Mass spectrometry

Description

In mass spectrometry, an instrument is used to produce ions from molecules. Two common ways of doing this are bombarding the sample either with a beam of electrons (electron ionization) or with small molecules such as methane (chemical ionization). The initial ion, called the molecular ion, often undergoes fragmentation into a pattern of smaller molecular weight ions. The ions are separated according to their mass-to-charge ratio and their relative intensities, producing a mass spectrum. In a quadrupole instrument, the ions produced in the source enter a high-vacuum area between rod electrodes maintained at opposite polarity. The application of varying radio frequencies and DC and AC voltages allows only ions with specific mass-to-charge ratios to be ejected to the detector. In ion trap mass spectrometers, the ionization and storage of ions occur in the same location. The ion trap electrodes create a three-dimensional electric field that holds the ions. Application of an appropriate radio frequency voltage is then used to eject ions with specific mass-to-charge ratios. Mass spectrometers frequently serve as detectors for gas or liquid chromatographs

Synonyms and Related Terms

MS