Quantitative Nuclear Magnetic Resonance Method Used In The Determination Of Volatile Organic Compound Ethylbenzene And Trace Water

The quantitative nuclear magnetic resonance(q NMR)method is a quantitative analysis method based on the principle of nuclear magnetic resonance,which has the advantages of simple preprocessing,non-destructive,and quick analysis.In recent years,q NMR has been applied more broadly in determining the purity of compounds.For q NMR internal standard method,accurate weighing of analyte and internal standard is very important in the preparation of sample solution.When the analyte is a volatile organic compound,the volatilization of the analyte in the preparation process is easy to cause the weighing error,causing it difficult to obtain accurate weight.In addition,to expand the application scope of q NMR,it has been applied to the determination of water in materials with high water content.Despite it was used to determine trace water,the pre-treatment process is too complicated to conduct rapid determination.The first part of this thesis discusses the above-mentioned problems in the quantification of volatile organic compounds by NMR.Firstly,the chemical purity of the target analyte ethylbenzene is determined by the mass balance method,997.18 ± 0.82 mg/g(k = 2),and used as the reference value for the optimization of q NMR.Then,the sample preparation and the internal standards were optimized.It turned out that the error of weighting when using maleic acid as an internal standard by routine sample preparation was too large to get an accurate result.The calculated results differed significantly from the reference value and fluctuated vastly.After optimizing the sample preparation,the deviation between the calculated results and the reference values reduced immensely,and the reproducibility was good.Finally,ethanol having similar volatility to ethylbenzene was used as an internal standard,and the optimized preparation method was used.The calculated result was 996.81 ± 3.52 mg/g(k= 2),which was closest to the reference value and had the best repeatability.The above experimental results show that for q NMR analysis of volatile organic compounds,optimizing internal standards and sample preparation can improve the accuracy of the results,and have significance guiding for using the q NMR method to measure the purity of volatile organic compounds.In the second part,the formula for the determination of trace water in samples was derived based on q NMR internal standard method,and the feasibility of this method was verified by the accurate determination of three orders of magnitude of water standards(10.02 mg/g,1.006 mg/g and 0.103mg/g).Furthermore,the selection principle of deuterated solvent and internal standard was described in detail,the moving tendency of the chemical shift of water peak with water content was explained,and the influence of environmental humidity was explored.According to the results of the consistency test,the minimum addition amounts of water standards were proposed as 5 mg,50 mg,and 60 mg,respectively,which have guiding significance for the actual liquid samples with water contents within this range.The q NMR method proposed in this thesis has little restrictions on analytes.Meanwhile,it can avoid side reactions by using different deuterated solvents and internal standards,which can be used as a supplementary method to karl fischer coulometric titration.