Analytical apparatus with variable energy ion beam source

Abstract

Disclosed herein is an analytical apparatus comprising a gas chromatograph, a mass spectrometer, and an interface connecting the two. The mass spectrometer comprises a variable energy ion beam source, a magnetic sector of substantially fixed magnetic field for deflecting the ions in the ion beam according to their momentum, and a detector for detecting those ions within the ion beams which have been deflected by a given angle by the magnetic sector. The variable energy ion source comprises a repeller electrode, a first low energy alignment electrode coacting with the repeller electrode to define an ion-forming region, an inlet means for introducing gas into the ion-forming region, means for forming an electron beam in the ion-forming region, a second high energy alignment electrode, and an entrance electrode separating the ion beam source from the magnetic sector. The repeller electrode is maintained at a constant potential relative to the first alignment electrode, the second alignment electrode is maintained at a potential more negative than but proportional to that of the first alignment electrode, and the first alignment electrode is maintained at a potential positive with respect to entrance electrode. By varying the potential of the first alignment electrode relative to the entrance electrode, the mass spectrum can be swept.