Compact colorimetric method for determining formaldehyde in indoor air: Applying to an environment contaminated with hand sanitizer vapor

Hand sanitizer, widely used during the COVID-19 pandemic, must contain at least 60 % ethyl alcohol (ethanol) as an active ingredient. Due to its high vapor pressure, ethanol is rapidly transformed into vapor after the application over any surface. However, depending on the indoor air conditions, ethanol can rapidly oxidize to formaldehyde near harmful concentration levels. This study describes a simple and sensitive method to determine parts-per-billion (ppb) of gaseous formaldehyde using a cuvette (1.5 mL polystyrene, path length: 10 mm) as a microimpinger. Indoor and outdoor air was collected by the microimpinger containing 500 μL of 3-Methyl-2-benzothiazolinone hydrazone (MBTH) (2.32 × 10−3 mol L−1) at 50 mL min−1, resulting in a blue product after 30 min of sampling. Absorbance was measured at 680 nm and is proportional to the sampling period, analyte concentration, and sampling flow rate. Under the established conditions, a limit of detection of 7.0 ppb was achieved, which can be improved using longer sampling times. The analytical method was used to evaluate the oxidation of ethanol vapor by ozone in the indoor air. 10 min after the application of hand sanitizer, the air sample taken over the next 30 min revealed a notable rise in the concentration of low molecular weight aldehydes, measured as formaldehyde equivalent, within the room's air, and can reach around 100 ppb, which may be responsible for effects such as watery eyes, burning sensations in the mucous membrane, and difficulty breathing. The present technique affords a simple, inexpensive measurement with very little reagent consumption. Besides, the method is selective and highly sensitive. This method could be used either in outdoor or indoor environments.