DSC in the chemical analysis of drugs. Determination of diclofenac in pharmaceutical formulations

Differential scanning calorimetry was applied to the determination of diclofenac in three 'Voltaren' formulas. The pharmaceutical products (soluble tablets, suppositories and vials) were selected in order to show that calorimetric analysis is an easy technique to perform and can be competitive with other conventional methods. In the tablets diclofenac (DH) was determined, without any pre-treatment, from the area of the endothermic peak which occurs at about 180%C in the DSC curve obtained in N-2 atmosphere. In the analysis of the suppositories and vials, nitrilotriacetic acid (NTA) was added to transform the diclofenac sodium salt (DS) into the thermally active form (DH). In both cases, it was necessary to eliminate the interference of excipient by cyclohexane extraction (suppositories) or by a multistep program for the DSC run (vials). The accuracy of the results and the simplicity of the procedure justify the important role of DSC in the analysis of these drugs and certainly of several other commercial products.