Characterization of Backstreaming Fluids in High-Vacuum Systems by Gas Chromatography

Backstreaming of both diffusion-pump and mechanical-pump fluids has been a constant problem with respect to their safe and efficient operation in high-vacuum systems. In most instances, the exact nature of the backstreaming oil is unknown. This study describes a gas-chromatographic procedure that was used to characterize the composition of backstreamed samples when a polyphenyl ether, Convalex-10, was used as the diffusion-pump fluid. The backstreamed fluid used for analysis was collected and removed from specially designed collection plates mounted within the diffusion pumps, which were maintained at −75 °F. The oil samples removed from the plates were further characterized by ir, uv, and gravimetric techniques.