Mass spectrometry has the characteristics of high sensitivity and strong qualitative ability, but it is difficult to identify and quantify multi-component complex mixtures; chromatography has the characteristics of efficient separation of multi-component mixtures and simple quantitative analysis, but its qualitative ability is poor. The combination of the two analytical techniques can complement each other to expand the scope of application. The chromatograph is an ideal injector for mass spectrometry. After chromatographic separation, the sample enters the mass spectrometer in the form of pure substances, thereby avoiding complex mixtures from entering the ion source at the same time, which is convenient for detection; the mass spectrometer is an ideal detector for chromatography. It can detect almost all compounds and has high sensitivity.
What is the Principle of Chromatography-mass Spectrometry?
Chromatographic separation is carried out under normal pressure, while mass spectrometry requires high vacuum. If it is gas chromatography-mass spectrometry (GC-MS), the carrier gas of the chromatograph cannot enter the mass spectrometer; if it is liquid chromatography-mass spectrometry (LC-MS), the solvent of the chromatograph cannot enter the mass spectrometer. When the two are used together, there must be an interface conversion to achieve the purpose of decompression, separation of carrier gas, and concentration of the measured components. The interface is also called a molecular separator, which is an important component of the chromatography-mass spectrometry instrument. The carrier gas and sample molecules introduced from the GC are accelerated and ejected into the injection chamber through a small hole. The sample molecules with a larger mass move in a straight line under the action of inertia and enter the trap. Due to the small mass of the carrier gas and the fast diffusion rate, they are easily pumped away by the vacuum pump. The chromatographic effluent falls directly on a moving stainless steel conveyor belt. The solvent evaporates during the heating process of the infrared reflector. The sample evaporates in the heating chamber near the ions and enters the mass spectrometer system. Then, the conveyor belt uses a scavenging heater to remove the residual sample.
What are the Systems of Organic Chromatography-mass Spectrometry?
The basic structure of organic chromatography-mass spectrometry has two systems: GC-MS and LC-MS, which can be converted for use. The working procedures and result processing are automatically controlled by computers. In recent years, due to the improvement of system software and the expansion of computer capacity, more and more data processing functions have been incorporated into computer programs in the software, which has improved the speed and the work efficiency of computers.
For example, mass conversion and normalization can be performed in real time during mass spectrometry scanning, and the resulting image will be displayed on the fluorescent screen as soon as the scan is completed. During the chromatographic-mass spectrometry acquisition process, the total ion flow chromatogram of the source compound can be tracked and displayed, and any mass spectrum corresponding to the chromatographic peak can be given, such as any mass spectrum-chromatogram, three-dimensional space mass spectrum-chromatogram, extreme mass chromatogram, etc., and a certain amount of high-resolution spectrum can be given, and spectral library search can be performed.
What are the Applications of Chromatography-mass Spectrometry Analysis?
Since chromatography-mass spectrometry analysis combines the advantages of both chromatography and mass spectrometry, it has been widely used in the qualitative identification, quantitative analysis, and structural speculation of complex organic mixtures. This technology has been applied to the fields of petroleum, chemical industry, medicine, organic synthesis, fine chemicals, polymer materials, natural organic compounds, etc.
For example, petroleum fraction is a mixture of multiple components and a wide boiling range. Using high-efficiency capillary chromatography-mass spectrometry analysis, more than 240 hydrocarbon components can be quickly separated and qualitatively identified. Chromatography-mass spectrometry has been increasingly widely used in related disciplines such as life sciences, pharmacology, toxicology, environmental science, forensic medicine, and clinical medicine.
