Research On The Gas Density Distribution In The Ion Source And The Chromatography Flow Control Of GC-MS

Gas chromatography-mass spectrometry (GC-MS) is a necessary tool for routine analysis of many organic compounds. The sensitivity and plasma flow stability of GC-MS in our country lags far behind the similar products abroad. Since the development and improvement of GC-MS completely depends on the performance of gas chromatography and mass spectrometer, this thesis focuses on gas density distribution of the ion source and the chromatography flow control of the GC-MS.One of the ionization efficiency factors is ion source gas density distribution. Based on the gas field theory, the gaseous distribution in the electron impact ion source (EI) of GC-MS is studied with computational fluid dynamics (CFD) method. It is shown that the gaseous distribution in the ionization region of the EI will be highest when the injection capillary is placed at a special depth, but the diameters of the capillary have almost no impact on the gaseous distribution.During the heating process of the capillary gas chromatography, the carrier gas viscosity and the damping increase, and the capillary column flow rate declines. The article discusses the relationship of the temperature, pressure and the flow rate during the temperature program, and provides a theoretical basis for constant flow by a pressure program. On the basis of the original chromatographic SP2020, we build the electronic pressure control system to achieve constant flow. And we discuss the similarities and differences of the constant pressure mode and constant flow mode. Experimental results show that the control accuracy of the electronic pressure system can achieve in less than 6% of reading in the 50°C ~ 200°C. And the GC-MS usually works in the constant flow mode. Compared to constant flow mode and constant pressure mode, Constant flow mode can ensure the accuracy of retention time. And constant flow mode can shorten the analysis time and improve efficiency of the instrument, also can improve the retention time's qualitative and chromatography's quantitative reproducibility and accuracy of the instrument.