Study On Internal Standard Candidates Of Quantitative Nuclear Magnetic Resonance

Quantitative nuclear magnetic resonance(qNMR)is a potential benchmark method for the determination of organic compounds,and its determination results can be traced to internal standards.At present,qNMR internal standard is scarce and cannot meet the demand of rapid development of qNMR.In order to expand the selection of internal standards,three internal standards for quantitative NMR,namely,trimesic acid,hydroquinone dimethyl and dimethyl terephthalate,are proposed in this paper.The development of the series of reference materials will be beneficial to enrich the database of reference materials for qNMR in China and expand the applications of qNMR.The main research contents are as follows:The structures of trimesic acid,hydroquinone dimethyl and dimethyl terephthalate were qualitatively analyzed by infrared spectroscopy,ultraviolet spectrophotometry,liquid chromatography-mass and nuclear magnetic resonance.The values of trimesic acid,hydroquinone dimethyl and dimethyl terephthalate were studied by mass balance method: The liquid chromatographic analysis conditions of the three candidates were determined,and the water,ash and volatile components of the candidates were determined by Karl Fischer method,thermogravimetric and headspace gas chromatography.The fixed values were respectively: 99.55% of trimesic acid;99.82% of hydroquinone dimethyl;99.85% of dimethyl terephthalate.Through the optimization of internal standard,deuterium reagent,peaks for quantification and instrument parameters,the suitable qNMR of trimesic acid,hydroquinone dimethyl and dimethyl terephthalate was established,and the purity of the three candidates was determined.The hydrogen spectrum characteristics of three substances in different solvents were investigated and their feasibility as internal targets was discussed.The fixed values were respectively: 99.56% of trimesic acid;99.83% of hydroquinone dimethyl;99.86% of dimethyl terephthalate.The fixed value is composed of mass balance method and qNMR,the results of the two groups were tested by F test and t test for equal precision and consistency.The fixed results were 99.56%,99.83% and 99.86% for trimesic acid,hydroquinone dimethyl and dimethyl terephthalate.The homogeneity and stability of trimesic acid,hydroquinone dimethyl and dimethyl terephthalate were tested.The synthetic uncertainty of the reference material was 0.31%,0.23% and 0.26%.