. The methods used to identify the structural formula include chemical method (using chemical reaction, etc.), spectroscopic method, etc. Spectroscopic methods are very accurate and advanced methods, including ultraviolet (UV), infrared (IR), nuclear magnetic resonance (H-NMR, C-NMR), mass spectrometry (MS), etc.
If the tested component is a known compound, after determining the purity, there is no need to do a lot of identification work, just select several of them. If the standard or reference substance of known substances can be obtained, chromatographic analysis (TLC or HPLC) will be carried out for the tested component and the standard substance. If the RF value or retention time is consistent, the mixing point does not drop, the infrared spectrum is completely consistent, and the molecular weight is consistent, it can be said that the tested component and the reference substance are consistent. If no standard is available, it should be compared with the infrared spectrum (preferably the spectrum of known substances) and mass spectrum data of known substances in the literature, and sometimes with the NMR spectrum data of known substances. If they are consistent, it means that the tested components are consistent with those reported in the literature.
If the measured component is unknown, a lot of work needs to be done. For the structure determination of unknown components, we should also pay attention to the literature work, the source of the traditional Chinese medicine, the research of chemical components in the same genus, and collect information, which is very beneficial to the structure identification. There are basically two cases for the identification of unknown substances: one is a compound with a new structure, and the other is that the basic skeleton is known, but the substituents are differentOr the location is different. In the latter case, collecting literature is very useful for the medical education network to sort out the identification structure.
Identification procedure of chemical components of traditional Chinese Medicine
A compound is generally identified according to the following steps:
Determination of purity
(1) First, observe whether the shape and color are single and pure, and whether the crystal shape is consistent.
(2) Chromatographic analysis: the result of thin-layer chromatography is a single spot, so it should be noted that the spot quantity should not be too small, and the developer should not be selected only. Sometimes gas chromatography and HPLC can be used, and the result is a single chromatographic peak.
(3) Melting point measurement: the melting point distance should generally be less than 2 ℃.
Determination of physical constants
Physical constants solid samples include melting point, specific rotation, etc; Liquid samples include boiling point, refractive index, specific rotation, etc.
Molecular formula determination
The molecular ion peak is obtained by high-resolution mass spectrometry, and the molecular formula can be obtained directly. If there is no high-resolution mass spectrometry, the molecular weight can be measured first (generally using mass spectrometry), then the elements and percentage content can be measured by elemental analysis, and the experimental formula can be calculated. The experimental value should be very close to the theoretical value.
Presumption of functional groups and molecular skeletons of compounds
The methods used include calculation of unsaturation, chemical reaction, IR spectrum, UV spectrum, NMR spectrum, MS data, comprehensive analysis, and sometimes comparison with known substances to determine the basic skeleton and functional groups (substituents) of the tested samples.
Determination of chemical structure
Through the comprehensive analysis of all spectral data, some special tests should be made when necessary, such as some new methods in NMR, and even X-ray diffraction and other tests to determine the chemical structure formula. If possible, carry out artificial synthesis, and comprehensively compare the samples extracted and separated from traditional Chinese medicine with the synthetic products to prove the correctness of the structural formula.