A simple UV-photolysis digestion method for the determination of fluoride in fluorine-containing drugs by ion-selective electrode and spectrophotometry techniques

Abstract

A simple, effective and reliable UV photolysis digestion (UVPD) method has been developed for the determination of fluoride in pharmaceuticals containing fluorine as one of the constituents. It is based on the use of high intensity UV-irradiation in the presence of a mixture of HNO₃ and methanol. For the optimization of the UVPD procedure, three bulk drug samples namely levofloxacin, nebivolol and efavirenz, were chosen as representatives of three diverse matrices: containing single fluorine, two fluorine atoms and trifluoromethyl groups respectively. Optimization of the procedure involves an initial reaction with nitric acid followed by a UVPD approach for complete mineralization of the sample i.e., conversion of bound fluorine to free fluoride ion followed by determination by fluoride ion-selective electrode (F-ISE) and spectrophotometry based methods. Parameters affecting the UVPD method, such as acid concentration, digestion time and sample weight, were optimized to obtain the quantitative recovery (>95%) of fluoride. Quantitative recovery of the fluorine in the samples could be achieved within 20–30 min of UV exposure time for a 50-mg sample. Total digestion of the drug samples was carried out by a closed microwave digestion system and the recoveries of the fluoride were found to be low (<70%) demonstrating the capabilities of the UVPD procedure. The proposed UVPD method was successfully applied to various commercially available fluorine containing drug samples.