2.3. Thermal analysis by Differential Scanning Calorimetry (DSC)

DSC measurements were performed by a Perkin-Elmer DSC400, equipped with Pyris software for thermogram processing. Samples of 8–10 mg were placed in a flat bottomed aluminum pan and heated at a constant rate of 10 °C/min, using dry nitrogen atmosphere as carrier gas, in a temperature range of 30–400 °C. The instrument temperature and energy scales were calibrated using purified Indium (99.9%) as the standard reference material.

The thermal analysis is a valuable method to investigate drug–polymer interactions and to optimize formulations of pharmaceutical dosage forms [3]. DSC of plain drug, PGT copolymer and CIP-loaded copolymer (PGT/CIP 5:3 w/w ratio), shown in Fig. 3, were performed to determine any change in the drug melting temperature, in order to investigate possible interactions between the drug and the copolymer.

DSC analysis: thermograms of ciprofloxacin (CIP), copolymer (PGT) and their mixtures in the range 40–400 °C under nitrogen atmosphere.

The DSC data demonstrated endothermic peaks for CIP and PGT at 154 °C and 108 °C, respectively. The PGT–CIP mixture thermogram showed the disappearance of endothermic peaks of CIP and PGT and the appearance of another endothermic peak at 127 °C. CIP melting point was found at 325 °C followed by decomposition; this peak was anticipated to 310 °C when CIP was included in PGT gel.