High sensitivity mass spectrometer system for contaminant measurement in high purity gases

A mass spectrometer beam system using a double focusing sector analyzer and an electron impact ion source has been developed for trace analysis. The molecular beam, formed through a focusing glass capillary array, serves as the gas inlet of the system. Closed cycle cryopumps and ion pumps are used to generate the high vacuum. System roughing is achieved using sorption pumps. Clean and oil free vacuum was obtained by nonmechanical pumping. System normal mode sensitivity is about 107 counts/s/Torr. System low pressure mode sensitivity can be three orders of magnitude higher when sample pressures are below 30 mTorr. A parts‐per‐billion range system detection capability was accomplished. Slow response time for adsorptive species measurements is a major drawback of the sample inlet system.