Determining the Ethanol Concentrations in Ethyl Alcohol-Based Hand Sanitizers with Different Expiration Dates Using Fourier-Transform Infrared Spectroscopy (FT-IR)

Hand sanitizer has proved to be an essential public health tool in slowing the spread of the coronavirus (COVID-19). However, amid the COVID-19 pandemic, the availability of recently manufactured hand sanitizer can be limited. The product expiration date set by manufacturers is also minimally regulated. The efficacy of hand sanitizer is entirely determined by its most volatile ingredient, alcohol, which must remain at a concentration greater than 60% (v/v) to kill bacterial and viral pathogens. In our undergraduate Chem 2123W course (Introductory Quantitative Analysis Laboratory) in spring 2021, we designed and conducted an experiment to investigate the alcohol concentration of ethyl alcohol-based commercial hand sanitizers with varying expiration dates. The presence of a primary alcohol functional group in ethyl alcohol can be observed by Fourier-transform infrared spectroscopy (FT- IR). Through a series of standard additions of ethyl alcohol to the diluted hand sanitizer sample, we measured the changes in the integration of the FT-IR primary alcohol C-O stretch. The signal changes in integration were used to generate a standard addition curve using ethanol concentration and calculate the initial ethanol concentration of each sample. Our approach accounts for this matrix effect and does not rely on a compositional approximation. All the samples studied were found to exceed the minimum concentration required to effectively exhibit antimicrobial properties despite three of the four samples being expired. However, the expired samples remained close to the 60% threshold and with consideration of error analysis, the effectiveness of these hand sanitizers remains uncertain. The samples analyzed in this study varied in reported initial ethyl alcohol concentration, manufacturer, color, perfume, and other ingredients. The heterogeneity of our samples coupled with our consistent results provided insight into consumer use of expired ethyl alcohol-based hand sanitizers.