Residual gas analyzers

Residual gas analyzers (RGAs) are spectrometers that are used to identify the gases present in vacuum environments. Residual gas analyzers perform this function by producing ionizing molecules of the gas sample, separating the resulting mixture of ions according to their charge-to-mass ratios, providing an output signal, which is a measure of the relative species present, and counting the rate at which the ions hit the detector. The spectrometers within residual gas analyzers analyze the process by which a mixture of ionic species is separated according to the mass-to-charge ratio (m/z). The analysis may be qualitative and/or quantitative. There are two common styles of spectrometric analysis used, quadrupole and magnetic sector analysis, although there are specialized and custom designs available.

Quadrupole mass spectrometers consist of an ion source, ion optics to accelerate and focus the ions through an aperture into the quadrupole filter, the quadrupole filter itself with control voltage supplies, an exit aperture, an ion detector, detection electronics, and a high-vacuum system. The mass spectrometer operates only in a high vacuum whereas the gas it is being used to analyze is often at atmospheric pressure. To reduce the pressure the gas is sampled twice using a "double sniffer" configuration.