Isotope abundance, element composition determination, etc. In order to meet these requirements, the ion sources used mainly include inductively coupled plasma (ICP), microwave plasma torch (MPT) and other microwave-induced plasma (MIP), arc, spark and glow discharge. And almost all excitation sources available for atomic emission spectroscopy are available. The detection objects of mass spectrometry are mainly organic and bioactive substances, which need some special ionization sources (relative to AES excitation sources). These ionization sources can be divided into four categories, namely electron bombardment ionization (EI), chemical ionization (CI), desorption ionization (DI) and spray ionization (SI), as shown in the following table. Except EI, each ionization source can obtain a large number of positive ions and negative ions at the same time, and the types of molecular ions are related to the medium or matrix in the ionization process. For example, CI can generate (M H), (NH4), (Ag) and (Cl) plasmas as molecular ions, and can also generate similar fragment ions.
Ionization reagents commonly used in mass spectrometry ionization sources Surface ionization sources for organic matter analysis are suitable for sample electron ionization (EI) electron gaseous sample chemical ionization (CI) gas ion gaseous sample desorption ionization (DI) photon, high-energy particle solid sample spray ionization (SI) Different ions generated by high-energy electric field hot solution ionization sources can react with each other, making the ionization results more abundant and complicated. For example, a large number of ions can be produced under the action of EI, and ions with large internal energy can spontaneously crack when colliding with neutral molecules (such as he) to produce more fragment ions. This kind of ion-molecule reaction is generally difficult to complete, and often a lot of ion fragments are obtained, leaving some parent ions. However, this can be promoted by increasing the internal energy of ions (such as adjusting collision time, EI energy and the number of neutral particles). )
The ion-molecule reaction is completed; On the contrary, if the internal energy of ions decreases, it is possible to obtain stable ions instead of fragments of ions. Compared with EI, CI, DI and SI are all soft ionization sources. With the help of laser and matrix, DI can even ionize solid compounds which are difficult to volatilize and thermally unstable, and get relatively complete molecular ions. The appearance of SI solves the problem of sampling biological macromolecules, and provides a very convenient and effective means for the application of mass spectrometry in the field of life sciences, especially for the determination of macromolecular bioactive substances such as protein and DNA. Its role has also attracted worldwide attention, because its founder won the Nobel Prize in Chemistry in 2002. To investigate the performance of ionization source, the commonly used parameters are signal intensity, background signal intensity, ionization efficiency and internal energy control ability.