MS - Quadrupole Mass spectrometer

The quadrupole mass spectrometer is a “partial pressure” instrument for high vacuum or ultra-high vacuum. Electrons, which have been accelerated to approximately 100 eV (typically 70 eV, for EI+ mass spectra), collide with the atoms/molecules of the sample gas (also referred to as residual gas in the literature), ionizing them in the process. The generated ions are accelerated by a static electric field and pass centrally through four parallel rod electrodes whose intersections with a plane perpendicular to the cylinder axis form a square (quadrupole). In the alternating field between the quadrupole rods, m/e selection takes place so that in each case only particles with a defined mass can pass through the field. The ions impinge on a detector with a measuring amplifier, which measures the ion current and is converted to the count rate or partial pressure by the software of the connected PC. The ionization units, quadrupoles and detectors are available in a wide variety of versions for different applications. It is available in expensive, high-resolution but also low-cost variants (as a residual gas analyzer) and thus has a high prevalence in the R&D sector.