| Terahertz waves are high-frequency electromagnetic waves.Among the many characteristics of the terahertz wave,the "low energy" and "fingerprint characteristics" enable the terahertz wave to be applied to the nondestructive detection of many substances.In the course of thousands of years of historical development in China,Chinese herbal medicine has shown extremely important medical value in the treatment of plague,and it is also true in today's society.Therefore,strictly controlling the quality of Chinese herbal medicines is conducive to ensuring the safety of patients' lives and can promote the long-term development of Chinese herbal medicines.Traditional identification method and modern identification method are the main methods currently used in the detection of Chinese herbal medicine in China.Although traditional identification methods are widely used in research because of their advantages such as simplicity and low cost,the accuracy of identification depends to a certain extent on whether the operator has rich knowledge and experience in medicinal materials.With the development of spectral analysis technology,modern identification methods based on spectral analysis technology have gradually entered people's field of vision.Theories and a large number of experimental studies have shown that the intramolecular vibration mode of the Chinese herbal medicine metabolites and the low-frequency vibration of the crystal lattice occur in the terahertz band,so that the ingredients contained in the Chinese herbal medicine can be identified.This article describes the research status of terahertz time-domain spectroscopy in the detection of various substances,which lays the foundation for subsequent research.The subject first prepared elementary samples of glycyrrhizic acid,glycyrrhetinic acid,and glycyrrhizin with mass fractions.The terahertz absorption spectra of the above three elements were measured using the transmission THz-TDS platform of the Beijing Industrial Spectrum Imaging Engineering Technology Research Center.The terahertz absorption spectrum waveforms of the three are similar.Secondly,the subject carried out a qualitative analysis of glycyrrhizic acid by means of quantum chemistry,that is,constructing a single-molecule configuration of glycyrrhizic acid,using semi-empirical algorithm and density functional theory to complete geometric optimization,and calculating the frequency to obtain the terahertz of glycyrrhizic acid single molecule.Absorption calculation spectrum.Comparing the two calculation results,it is found that the semi-empirical algorithm and density functional theory are basically consistent with the experimental results in peak position and waveform,but due to the limitations of single molecules,there is a certain error between the calculated spectrum and the experimental spectrum.In order to gain a deep understanding of the interaction between the groups within the glycyrrhizic acid molecule and the formation mechanism of the spectrum,the characteristic absorption of the glycyrrhizic acid molecule matches the vibration mode.In order to study the relationship between the content of glycyrrhizic acid sample and the absorption coefficient,first,the terahertz absorption spectra of glycyrrhizic acid with mass fractions measured by the transmission THz-TDS system were used,and then a single linear regression model was used for analysis.The analysis results show that the terahertz absorption spectrum of glycyrrhizic acid complies with Lambert's law.On this basis,samples of two mixtures of glycyrrhizic acid and glycyrrhetinic acid,glycyrrhizic acid and glycyrrhizin were prepared,and the absorption spectrum of the above mixture was obtained using a terahertz time-domain spectroscopy system,combined with Lambert's law and least squares algorithm for quantitative analysis.The quantitative analysis method is an indirect detection technology,so the model evaluation parameter correlation coefficient and root mean square error are used to judge the pros and cons of the method. |
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