GC-MS stands for Gas Chromatography-Mass Spectrometry. It combines a gas chromatograph (which vaporizes a sample into the gas phase and separates it into its various components) with a mass spectrometer, which breaks the components down into ionized fragments. This allows them to be analyzed separately for better identification and quantification.
In addition to non-specific tests for various components, GC-MS is very useful as a specific test for identifying substances. In short, it provides a 100% specific test to positively identify the presence of a specific substance.
Gas chromatography-mass spectrometry is suitable for the separation and analysis of substances with large molecular weights, complex structures, and hardly volatile and insoluble substances.
In pharmaceutical GC-MS analysis, the flash evaporation technique can be used to analyze the volatile components in Chinese herbal medicines. The so-called flash evaporation refers to the rapid heating of the sample at a lower temperature (lower than the sample’s cracking temperature) before the sample is cracked, and the volatile components are evaporated to obtain a chromatogram. The sample is then cracked at high temperature to obtain a cracked chromatogram. In this way, important information on volatile components in the sample can be obtained, which is very useful in the qualitative identification of the sample.
The identification of polymers by pyrolysis-gas chromatography is carried out by comparing the pyrograms of unknown samples and standard samples, a so-called “fingerprint” identification. Fingerprints of standard samples can be stored in a computer database or obtained by parallel experiments with unknown samples during identification. Regardless of the method, the spectra being compared are required to be obtained under the same experimental conditions.
Although the fingerprint identification method is intuitive and convenient, it is not strict, and sometimes it is often difficult to accurately judge some polymers with similar structures.
Multidimensional pyrolysis gas chromatography is also an effective method to identify polymers. Using methylsilicone and PEG-20M dual capillary column system, the cleavage products with the set retention time window on the methylsilicone column are switched to the PEG-20M column for analysis, and the characteristics of olefin polymers and nylons can be obtained. Spectrum.
There is also an internal standard identification method, that is, using polystyrene as a reference polymer to crack with an unknown sample, and then calculate the retention time of the sample product relative to styrene, and then compare it with the corresponding result of the standard sample.
In conclusion, the identification of polymers by pyrolysis-gas chromatography is a very effective method. The fingerprint identification method is intuitive and convenient. Characteristic peak identification method is a better method, but structural identification of characteristic peaks is required. The engineers of Jinjian Laboratory believe that using the internal standard method and identifying the characteristic peaks may not need to identify the structure of the characteristic product, but can ensure a certain reliability. The better way is to use the spectral library for comparison, which is convenient and fast.