Analysis of diclofenac sodium and derivatives

There are two reasons explaining why several researchers have carried out the in vitro release studies of diclofenac sodium (DFNa) using pH media of above 6.5. Firstly the pH dependence of solubility, and secondly the intramolecular cyclization suffered under acidic conditions which causes the salt to become inactivated. Nevertheless, many commercially available pharmaceutical dosage forms have no protective coat to avoid the inactivation in the gastric juices. A possible explanation may be found if reconstitution of the cyclated form takes place. It is therefore necessary to study the behaviour of diclofenac sodium when it is submitted to the action of different solutions in a wide pH range. To perform this study five analytical methods have been employed: UV-vis spectrophotometry, differential scanning calorimetry (DSC), infrared analysis (IR), X-ray diffractometry (DRX) and energy dispersive X-ray analysis (EDS).