Quadrupole Mass Spectrometry

Quadrupole Mass Spectrometry


Mass Spectrometry is a useful mechanism for gas analysis in process applications, being able to detect and measure almost all gases with low detection limits and fast response. A mass spectrometer measures the mass-to-charge ratio of the molecules in a sample and by collecting and analysing the mass spectrum we can identity and quantify which molecules are present.

Quadrupole Mass Spectrometer

The Quadrupole Mass Spectrometer (QMS) which Protea supplies contains a mass filter that is made up of 4 parallel circular rods, hence the name quadrupole. It is an instrument suitable for portable or fixed installations ideally suited to semiconductor production processes, ambient air measurements, leak testing and quality testing for the food industry.

The mass spectrometer is made up of a sample preparation and inlet system, ion source, mass filter and detector. The signal from the detector is processed by on-board electronics and a PC.

The inlet is usually a narrow capillary tube through which the analyser draws a sample at 2ml/s. The inlet capillary can be of length 1m to 10m and can be heated. For measurement of gases in the presence of liquid, a sample inlet with a membrane barrier can be supplied. This prevents liquids passing through to the analyser, while allowing gas phase molecules to pass through.

The main components of the QMS are operated under vacuum. The gas passing into the vacuum chamber is ionised by the ion source and then enters the mass filter, in this case the quadrupole. The mass filter is controlled by varying the ratio of voltages on the poles that the ions are passing through. Controlling the instrument, we can either choose a particular mass ratio to detect or we can scan a range of ratio values. The detector can either be a Faraday cup or a Secondary Electron Multiplier, whose response is processed and logged by the PC.

Protea can offer QMS analysers to operate over mass ranges of 100amu, 200amu or 300amu. As with all Protea systems, the analytical solution will be tailored to suit the application needs.

QMS Graph

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