HYPERTHERMAL SURFACE IONIZATION DETECTOR FOR GAS-CHROMATOGRAPHY

以氧化铼（ReO_2）和铂（Pt）为材料，对分子动能对表面电离的影响进行了实验研究。样品分子为苯、甲苯、邻二甲苯和哌啶。采用种子超声速分子束法将其加速到5 ~ 15 eV的动能。这些加速的分子从喷嘴中膨胀出来，通过碰撞与加热的表面相互作用，形成完整分子或其碎片的正离子。电离率是作为入射动能、表面温度和系统参数的函数来测量的。电离产率在阈值动能以上呈指数增长。这个阈值能量几乎等于能隙phi-IE，其中phi是表面的功函数，IE是有机分子的电离能。在电离效率方面，有机分子对表面温度敏感。利用这种电离原理自制气相色谱检测器，并与市售fid检测器进行了比较，评价了其功能。评估函数包括检测灵敏度、噪声水平、背景水平、动态范围、峰宽和其他系统参数。我们的探测器采用氧化铼表面，对各种有机分子的检测灵敏度比fid探测器高近100倍。噪声水平和峰宽与fid检测器相当。另一方面，其动态范围和背景电平稳定性较fid检测器差。

An experimental study was performed on the influence of the molecular kinetic energy in surface ionization, using Rhenium oxide(ReO_2) or Platinum(Pt) surfaces. Sample molecules were benzene, toluene, o-xylene, and piperidine. They were accelerated to kinetic energies of 5-15 eV by means of seeded supersonic molecular beam method. These accelerated molecules, expanded from a nozzle, were brought to interact with a heated surface by collision, forming positive ions of intact molecules or its fragments.Ionization yield was measured as a function of incident kinetic energy, surface temperature, and system parameters. The ionization yield was increased exponentially above the threshold kinetic energy. This threshold energy was nearly equal to the energy gap phi-IE, werer phi is the work function of the surface and IE is the ionization energy of the organic molecule. The organic molecules were sensitive to the surface temperature, in terms of the ionization efficiency.A home made detector for gas-chromatography with use of this ionization principle was evaluated its function, by comparison with the commercial FID-detector. The evaluated functions were the detection sensitivity, noise level, background level, dynamic range, peak width and the other system parameters. Our detector using Rhenium oxide surface showed excellent detection sensitivity, which was nearly 100 times higher than FID-detector for various kinds of the organic molecules. Noise level and peak width were comparable to those of FID-detector. On the other hand, the dynamic range and the background level stability were poorer than those of FID-detector.