SmartAnalysis: A sustainable digital-image colorimetry method for ethanol determination in alcohol-based hand sanitizer

Introduction: The consumption of alcohol-based hand sanitizers has increased significantly after the pandemic caused by SARS-CoV-2. Despite the conclusion of the health emergency declared by the WHO in 2023, the habit of sanitizing hands with ethanol-based gel sanitizers has been globally adopted by the population. Since general methods described in official compendia for ethanol determination such as gas chromatography or distillation are laborious and not-specific to carbomer-containing gels, this work proposes an alternative method based on digital image colorimetry. Method: The digital image (provided by ethanol-phenolphthalein reaction) was captured and transformed into an analytical signal based on the Red-Green-Blue system. The image acquisitions were performed using a Samsung Galaxy J6 smartphone, and the signals were generated using the Photometrix Pro® free program. The method was validated in accordance with ICH and applied in commercial samples. Additionally, the proposed method was evaluated for its environmental impact using the Green Analytical Process Index (GAPI) tool. Pictograms were generated using the ComplexGAPI® free program. Results: Green channel exhibited a linear response in the calibration curves for ethanol concentrations ranging from 5 to 40 % (w/w) in acidic medium. The method showed linearity, precision, accuracy, and robustness. Conclusions: The proposed method presented as main advantages the use of low-cost and easy-to-handle devices and reduced reagent consumption, in accordance with green analytical chemistry principles.