Sanitary-Gel Drying Kinetics: A Tool for the Assessment of Quality, Exposure to Ethanol Vapor, and Fire Risk during Storage and Transport

Abstract

The quality of ethanol-based (EtOH) hand-sanitizing gels is of the utmost importance. The EtOH content needed for antiseptic action is defined by national or regional standards. A simple, noncostly methodology for the determination of EtOH content in gels is reported, based on the drying rate of gels at 50 °C and 87 kPa, determined by using affordable drying balances. This would be an asset for small manufacturing companies. A linear regression equation was obtained for the initial rate of evaporation of four EtOH–H₂O binary mixtures as a function of initial EtOH content (r_p = 0.9986), which was used as a benchmark for the determination of alcohol in gels. Agreement was found between the results obtained by this kinetic method in 19 commercial products provided by the Ministry of Economy, Industry, and Commerce of Costa Rica, and their results were obtained by gel distillation to dryness and further densimetric determination of the EtOH content in the distillate. The two sets of data agreed within a (5 ± 5) % mean absolute deviation. This kinetic method brings laboratory practicality and a cost-effective alternative for assuring the quality of this kind of product without the need for time-consuming sample preparation. It is understandable that laboratories that deem this kinetic methodology suitable for their needs must set their working conditions due to the variety of drying balances in the market. Gels evaporation rates are not only a matter of quality assessment but also useful as an index of fire risk during storage and exposure to EtOH in storage places.