Development and Validation of a Simple HPLC-UV Method to Assay DEET Repellents and its Application to Different Commercial Forms

Background: N’,N’-diethyl-m-toluamide (DEET) is the most widely used repellent substance worldwide. It is formulated as aerosol, solution, lotion, gel and patches. However, the official compendia report monographs to analyze only DEET drug substance and solution. Objective: In this study, an isocratic HPLC method was validated to assay DEET in lotion, gel and solution, under the same analytical conditions. Methods: The method was validated according to ICH requirements and DEET detection was achieved at around 11 min, using a C-18 column, a mobile phase composed by methanol, acetonitrile and water pH 4.5 (45:10:45), flow rate at 1 mL min^-1 and detection at 270 nm. Results: A linear relationship was observed in the range of 2.5 to 100 μg mL^-1, the method was precise (relative standard deviation < 2%) and accuracy was demonstrated by DEET recovery values ranging from 99.5 to 100.2%. The specificity was studied by a forced degradation test, where degradation products were observed after alkaline degradation and ultraviolet radiation. Appropriate resolution between DEET, degradation products and excipient peaks indicated the method specificity. Robustness was evaluated by a full factorial design, and no effect on DEET assay was observed under simultaneous variation in analytical parameters. The method was applied to assay nine marketed formulations, demonstrating its good applicability. Conclusion: The validated HPLC method was successfully applied to the quantitative analysis of DEET in lotion, gel and solution, contributing to improve the quality control and the efficacy of these formulations.