The principle of EI source: Its main working principle is that the filament emits electrons, which are focused and passed through the ionization chamber to the collector under the action of a magnetic field. At this time, the sample molecules entering the ionization chamber are ionized under the action of electrons with a certain energy, and the ions are focused and accelerated into an ion beam and enter the mass spectrometer.
The principle of CI source: It consists of an ionization chamber (ion box), a filament, an ion focusing lens and a pair of magnetic poles.
The difference between EI source and CI source in application:
The main difference is that the air tightness of the ionization chamber of CI source is better than that of EI source to ensure the reaction time of the ion source. There is enough pressure.
EI source is non-selective ionization and can ionize as long as the sample can be vaporized; it has high ionization efficiency and high sensitivity; EI spectrum provides rich structural information and is the "fingerprint spectrum" of the compound; it has a huge The standard spectrum library is available for searching. The spectrum is obtained under the condition of 70eV. The spectrum has good repeatability and is called a classic EI spectrum (meaning that the ratio of the isotope peaks in the spectrum can reflect the natural isotope abundance that constitutes the ion. Distribution rules.
CI source is not only an important means to obtain molecular weight information, but also can be used to selectively detect different compounds by controlling the reaction and selecting different reaction reagents based on ion affinity and electronegativity. /p>