Determination of the composition of mixtures of fatty acid polymorphs by DTA

The effect of various solvents on the crystal structure of pure stearic acid crystallized from them was studied using X-ray and differential thermal analysis. The latent heat of the phase transition, ΔH_t, was measured for the two well-defined forms B and C.X-Ray diffractograms are the means for the identification of crystal modifications. However, only qualitative information about the composition present in the mixture can be inferred from the relative peak intensities.Differential thermal analysis of the phase transitions at 54°C (for B) and 64°C (for A) furnishes quantitative data for each component present in the mixture.Values of 0 and 4.9 cal g^?1 for the phase transition enthalpies were measured for the pure C form and B form, respectively. Intermediate values were found for mixtures of C and B.The interplay between the crystallization conditions (type of solvent, cooling rate and flow regime) dictates the formation of various crystal structure modifications.