Miniaturization Of Spectroscopic Instrumentation Based On CCD And New Chemiluminescence Techniques

Green Chemistry has aroused great interest in recent years because of its environmental and economic benefits. As a qualitative and quantitative science, analytical chemistry is not only part and parcel of Green Chemistry but also an umpire or referee for it. Thus, it requires analytical chemistry itselft to be green. Spectral analysis has some unique features, like simple mechanism as well as instrumentation and wide applications for various samples. Such advantages make spectral analysis may be the best ways towards green analytical chemistry.The components of a spectral instrument can be roughly divided into three parts: light source/excitation system, sample loading system and detection system. The improvement and development of these parts may enhance the performance of current spectroscopic instruments, and even induce the innovation of this analytical technique. All these advances may lead to the green end of spectroscopic analysis. This dissertation describes some studies on the advances of spectral analysis through two ways: one is using new atomization methods and a handheld CCD spectrtometer to develop miniaturized/portable spectroscopic instruments, the other is extending the applications of chemiluniscence (CL) analysis with new chemiluminescence methods.Atomization is no doub the most critical part for atomic spectrometry. There are many techniques to achieve the goal of atomization: arc spark, flame, electrothermal techniques plasma techniques. No matter which technique is adopted, the way to realize atomization of these techniques is by high-temperature decomposition. In order to reach the desired high decomposition temperature, some compromises (or shortcomings) are unavoidable, like bulk device, complicated instrumentation, high power requirement, carrier/combustion gas consumption, and so on. Methods that can generate free atoms in a simple and cost-efficient way, or even at ambient temperature are promising in pursuing miniaturized/portable atomic spectrometric instrument. Therefore, two atomization methods with those advantages, tungsten coil electrothermal atomization and photo-induced atomization in aqueous solution are discussed in this dissertation.As the development of the industry of semi-conductor, CCD detector becomes more and more universial in analytical instrument. A handheld CCD spectrometer (integrated with a grating and a CCD detector) is also easily available in nowadays, which can be used to develop miniaturized/portable instrument. Although the sensitivity of the handheld CCD spectrometer is not comparable to a photomultiplier tube (PMT), its compact size, multi-channel nature, long continuous working time and energy-saving capabilities of the CCD spectrometer make it more suitable for miniaturized/potable analytical instrumentation, continuous multi-component analysis as well as field/on-site monitoring. The first three work of this dissertation all employed a handheld CCD spectrometer as the detector.The most extraordinary characteristics of CL analysis are of its low or even no background and high sensitivity. Its high sensitive, selectivity, rapidity, simplicity and low cost of instrumentation make it become a popular analytical method. The drawback of conventional CL systems is also evident: limited substances can be detected. In order to extend the applications of this analytical method, two new CL systems, cataluminescence and dielectric barrier discharege induced CL (DBD-CL) are studied in this dissertation. These two CL system, especially the novel DBD-CL system, are sensitive to more substances.In detail, this dissertation includes the following studies:(1) Based on a tungsten-coil electrothermal atomizer and a handheld CCD spectrometer, a tungsten-coil electrothermal atomic absorption spectromter (TC-ET-AAS) was constructed. Compared to the conventional ETAAS, graphite furnance (GF) -ET-AAS, the TC-ET-AAS not only greatly simplifies the instrumentation but also greatly reduces the instrumental size and cost (both for instrumental and maintainence), while process similar performance with GF-ET-AAS. Differ to the former report about TC-ET-AAS, the work in this dissertation systematically evaluated the influence of H2 concentration in Ar purge gas and then successfully applied it to analyze bio-sample. This system is promising to be a powerful complement to graphit furnance-ET-AAS.(2) Mercury free atoms were found as the initial products from the reaction between methylmercury chloride and formic acid at the presence of UV irradiation. Direct atomic absorption measurement of the newborn Hg atoms based on a handheld CCD spectrometer in the aqueous reaction media revealed that they produced a broadband absorption at around 255 nm with a half-height bandwidth of about 15 nm due to the hydration effect. This method obtains aqueous atoms at room temperature and atomospheric pressure and detects them without gas-liquid separation, which is potential to develop as a portable AAS instrument for methylmercury analysis in a simple way. Continuous UV irradiation caused the generation of Hg species related to the photo-induced decomposition of formic acid, resulting in non-wavelength selective absorption which agreed with the computation results. Thus, products of this reaction were time-dependent. Further experiments showed that the UV irradiation effectively acted as a"light switch"to control this reaction. Insight into this reaction was discussed based on these experimental and computation results.(3) A simple and miniaturized molecular fluorescence spectrometer based on a handheld CCD spectrometer was constructed for on-line monitoring of the photo-degradation of pollutants. A high pressure Hg vapor lamp was used for the UV photo-degradation and simultaneously for the fluorescence excitation. Phenol and 2-naphthol were selected as the targets for this preliminary study. Degradation efficiencies with different homogeneous photocatalyst systems were investigated, including UV only, UV/H₂O₂ and UV/Fe³⁺ degradation systems. The kinetics modeling showed that their photo-degradation fitted the Langmuir-Hinshelwood model. Results showed that the proposed method was applicable to both on-line real-time monitoring and field analysis.(4) Using porousγ-Al₂O₃ and Fe₂O₃, a cataluminescence detector for gas chromatography (GC) was proposed, and its potential application in indoor air pollution analysis was reported. By selecting proper conditions for GC separation and cataluminescence reaction, the mixture of formaldehyde, benzene, toluene, xylene and H₂S, five common indoor gaseous pollutants, can be well separated and detected by a cataluminescence detector composed with porousγ-Al2O3 and Fe2O3. Although the sensitivity of the new detector needs to be further improved, its unique features, such as applicability to both inorganic H2S and organic components, simplicity, mild working environment, and low cost, make it promising to be a competitive or complementary GC detector.(5) Based on an atmospheric pressure dielectric barrier discharge (DBD) device, a novel chemilunescence (CL) method was put forward. Analyts can be splitted in the DBD plasma, and the DBD-split/excited species can be swept into luminol solution to produce chemiluminescence (CL) emission. Based on this observation, a novel optical sensor was proposed and preliminarily tested as a gas chromatographic (GC) detector in this work. The advantages of the new type of sensor/detector include: direct detection, high sensitivity, versatility (sensitive to a broad range of organic gases), simple and easy instrumentation, compactness, and low power requirement (less than 5 W). It was found that the CL signal was proportional to the organic gas concentration, and affected by the DBD parameters. Under the optimized experimental conditions, the limits of detection down to the sub-ng level were achieved for methanol, ethanol, propanol, formaldehyde, and acetaldehyde. This is the new application of DBD in analytical chemistry, and CL is for the first time generated in this way. The new organic gas sensor can be a potential GC detector suitable for a wide range of volatile organic compounds.