determination of the crystallization behavior of lipids by temperature modulated optical refractometry

This study was conducted to examine if the new temperature modulated optical refractometry (tmor) method is applicable to study the phase behavior of alkyl-based components. n-hexadecane, palmitic acid, and glycerol tripalmitate were used as model components. tmor was benchmarked against differential scanning calorimetry (dsc) and polarized light microscopy (plm). for all substances, a good agreement of the dsc data with tmor was found. for n-hexadecane, a difference of 2.2 °c for the crystallization and 2.6 °c for the melting temperature was found. considering palmitic acid, the crystallization temperature differed by 3.3 °c while the melting varied by 2.8 °c. the crystallization temperature of tripalmitate identified by tmor was 2.7 °c higher, and the melting temperature 2.3 °c was lower compared to the dsc. the crystallization temperature for tmor was always higher, and the melting temperature was always lower if related to dsc. this leads to the conclusion that tmor is more accurate and direct. in addition, the transition peaks identified by tmor were narrower compared to the dsc peaks. this is due to slower heating and cooling rates leading to a smaller temperature range of phase transition and less thermal lag. the study showed that tmor is an appropriate method to determine the phase transition temperatures for the three examined substances. the results were comparable to the dsc data in both melting and crystallization behavior. since the accuracy of tmor is better at lower heating and cooling rates, it could be a reasonable extension of the well-known dsc method in the studies of melting and crystallization.