Study On Hydride Generation Mechanism Of Elements In D Zone Of Periodic Table And Its Application To Eco-entironmental Analysis

The technique of hydride generation (chemical vapor generation) can separate the analyte from the matrix of samples by chemistry reaction, which will avoid the possible spectrum interference, and significantly improve the sensitivity of analytical procedure due to the efficiency improvement of sampling and atomization by gaseous sample introduction. It is an effective method of sample introduction to solve problems in the analysis of samples with complex matrix and speciation, which opened a new field for the work of valence state analysis, speciation analysis and enrichment. In recent years, expanding the scope of vapor (hydride) forming elements became an important research aspect in this field. Up to now, the scope has been expanded to the transition and noble elements. However, the vapor generation efficiency of the transition and noble elements are very low, and the reaction mechanism and the nature of the volatile production remain unknown. To know whether or not and how the transition and noble elements produce some volatile species by reacting with tetrahydroborate is meaningful for both the analysis method establishment of those elements (for the samples with special matrix) and the research of interference from those elements with the hydride generation of other elements. A reasonable mechanism of hydride generation via reaction with tetrahydroborate was proposed for the first time in detail, of which the volatile hydrides of metal elements were produced by the transfer of negative hydrogen from BH4- to the metal atom, rather than by the reaction of metal atom with the nascent hydrogeon. Thetransfer of negative hydrogen was accomplished by the decomposition of a transient intermediate produced by the reaction of metal ion with BH4-. Taking Zn, Cd, Cu and Ni for example, the approaches to improve the hydride generation efficiency of transition and noble metals were studied on the basis of the hydride generation mechanism proposed. As a result, the hydride generation efficiency of Zn, Cd, Cu and Ni were significantly improved by some complexes, transition metal ions and surfactants. The enhancing mechanism of these reagents was reasonably explained in view of the reaction mechanism of hydride generation. The nature of volatiles of Zn, Cd, Cu and Ni were investigated by the intermittent flow hydride generation atomic fluorescence spectrometry. It was found that the volatile species of Cd was unstable hydride CdH2 while the volatile species of Zn, Cu and Ni were stable hydride molecules presented as aerosol form in the vapor.In the application studies of hydride generation of d zone elements in periodic table, the gaseous phase enrichment techniques in hydride generation of cadmium and nickel were coupled with graphite furnace atomic absorption spectrometry. The detection method of ultra trace cadmium using hydride generation graphite furnace atomic absorption spectrometry after in situ trapping on a coated graphite tube with permanent modifier Ir was developed. The detection methods of trace nickel using hydride generation graphite furnace atomic absorption spectrometry after in situ trapping on a coated graphite tube with permanent modifier Pd/lr and trapping in 0.5 mol L-1 HNO3 solution were respectively established. The methods proposed were sensitive and simple, and successfully applied to the analysis of ultra trace cadmium and trace nickel in environmental samples...