Residual gas analysis (RGA) is a method used to determine which gases are present in a system and in what quantities. It relies on mass spectrometry, where molecules are ionized and the resulting ions are sorted by their mass-to-charge ratio (m/z) using a quadrupole mass filter. This allows the system to detect individual gas species, fragments, and isotopes based on their characteristic mass peaks.

To identify the gas composition, the detected mass spectrum must be interpreted – a process that links measured peaks to known gases or molecular fragments. This makes RGA a powerful tool for understanding vacuum quality, detecting contaminants, and monitoring process gases in real time.

Learn more in our vacuum technology book

RGA stands for Residual Gas Analysis, referring to the detection and identification of gases that remain – or are released – inside a system. These residual gases can come from leaks, outgassing materials, process by-products, or contamination. RGA is used to monitor and analyze these gases to ensure vacuum integrity, detect contaminants, or track process gas behavior in applications like freeze drying, heat treatment, or high vacuum research.

Yes. Residual gas analysis can be adapted to different pressure ranges, depending on the application. In high vacuum systems, RGA typically analyzes low concentrations of background gases in a closed, static environment. But in processes at or near atmospheric pressure – such as thermal decomposition studies or gas reaction monitoring – RGA can be used in combination with specially designed inlet systems to handle continuous gas flow and reduce pressure before the analyzer.

This means that whether you are analyzing trace gases in a sealed UHV chamber or monitoring by-products in a heated atmospheric process, RGA can be configured accordingly to provide meaningful and reliable results.

Technically, both devices are mass spectrometers, but they serve different purposes.

A leak detector is optimized to look for one or two tracer gases – typically helium or hydrogen. This makes it simpler and faster to pinpoint leaks in vacuum systems, with a mass filter tailored to detect only those specific gases.

A residual gas analyzer (RGA), on the other hand, detects a wide range of gas species and fragments across a broader mass range. It can be used for leak detection too, but doing so with a QMS is often over the top unless you are also interested in identifying other gas species.

In short: A leak detector is a focused, cost-effective tool for helium or hydrogen detection, while an RGA gives you full gas composition insights.

A quadrupole mass spectrometer detects gases based on their mass-to-charge ratio (m/z), starting from mass 1 u (unified atomic mass unit). This includes individual gas molecules, their isotopes and fragments produced during ionization. Depending on the device and configuration, different upper mass limits apply:

Partial pressure refers to the individual pressure contribution of a single gas in a mixture of gases. In a vacuum system, the total pressure is made up of the sum of all partial pressures from each gas species present.

Residual gas analysis (RGA) measures these partial pressures to determine which gases are present and in what quantity. This is crucial for identifying contaminants, monitoring process gas composition, and evaluating vacuum quality. Unlike total pressure measurements, RGA provides gas-specific insights – essential for applications where even trace amounts of certain gases can affect product quality or process stability.

Pfeiffer offers a broad portfolio of RGA solutions, from compact setups to fully integrated high-end systems - each tailored to meet the application’s needs as precisely as required, and no more. This modular approach ensures an excellent cost-to-value ratio, whether you’re monitoring trace gases in food production, optimizing pharmaceutical freeze drying, or conducting high-sensitivity UHV analysis.

A key advantage across all systems is the PV MassSpec software. It enables real-time gas analysis with intuitive operation, customizable scan profiles, and detailed data logging. Designed for seamless integration into existing QMS systems, it supports remote access, automated routines, and precise control over measurement conditions. This makes it an ideal tool for both process-driven industries and research environments requiring reliability, transparency, and flexibility in vacuum diagnostics.