A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in vacuum systems.

RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc.

RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment.

RGAs would also be used as sensitive in-situ leak detectors commonly using helium, isopropyl alcohol or other tracer molecules.

Residual Gas Analyzers measure pressure by sensing the weight of each atom as they pass through the quadrupole.

Torr, the problem of ambient and process gases can be significantly reduced by replacing the OIS configuration with a CIS sampling system.

Such an ionizer sits on top of the quadrupole mass filter and consists of a short, gas-tight tube with two openings for the entrance of electrons and exit of ions.

Electrically insulated alumina rings seal the tube and the biased electrodes from the rest of the quadrupole mass assembly.

Torr and offer ppm level detectability over the entire mass range for process pressures between

The upper limit is set by reduction in mean free path for ion-neutral collisions which takes place at higher pressures, and results in the scattering of ions and reduced sensitivity.

The CIS anode may be viewed as a high conductance tube connected directly to the process chamber.

Thus the CIS ionizer produces ions by electron impact directly at the process pressure whilst the rest of the mass analyzer is kept under high vacuum.