholytes on EcHG. The effects of pH on the hydregon overvoltage and hydride efficiency were studie in detail. It was foundthat the use of neutral phosphate buffer solution as the electrolyte could markedly increase the hydrogen overvoltage of cathode. The fluorescence intensity of As (III) and Sb (III) increased obviously in phosphate buffer solution, however, the fluorescence intensity of As (V) and Sb (V) almost totally were suppressed. In addition, the neutral electrolyte reduced the self-erodible effect on cathode and prolonged its life time. So, we put forward a new opinion that the EcHG process could be carried out in neutral buffer solutions.We also studied the effect of mixed catholyte on EcHG and found that fluorescence intensity of As was increased obviously in the mixture solution of K₂SO₄ and ZnSO₄. The fluorescence intensity of As in acidic catholyte was the same as that in salt catholyte. Deposition of Zn²⁺ on the electrode surface enlarged the surface areas of cathode and provided a means of continuous generation of nascent hydrogen atoms deposited As to form arsine.The formation mechanism of arsine and stibine during the electrochemical reduction of aqueous arsenic and antimony solution on the Pb cathode has been investigated. The effects of current density, surface area of cathode, and flow rate of sample, concentration of analyte, hydrogen overvoltage of cathode and pH of solution on the hydride forming process were studied. The rate determining step of arsine forming reaction is the inelastic collision between the AsH and AsH₂ in acidic, neutral and alkaline solution. However, the rate determining step of stibine forming reaction in alkaline solution is the desorption of SbH₃.The EcHG-AFS technology has been applied to the determination of concentration of As, Sb, Se and Ge in biological and environmental samples inculding tobacco, tea, herb, fish and water. The accuracy and sensitivity of this technology was validated by analysing reference materials.