Preliminary Study On Direct Analysis Of Geological Samples By Laser Ablation And Ionization Time-of-Flight Mass Spectrometer (LAI-TOF-MS)

Presently, most of methods used to analyze geological samples are related to solution sampling system. Consequently, geological sample must be dissolved before analyzed. It's well-known that the process of sample dissolution is time-consuming and labor-intensive and it brings contamination to the sample. For the sake of an effective and convenient way to analyze geological samples, we apply the home-made laser ablation and ionization time-of-flight mass spectrometer (LAI-TOF-MS) to the field of direct analysis of geological samples. Solid sample only needs to be cleaned or to be pressed in to pallet if it is powder. Parameters of LAI-TOF-MS were optimized and the tentative methods used to determine elemental concentration and relative elemental concentration of samples were also discussed. In LAI-TOF-MS, elemental concentration was calculated by RSCs (Relative Sensitivity Coefficient) and the concentration of Mn, while relative elemental concentration was related to the mass of the measured element and its intensity in the spectrum. In ICP-MS and XRF, relative elemental concentration was the ratio of concentration of measured elements to that of Mn. Analytical processes and results of LAI-TOFMS, ICP-MS and XRF were compared.This dissertation consists of five chapters. In the first chapter, the significance and conventional methods of geological sample analysis are described. Principles and research status of laser ablation are also investigated. The purpose, meaning and major content of this thesis are presented in this chapter.In Chapter Two, the structure and principle of laser ablation and ionization time-of-flight mass spectrometer and its application in direct analysis of geological samples are discussed. The development of laser ablation and ionization time-of-flight mass spectrometry is mentioned. The main body of this chapter is the application of laser ablation and ionization time-of-flight mass spectrometer to direct analysis of geological samples. The influences of laser power density, pressure of the ion source chamber, modes of the sampling system are studied. At the end, tentative methods used to determine elemental concentration and relative elemental concentration of samples are discussed.The third chapter is about the experiments on ICP-MS and XRF. It refers to the development and fundamental principles of ICP-MS and XRF, and preparation of samples. After confirming the accuracy and precision of ICP-MS and XRF, standard reference samples GBW07123, GBW07124, GBW07125 and natural samples, such as petrified wood, garnet, beryl, tourmaline, are analyzed both by ICP-MS and XRF.In Chapter Four, comparisons of LAI-TOF-MS, ICP-MS and XRF are presented. The comparisons are related to the analytical results of geological samples, the preparation of samples and the analytical processes.Conclusion and problems existed in the LAI-TOF-MS are subjected in Chapter Five, and prospects are advised at the end of this chapter.