| Gas chromatography - mass spectrometry (GC-MS) is a closely integrated product of three modern technologies, Chromatography, Mass spectrometry and Computer technology and is also an analysis instrument system available to gain two kinds of information simultaneously including retention time and molecular structure. It is widely used in environmental, food, drug detection and other security areas.The research purpose of the essay was to offer theory and technical support for the design and optimization of GC-MS. Researches of critical technologies were carried out for the three cores in GC-MS, including ion source, mass analyzer and data processing system. The major work completed in this essay summarized as following:Firstly, using electron impact ion source (EI) as the object of study, the influence of ion source parameters on its performance was analyzed which provides a theoretical basis for the ion source. (1) Influence of parameters of EI source on its performance was analyzed. Using computer-aided simulation, studying the influence of ion source parameters on the ion beam distribution emitted from the ion source in the phase space was innovatively developed. (2) The curve of the relationship between the intensity of electron beam in the EI source and the corresponding intensity of ion was obtained for the first time by the numerical calculation of Laplace and Poisson distribution of the electric field in the ion source. Meantime, it is the first time that mass discrimination caused by the increasing of electron beam intensity was analyzed.Secondly, the quadrupole mass analyzer was taken as the object of research to find how the initial phase of limited size radiofrequency quadrupole field (LSRFQF) affects the state of ion motion in the ion source. From this, incident conditions with which ions can get through the LSRFQF entirely was achieved. And then, the relation curve of initial phase and maximum radial displacement of ion was obtained with the use of the fourth-order Runge-Kutta method. Whereby, the initial phase acceptance interval (IPAI) of LSRFQF was proposed, which can be used to measure the range of the initial phase corresponding that ions can go through the LSRFQF. Also, curves of influences of the ion initial position and the work point of the quadrupole electric field on IPAI were gotten. It is the first time that computer simulation method was combined with the theoretical derivation for systematically analyzing the influence of the initial phase on the ion movement in the phase space. And accordingly, the acceptance ellipse of radio frequency quadrupole filed was obtained.Finally, three basic components of GC-MS data processing system was the object of study including data storage structure, raw data purification and mass spectral library searching. (1) Data storage structure: based on the analysis of the characteristics of GC-MS data, aimed to improve versatility of data, a data storage structure was designed. (2) An algorithm for spectrum extraction from GC-MS data based on the model peak was first mentioned which intended to extract spectrum of target compounds from the original spectrum containing pollutants from ion source, column bleeding and matrix interference from samples. The algorithm laid a foundation for improving the accuracy of qualitative analysis when using mass spectral library searching. (3) It is the first time that vector space model (VSM) used in the information search was utilized in the mass spectral library searching. Also, the sample spectrum and reference spectrum were regarded as vectors in the vector space. And the library searching was achieved by the measurement of the similarity between the two spectra using the angle of the two vectors. The ratio calculation of peak intensities of unknown compounds spectra and reference spectra was introduced to the algorithm for the first time, which can improve the retrieval performance of the algorithm. |
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