“Sniffing” Toxic Methanol in Laced Beverages By a Fully-Integrated and Portable Analyzer

Abstract

Introduction In July 2019, more than 20 people died in Costa Rica due to methanol-tainted alcohol of registered and unregistered brands [1]. Similar outbreaks have been reported in India [2] (95 deaths, February 2019), Iran [3] (768 cases, 2018) or Cambodia [4] (237 cases, 2018). In fact, 5400 intoxications and 1500 deaths were reported due to methanol-tainted alcohol within the last two years [5]. Apparently, cheap methanol is intentionally added to alcoholic beverages to increase their potency and profit. In the human body, methanol is converted to formaldehyde and formic acid, which can interfere with the human metabolism leading to blindness or even death [6]. Therefore, handheld analyzers or sensors to screen beverages are urgently needed to prevent such intoxication. These could be applied by tourist or even first responders.However, compact gas sensors either suffer from insufficient detection limit (legal limit of 0.09 vol% in fruit distilled spirits [7]), cannot distinguish methanol from the chemically similar ethanol present at much higher concentration or have not been validated with real beverages. Here, we present a stand-alone, inexpensive and miniaturized analyzer for screening of potential safety hazards in beverages [8] that can be applied even for hand sanitizers. Method The handheld device consists of a printed circuit board with integrated microcontroller and circuitry to operate metal-oxide gas sensors (Figure 1a). A miniaturized pump (12 g) is used to guide the sample through a sorption filter for analyte pre-separation to a highly sensitive and flame-made Pd-doped SnO2 sensor [9]. The sample was obtained from the headspace above liquors. The device was calibrated with laboratory mixtures containing methanol and ethanol in ultra-pure water at concentrations ranging from 0.01 – 10 vol% and 5 – 80 vol%, respectively. Subsequently, the device was tested with real beverages including beer, sake, Baileys, Arrack, pear spirit and Stroh rum. The drinks were chosen to cover a wide range of ethanol concentrations (5 – 80 vol%) and flavors that might interfere with the detector. The methanol concentration of the pure drinks was determined by liquid chromatography. To generate higher methanol concentrations, the pure beverages were spiked with methanol up to 10 vol%. Results and Conclusions In laboratory mixtures, methanol (1 vol%) and ethanol (5 vol%) passed through the separation column with retention times of 1.6 and 5.3 min, respectively, that can be detected subsequently (thus selectively) by the Pd-doped SnO2 sensor. Thereby, the effective separation of methanol and ethanol is crucial. This was evaluated by comparing the retention time of methanol to the breakthrough time of ethanol. For methanol, the retention time ranged from 1.25 – 1.5 min depending on concentration, from 0.01 to 10 vol%. Importantly, the breakthrough time of ethanol was always larger than 2.2 min. This enabled reliable and simultaneous detection of methanol and ethanol, even at their lowest and highest concentrations, respectively.For all alcoholic beverages, no interference originating from the different flavors was observed on the methanol and ethanol quantification. Most importantly, the device predicted methanol and ethanol with average error of 21.9 and 13.4% (with respect to the actual concentration), when tested in 43 pure and methanol spiked beverages (Figure 1b). Also, the performance was reproducible and stable for at least 107 days. As a result, the validated device could readily be applied by laymen (e.g. tourists) or first responders to screen beverages for toxic methanol and prevent severe health damage.