Quantitation Study Of Chloroform,Benzene-D₆,Benzoic Acid And Potassium Hydrogen Phthalate

Nuclear magnetic resonance（NMR）technology is widely used in the structure identification and purity determination of organic substances,and its measurement accuracy,consistency and comparability are very important.Transfer and traceability are the main ways and means to guarantee the unity of measurement unit system and the accuracy and reliability of measurement values.As a"measuring instrument",the reference materials can be used to establish a traceability chain to the international unit system by calibrating the measuring instruments and evaluating the measurement process and samples.In this paper,the raw materials of the reference materials for NMR spectrometer calibration and the internal standard for quantitative nuclear magnetic method（qNMR）traceability are studied for quantitation,which is helpful to establish and improve the international system unit traceability chain of NMR technology and provide guarantee for the development of NMR technology in China.1.Chloroform and benzene-d₆,the raw materials of the reference materials for NMR spectrometer calibration were fully analyzed.The structures of the raw materials were identified by gas chromatography-mass spectrometry（GC-MS）and NMR.The accurate quantification of volatile organic compounds by qNMR and differential scanning calorimetry（DSC）was established.The reproducibility of the results of both methods was good,and the difference between the results and the mass balance method was less than 0.1%.Chloroform was quantified by mass balance method and qNMR method.Benzene-d₆ was determined by mass balance method and differential scanning calorimetry-quantitative NMR method（DSC-qNMR）.The homogeneity and stability of the ingredients were examined and the uncertainties were evaluated.The purity results of the raw material chloroform and benzene-d₆ were determined to be 99.5%（U=0.3%;k=2）and 99.4%（U=0.3%;k=2）,respectively.It provides a traceability basis and guarantee for the development of calibration standards for NMR spectrometers.2.The mass balance method and the coulomb method for titratable impurities were used to the quantitative analysis of high-purity benzoic acid and potassium hydrogen phthalate.To the problem that the coulomb method assumes that all titrated components are all principal components,the coulometric method with titratable impurity analysis was proposed,in which all possible titratable impurities are deducted from the coulomb method results,so that the acidic purity of the analyte is converted to chemical purity.The two valuation methods passed the consistency test.The results of the homogeneity and stability examination showed that the homogeneity and stability of the two reference material candidates were good.The results and uncertainties were synthesized,and the results of high-purity benzoic acid and potassium hydrogen phthalate purity reference materials were 99.991%（U=0.024%;k=2）and 99.983%（U=0.024%;k=2）,respectively.Potassium hydrogen phthalate is the first water-soluble qNMR internal standard with an uncertainty better than0.03%.The two purity reference materials can be used for highly accurate quantitative studies of lipid-soluble and water-soluble organic compounds by qNMR,respectively,which is helpful to improve the SI unit traceability chain of qNMR in China.3.A qNMR method was developed for the analysis of benzoic acid as an internal standard.Through the selection and optimization of experimental parameters and data processing parameters,the purity determination results were reproducible with standard deviation less than 0.03%.Cross-validation of purity was performed with benzoic acid using three internal standards traceable by SI units.The purity determination results of all three internal standards were in agreement with the standard values,which proved the reliability of the cross-validation experiment.The qNMR result for benzoic acid was 99.990%（U=0.054%,k=2）,which was consistent with the fixed result of 99.991%（U=0.024%,k=2）for the reference material.The developed high-purity benzoic acid purity reference material was proved to be accurate and reliable in quantitative terms,traceable and equivalent to the qNMR purity attribution of the other three internal standards,and provided an accurate and reliable traceability basis for the qNMR research in China.