An effective and low-cost method for further fluorine determination by ISE in pharmaceutical drugs after pyrohydrolysis.

A method based on pyrohydrolysis reaction is proposed for the first time for commercial pharmaceutical drugs used for the treatment of depression and hypertension for subsequent fluoride determination by ion-selective electrode (ISE). Fluorine may be intentionally included in the formulation or may be present as contamination in a wide range of concentrations, requiring a suitable method for this determination. By using the proposed method with a relatively high sample mass (500 mg), 1.0 min of pyrohydrolysis reaction time in a reactor at 1000 °C, oxygen flow rate of 300 mL min-1, water flow rate of 1.0 mL min-1, and only water as absorbing solution quantitative results were obtained. The accuracy of the method was assessed by comparing the results obtained by ISE with those by ion chromatography (IC) after microwave-induced combustion (MIC). The accuracy was also assessed by analyte recovery experiments at three levels. Recoveries were in the range of 98-102 % and the agreement with results by IC after MIC were better than 98 %. The limit of quantification using ISE was 3.0 μg g-1 for fluoride. Finally, it is important to emphasize that this is the first application of a pyrohydrolysis method combined with ISE for pharmaceutical drugs and it can be considered as fast, relatively simple, using inexpensive equipment for the sample preparation and analyte determination, as well as avoids the use of toxic reagents (water and oxygen were used). Furthermore, despite the complexity of the sample matrices, the solutions obtained after the pyrohydrolysis showed very low organic carbon content avoiding matrix effects for both ISE and IC techniques.