Sensing Methanol in Hand Sanitizers

Abstract

Introduction The global health emergency due to the infectious respiratory disease SARS-CoV-2 or COVID-19 has rapidly increased the need for hand sanitizers. Public awareness about safety issues in hand sanitizers has emerged since the FDA placed a warning for 221 products (by Dec. 17, 2020) [1] that contained up to 81 vol% of toxic methanol, drastically exceeding recommended [2] limits (0.063 vol%). The ingestion of methanol-contaminated sanitizers led already to more than 700 fatalities in Iran [3] and the U.S.A. [4] since Feb. 2020. Therefore, low-cost and portable methanol detectors are needed to assist distributors, local authorities and even consumers to check product safety.Gas or liquid chromatography are most established for methanol detection in complex mixtures, but these are bulky, expensive instruments that require trained personnel, usually available only in specialized laboratories and unsuitable for on-site analyses. Cheaper, more compact and less power consuming are chemical gas sensors (e.g. Pt-loaded tungsten nitride [5] or nanoporous Al2O3-coated carbon nanotubes [6]) that detect methanol from the headspace of liquids. However, most are interfered by ethanol that is usually present at high content and none has been tested on hand sanitizers.Here, we present an inexpensive and compact device that quantifies hazardous methanol accurately in hand sanitizers by headspace analysis. We applied it to pure and methanol-spiked (0.01 – 90 vol%) commercial hand sanitizers with various compositions and compared to established gas chromatography. Method The handheld detector [7] features a separation column [8] (150 mg Tenax TA packed bed) placed ahead of a chemoresistive sensors based on flame-made Pd-doped SnO2 nanoparticles [9]. A vane pump provided the flow for sampling sanitizer headspace air and recovery. A microcontroller provided the required heating power to operate the sensor at 350 °C [9], monitored its resistance and communicated data wirelessly to a smartphone by Bluetooth or Wi-Fi. Results and Conclusions Hand sanitizers are complex mixtures containing usually ethanol, 1-/2-propanol but also humectants, odorants, denaturants and colorants. Thus, the device was evaluated on the headspace of six commercially available hand sanitizers with different compositions. When spiked with 0.01 – 90 vol% methanol (total 66 samples) to simulate the entire range of typical contamination/adulteration, the sensor quantified these concentrations accurately with high R2 of 0.99 compared to “gold standard” gas chromatography (Figure 1). More specifically, methanol concentrations at the FDA limit (0.063 vol%) were determined between 0.051 – 0.073 vol%, which should be sufficient for screening hand sanitizers. Importantly, other compounds, colorants and even gel-like viscosity did not interfere highlighting the robustness of the present device.We anticipate this device to be helpful to police, customs, distributors and consumers to check product safety. It is compact (2×4×12 cm3), weighs only 94 g and offers low power consumption (ca. 1.1 W during analysis) enabling battery-driven operation. The operation and data display are user-friendly by providing wireless communication by Wi-Fi. When combined with a breath sampler, this device is even applicable for medical screening of methanol poisoning by breath analysis [10], as established for ethanol by law enforcement [11].