Mass spectrometer is a very good instrument for qualitative identification, but it can't do anything for the analysis of mixtures. Chromatography is a very good instrument for separation, but its qualitative ability is very poor. The combination of the two can give full play to their respective expertise, so that separation and identification can be carried out at the same time. Therefore, as early as the 1960s, the research on gas chromatography-mass spectrometry technology began, and early gas chromatography-mass spectrometry appeared. In the late 1970s, this combination of instruments had reached a very high level. At the same time began to study liquid chromatography-mass spectrometry technology. In the late 1980s, the appearance of atmospheric pressure ionization technology raised the level of liquid chromatography-mass spectrometry to a new stage. Recently, among organic mass spectrometers, except for laser desorption ionization-time-of-flight mass spectrometers and Fourier transform mass spectrometers, all mass spectrometers are combined with gas chromatography or liquid chromatography. In this way, the mass spectrometer is very convenient both in qualitative analysis and in quantitative analysis. At the same time, in order to increase the structural information of the unknown analysis and increase the selectivity of the analysis, the use of tandem mass spectrometry (mass spectrometry-mass spectrometry) is also a direction for the development of mass spectrometers. That said, mass spectrometers today operate in a variety of coupled ways.
Gas Chromatography-Mass Spectrometry
GC-MS (gaschr0mat0graphy-massspectr0meter) mainly consists of three parts: chromatography part, mass spectrometry part and data processing system. The chromatographic part is basically the same as the general chromatograph, including the column oven, vaporization chamber and carrier gas system, as well as the split/splitless sampling system, programmed temperature rise system, pressure and flow automatic control system, etc. Generally, there is no chromatographic Detector, but use a mass spectrometer as the Detector for chromatography. In the chromatographic part, the mixed sample is separated into individual components under suitable chromatographic conditions, and then enters the mass spectrometer for identification.
The chromatograph works under normal pressure, while the mass spectrometer requires high vacuum. Therefore, if the chromatograph uses a packed column, it needs to pass through an interface device, a molecular separator, to remove the chromatographic carrier gas and allow the sample gas to enter the mass spectrometer. If the chromatograph uses a capillary column, the capillary can be inserted directly into the ion source of the mass spectrometer, because the capillary carrier gas flow is much smaller than that of a packed column and will not break the vacuum of the mass spectrometer.
The mass spectrometer part of GC-MS can be a magnetic mass spectrometer, a quadrupole mass spectrometer, or a time-of-flight mass spectrometer and an ion trap. Quadrupole mass spectrometers are most commonly used today. The ion sources are mainly EI source and CI source.
Another component of GC-MS is the computer system. Due to the improvement of computer technology, the main operations of GC-MS are controlled by computer. These operations include calibrating the mass spectrometer using standard samples (generally FC-43), setting the working conditions of chromatography and mass spectrometry, data collection and processing, and library. search etc. In this way, after a mixture sample enters the chromatograph, it is separated into single components under appropriate chromatographic conditions and enters the mass spectrometer one by one, and is ionized by the ion source to obtain ions with sample information, and then each component is obtained through the analyzer and Detector. Mass spectra of compounds. These information are all stored by the computer, and the chromatogram of the mixture, the mass spectrum of a single component and the search results of the mass spectrum can be obtained according to the needs. Quantitative analysis can also be carried out according to the chromatogram. Therefore, GC-MS is a powerful tool for qualitative and quantitative analysis of organic matter.
As an accessory for GC-MS instrument. There can also be direct injection probes and FAB sources, etc. But the FAB source can only be used in a magnetic double-focusing mass spectrometer. The direct sampling rod is mainly used to analyze pure samples with high boiling point. Instead of GC sample injection, it is directly sent to the ion source, heated and vaporized, and then ionized by EI. In addition, the data system of GC-MS can have several sets of databases, mainly including NIST library, Willey library, pesticide library, drug library and so on.
