A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in vacuum systems. When constructed as a quadrupole mass analyzer, there exist two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). 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. These impurities can be measured down to Torr levels, possessing sub-ppm detectability in the absence of background interferences. RGAs would also be used as sensitive in-situ leak detectors commonly using helium, isopropyl alcohol or other tracer molecules. With vacuum systems pumped down to lower than Torr—checking of the integrity of the vacuum seals and the quality of the vacuum—air leaks, virtual leaks and other contaminants at low levels may be detected before a process is initiated. Open ion source OIS is the most widely available type of RGA. Residual Gas Analyzers measure pressure by sensing the weight of each atom as they pass through the quadrupole. Cylindrical and axially symmetrical, this kind of ionizer has been around since the early 1950s. The OIS type is usually mounted directly to the vacuum chamber, exposing the filament wire and anode wire cage to the surrounding vacuum chamber, allowing all molecules in the vacuum chamber to move easily through the ion source. With a maximum operating pressure of Torr and a minimum detectable partial pressure as low as Torr when used in tandem with an electron multiplier. OIS RGAs measure residual gas levels without affecting the gas composition of their vacuum environment, though there are performance limitations which include: Outgassing of water from the chamber, from the OIS electrodes and most varieties of 300-series stainless steel used in the surrounding vacuum chamber due to the high temperatures of the hot-cathode source (> 1300 °C). Electron Stimulated Desorption (ESD) is noted by peaks observed at 12, 16, 19 and 35 u rather than by electron-impact ionization of gaseous species, with the effects similar to outgassing effects. This is frequently counteracted by gold-plating the ionizer which in turn reduces the adsorption of many gases. Using platinum-clad molybdenum ionizers is an alternative. Closed ion source With applications requiring measurement of pressures between and Torr,