Studies On Gas-Phase Chemiluminescence Following Flow Injection Hydride Generation And Its Application On Environmental Analysis

It is of great importance to develop analytical methods for the determination of pollutants in environmental samples. The methods should be characterized by accuracy, high sample throughput, high sensitivity and good selectivity in order to be applied to the analysis of samples with low concentration and complicated matrix.Chemiluminescence is the emission of light as the result of a chemical reaction without the excitation by light, electricity, magnetic force, sound and heat. It is an attractive detection technique for environmental analysis because of its very low detection limit, rapidity and wide linear working range that can be achieved while using relatively simple instrumentation.Flow injection analysis （FIA） is a non-chromatographic flow analysis technique that can manipulate reproducibly sample and reagent zones in a flow stream through precise timing. Fast and automatic analysis can be conducted with excellent reproducibility and low consumption of sample and reagents. The analytical performance can be enhanced significantly when FIA is integrated into chemiluminescence analysis.In the present dissertation, new methods are developed for the determination of trace amount of hydride-forming elements including antimony, tin and selenium in environmental samples. The methods are based on gas-phase chemiluminescence （GPCL） from the oxidation of gaseous hydrides by ozone. FIA is used to generate hydrides followed by their separation and preconcentration.The major contents in this dissertation are described as follows.Chapter One A brief review is given on the mechanisms, typical reaction systems and applications of chemiluminescence analysis, and the principle mechanisms, characteristics and applications of flow injection technique. Their applications and development trends in environmental analysis are also presented. The research topics of this dissertation are thus proposed.Chapter Two A systematic study is conducted on the analytical characteristics of GPCL for the hydride-forming elements by optimizing the experimental conditions. It provides the basis for GPCL to be applied to the analysis of environmental samples. The results show that the sensitivities of As, Sb, Sn and Se are relatively high and GPCL may be used for their analysis in environmental samples potentially.Chapter Three A novel method is developed for the determination of trace tin in environmental samples based on ozonization of stannane. Excellent detection limit is achieved by the preconcentration of stannane using cryotrapping after its generation with FIA. Interferences from other hydride forming elements are minimized by controlling the acidity for hydride generation. Interferences from transition elements are alleviated with the addition of masking agent into the samples. The developed method is characterized by simplicity and high sensitivity with a wide linear working range of 2.0 to 10000μg L^-1 and a low detection limit of 0.32μg L^-1. It is successfully applied to the determination of tin in environmental samples with satisfactory results.Chapter Four A novel method for the determination of antimony in environmental samples is developed with GPCL detection following flow injection hydride generation and cryotrapping. The stibine, generated from samples by borohydride reduction of Sb using flow injection technique, is separated and concentrated in a glass U-tube immersed in liquid nitrogen. Re-vaporization of stibine is achieved by allowing the tube to warm at room temperature. A GPCL signal is produced during the ozonation of the hydride in a reflective chamber. Interferences from other hydride-forming elements are eliminated with sequential re-vaporization based on their different boiling points. The developed method is characterized by high sensitivity with a wide linear working range of 1 to 10000μg L^-1 and a low detection limit of 0.18μg L^-1. It is applied successfully to the analysis of Sb in environmental samples.Chapter Five The GPCL detection system based on the ozonation of gaseous hydride is further exploited and utilized for the measurement of trace selenium in environmental samples. Selenium is separated from the matrix by the formation of piazselenol using 4-nitro-o-phenylenediamine as derivative agent. The generated piazeselenol is decomposed into Se（Ⅵ） with the action of persulfate photocatalytic oxidation. Se（Ⅵ） is reduced Se（Ⅳ） in boiling water with HCl and KBr. Hydrogen selenide is generated by Se（Ⅳ） under the reduction of sodium borohydride and measured with gas phase chemiluminescence detector. The developed method is characterized by a wide linear calibration range from 0.5μg L^-1 to 1.0 mg L^-1,with a detection limit of 0.12μg L^-1. It is applied to the determination of trace selenium in environmental samples with satisfactory results.Chapter Six Gas chromatography is used to separate the hydrides of arsenic, antimony, tin and selenium after their generation using FIA technique. Chemiluminescence is produced when the separated hydrides react with ozone and detected by the luminescence detector. Mutual interferences are therefore eliminated due to the chromatographic separation with a Tenax TA column. Under the optimized conditions, linear relationships are obtained for As, Sb, Sn and Se in the range of 1μg L^-125 mg L^-1, 0.4⁴0 mg L^-1, 0.1³0 mg L^-1 and 0.5⁵0 mgL^-1 respectively. The detection limits for As, Sb, Sn and Se are 0.28μg L^-1, 0.12 mgL^-1, 0.035 mg L^-1 and 0.16 mg L^-1, respectively. Yet, the developed method suffers from its poor sensitivity caused by the diffusion of the hydrides occurred during the repeated process of adsorption and desorption in the column. Measures should be taken to improve the sensitivity so that it may be used for environmental analysis.