Development Of Melting Point Reference Materials By Differential Scanning Calorimetry

Melting point is an important physical and chemical property of a compound,and it is also one of the important physical and chemical parameters used in thermal analysis methods.It is of great significance for the purity determination of the analyte.At present,the development of melting point reference materials mainly adopts the capillary melting point method,but the capillary melting point method cannot be accurately quantified,and there are many interference factors.This paper uses the existing capillary melting point standard material to optimize the differential scanning calorimetry to establish the best analysis method;taking benzoic acid as an example,the purity of the raw material is comprehensively investigated to ensure that the developed melting point standard material is a high-purity substance;in the differential scanning volume In the method of thermal optimization,the melting point is determined.The main research contents include:1.Full analysis of raw materials for melting point reference materials:Take benzoic acid as an example,optimize its gas chromatography analysis conditions,and on this basis,perform qualitative gas chromatography-mass spectrometry and infrared spectroscopy;based on the principle of mass balance method,Use gas chromatography,inductively coupled plasma mass spectrometry and Karl Fischer coulometric titration to accurately quantify the organic impurities,inorganic impurities,moisture impurities and solvent residual impurities;investigate sample uniformity,stability and the introduction of quantification methods The uncertainty component of,the purity of benzoic acid is determined to be 99.75%,and the expanded uncertainty is 0.28%(k=2);2.The establishment of differential scanning calorimetry:using the existing melting point standard substance,p-nitrotoluene,the factors affecting the melting point determination of differential scanning calorimetry are fully optimized,and the key problems of eliminating thermal history are overcome,and differential scanning is established.The best method of calorimetric melting point determination;3.Preparation and determination of melting point reference materials:Based on the comprehensive optimization of differential scanning calorimetry,the melting range of benzoic acid and other substances is measured to achieve accurate melting range measurement;the uniformity,stability,and introduction of samples Focusing on the problem of melting point setting and uncertainty of differential scanning calorimetry,it is determined that the melting range of benzoic acid is 122.14℃,and the extended uncertainty is 0.23℃(k=2).4.Method verification:the capillary melting point method was used to verify the melting range of the sample to be tested,and compare whether the difference between the two is too large:the results show that the capillary method measures the melting range to be 122.16℃,and the extended uncertainty is 0.22℃(k=2).There is little difference between the two setting methods,and the method can be adopted.