Research And Application Of Nuclear Magnetic Resonance Method For The Targeted Detection Of Complex Systems

Nuclear magnetic resonance(NMR)technology is a modern instrumental analysis technology,which is known as the high sensitivity and detection accuracy.NMR has been widely used in chemistry,food,materials,medicine,energy survey and many other fields.However,due to the problem of signal overlap,it is often difficult for the conventional NMR techniques to accurately analyze the components of a complex mixture system.In view of this deficiency,two new NMR methods for composition analysis and characterization of complex mixtures were developed in this thesis.The developed methods were applied in some practical systems.The main research work of this these is as follows:1.Aiming at the shortage of the traditional NMR technology to accurately analyze the composition of a complex mixture,an NMR spectral editing method based on nuclear spin singlet state was developed.By using the developed method,the targeted observation of the~1H NMR signal of glutamate was successfully achieved.Due to the complex nuclear spin coupling system of glutamate,the conventional pulse sequences for nuclear spin singlet state preparation,such as M2S,g M2S,and SLIC,cannot be used to effectively prepare the singlet state of glutamate.According to the characteristics of the nuclear spin system of glutamate,a new pulse sequence based on the optimal control was designed in this work.By using the pulse sequence,the preparation of glutamate nuclear spin singlet can be successfully achieved.On this basis,the signal of glutamate can be selectively observed.Using the developed pulse sequence,the targeted detection of glutamate molecular signals in complex mixed solutions was achieved.2.Aiming at the shortage of the traditional NMR technology to identify the substances with similar compositions,the NMR relaxation fingerprint technique based on two-dimensional nuclear magnetic resonance relaxation measurement was developed,which was used to successfully achieve the quality identification and adulteration of common edible vegetable oils.Due to the similar chemical structure and composition of different edible vegetable oils,both traditional NMR spectroscopy and relaxometry cannot effectively identify edible vegetable oil types and detect adulterations.According to the characteristics of edible vegetable oil,a new NMR relaxation fingerprint sequence based on two-dimensional NMR relaxation measurement was designed in this work.By using the developed method,we successfully achieve the rapid identification of edible vegetable oils and oil adulteration detection.The measuring time per sample is less than 10 minutes.This is much shorter than the measuring time of the traditional techniques for the identification and adulteration of edible vegetable oils,which usually take 5-7 working days for one sample.This method has been tested in Zhangjiagang Customs and was well approved by the relevant departments in Zhangjiagang Customs.