Capillary electrophoresis combined with mass spectrometry

Olivares, Smith and Henion proposed capillary electrophoresis-mass spectrometry (CE-MS) in 1987- 1988 respectively. In CE, the ultraviolet detector has low sensitivity because of its short optical path through the sample, especially for the detection of some compounds with weak ultraviolet absorption. In recent years, due to the emergence of new technologies such as atmospheric pressure ionization (API), electrospray ionization (ESI) and rapid scanning of new mass spectrometer, which can meet the characteristics of narrow peak shape of ce, CE-MS and CE-MS-MS have developed rapidly and are becoming one of the important routine analytical methods in the laboratory.

The mass spectrometer detector has the following characteristics:

1) is a universal detector compared with ultraviolet, laser-induced fluorescence and electrochemical detectors.

2) Because of the selectivity and specificity of mass spectrometry, it makes up for the shortage of sample migration time change;

3) The sensitivity of mass spectrometry is better than that of ultraviolet spectrophotometry;

4) Mass spectrometry can give molecular weight and structure information while detecting peaks;

5) Some mass spectrometry techniques can give multi-charge ions, which is useful for analyzing macromolecules such as sugar.

It is more advantageous to combine protein with CE.

Many modes of CE, such as CZE, MEKC, CITP, CGE, ACE and CEC, can be successfully connected with mass spectrometry detectors, among which CZE-MS is still the most widely used. MEKC-MS is rarely used because the micelle formed by adding surfactant will inhibit the signal of sample ions. ESI is the most commonly used ionization mode for MS to connect CE, which can directly transfer sample molecules from liquid phase to gas phase, and can also determine samples with large molecular weight. The mass spectrometers connected with CE mainly include QQQ, TTT, FT-ICQ, TOF and so on. The first two are commonly used. There are three kinds of interfaces commonly used in CE-MS: sleeveless interface, liquid interface and coaxial sleeve fluid interface. Both the latter two interfaces introduce supplementary liquid into the outflow part of the capillary to maintain a stable electrospray flow. The buffer used in CE-MS is preferably volatile and low concentration, so that better ion current response can be obtained. In CE combined with mass spectrometry, buffer solution with high organic solvent content (such as methanol and ethyl acetate) or nonaqueous capillary electrophoresis is often used, which is beneficial to ion spraying process and can improve detection sensitivity. The components of natural botanical drugs are often similar to those of drugs and their metabolites, and CE-MS shows advantages in separation and identification. Henion et al. separated 8 kinds of synthetic isovaline alkaloids by full scanning mass spectrometry with coaxial sleeve fluid interface, and separated 8 kinds of components from the bark of the tree, and identified 6 kinds of them. Unge et al. used the same interface to separate alkaloids from biogenic amines. In addition, ion spray (ISP) and atmospheric pressure chemical ionization (APCI) are also applied in CE-MS.