MASS SPECTROSCOPE

PURPOSE: To obtain a mass spectroscope suitable for realizing the chemical ionization in the ionization part of a reaction gas without introducing the reaction gas into an ionization space by means of an electron impact. CONSTITUTION: A specimen, introduced from the direction of an arrow 10 to a three-dimensional quadruple space 18, receives impact by an electron 9 to be ionized to be detected by a detector 14. In the case of chemical ionization, the introduction of the electron 9 into the space 18 is stopped, instead an reaction gas is ionized by a reaction gas ion source 2. A resultantly produced reaction gas ion is introduced into the space 18 by a deflecting system 5 to be ion-molecule reacted with a specimen molecule here. A resultantly produced specimen ion is detected similarly by a detector 14.