INFLUENCE OF SELECTED VARIABLES ON HEAT OF FUSION DETERMINATIONS BY OSCILLATING DSC

The influence of variables on the determination of the heat of fusion for phases with different crystallinity was investigated using oscillating differential scanning calorimetry (ODSC). The hydrophobic drug griseofulvin (GRIS) represented a crystalline substance and the polymer polyethylene glycol (PEG) 6000, a substance of semi-crystallinity. The influence of forty combinations of frequency, amplitude and underlying heating rate was analysed. The parameters determined were melting interval, melting point and the three heat of fusion values, the conventional component Delta H, the reversible c(p),-component Delta H-c, and the irreversible kinetic component Delta H-k. The selection of amplitude, frequency and heating rate did not significantly influence the conventional heat of fusion values but had a great impact on the values of the c(p) and the kinetic components. To be able to predict the reproducibility of the heat of fusion determinations, a combined value of selected variables is introduced, denoted the degree of oscillation. A tentative evaluation of the heat of fusion values showed that the ratio Delta H-c/Delta H at an appropriate degree of oscillation might be an expression of the degree of crystallinity of the phases investigated.