Main use of thermal analysis is purity assessment of high purity organic reference materials by freezing point depression method wtih adiabatic calorimeters and DSC. And thermogravimetry is applied to impurity analysis and analysis of volatile and hygroscopic properties.
Purity assessment by freezing point depression method
Freezing point depression method is one of the purity assessment methods from the freezing point dpression owing to the impurities included in a sample. Purity was assayed from the relation between fraction melted and sample temperature during fusion and the fraction melted and the sample temperature was measured during gradual melting of the sample.bFreezing point depression method can determine the purity only from physical quantities of temperature and heat and the method is known as one of the primary methods of measurement. In our group, adiabatic calorimeters and DSC are used for purity assessment by freezing point depression method.
Impurity analysis by thermogravimetry
Freezing point depression method can detect impurities in the liquid phase during fuion, impurities evaporated from the sample and insoluble impurities to the liquid phase of the sample. As the undetectable impurities, ignition residue and loss on heating are determined by thermogravimetry.
As our thermogravimetric analyzer uses infrared heating, cooling to near room temperature is possible and it is utilized for accuracy improvement to reduce the effect of buoyance by weighing the sample at the same temperature after each heating.
Analysis of volatile and hygroscopic properties by thermogravimetry
Some of our samples are volatile and hygroscopic, and these properties cause some problems in weighing of samples for assessment of purities and impurities. Mass change due to volatility and hygroscopic effect cause biases to the assessment results. So we determine conditions of sample treatment for constant water content and for reduction of mass loss due to volatilization from the measurement of volatility and hygroscopic property with a thermogravimetric analyzer possible to control relative humidity.