Uncertainty Evaluation for Purity Analysis of Organochlorine Compounds by Freezing-Point Depression Method Using Differential Scanning Calorimeter

Abstract

Purity analysis using the freezing-point depression method is qualified as a measurement method traceable to the International System of Units. In particular, it is well-known that it is one of the analytical methods for which absolute quantities can also be obtained for high-purity organic compounds. However, the evaluation of commercially available raw materials for standard solutions is normally performed using chromatography, and few examples exist of the application of the freezing-point depression method. In this study, we applied the freezing-point depression method to perform a purity analysis of polychlorinated biphenyls and other organochlorine compounds, using a differential scanning calorimeter. We then evaluated the uncertainties to examine its practical applicability. The measurement results obtained in this study for the compounds used indicated purity levels of between 99.7% and 99.9%. When we assessed uncertainty, the uncertainty for the unit of purity obtained using the freezing-point depression method, after taking into account the uncertainty in conversion from the amount-of-substance fraction to the mass fraction, could be evaluated at a practically viable level of 0.2% to 0.4%. We expect that the uncertainty evaluation method proposed here can be used to perform a quantitative evaluation of the practicality of applying a differential scanning calorimeter to purity analyses of raw materials for standard solutions.