質量分析計用化学電離イオン源

抄録

A Hitachi RMU-6D mass spectrometer has been modified to permit chemical ionization studies. A new source pumping system gives a pumping speed of 700 l/sec at the source and of 120 l/sec at the analyzer tube. A new ionization chamber has an electron entrance slit of 0.05mm × 3 mm and an ion exit aperture of 0.4 mm∅. A reaction gas(CH₄)was introduced into the ionization chamber of the mass spectrometer at pressure of 1.2 Torr. In this condition a pressure ratio of 6×10⁴ to 1 could be maintained between the ionization chamber and the analyzer tube by means of differential pumping. A high sensitivi ty in the chemical ionization mode has been obtained at the electron accelerating voltage of 108 eV. We have studied various secondary ions formed in methane at elevated pressures and have observed that ion currents of the major secondary ions increase linearly to the pressure, and depend on the ele ctron accelerating voltage and ion repeller voltage. The stabilities of the reactant ion current and fragment ion current are 2% and 5.6%, respectively, Several compounds(2, 2, 5-trimethyl hexane, 2-propanol, n-amyl alcohol, 4-methyl hexanol)have been used as sample gases. CI spectra of alcohols consist of an intense ion peak with m/e=[(M±1)-18]⁺which will be the quasi-molecular ion for alcohols.