Kyle J. Czech

The concentration of ethanol in hand sanitizer was determined using a calibration developed with an automated ATR sampling accessory.

Ethanol-based hand sanitizers have been used to hamper the spread of infectious diseases for decades, especially by healthcare providers. More recently, in response to the COVID-19 pandemic, hand sanitizers have become a popular household item and are now being used routinely by the general public. To effectively destroy viruses such as SARS-CoV-2, the concentration of ethanol must be greater than 60% in volume.


Fourier transform infrared (FT-IR) spectroscopy with attenuated total reflectance (ATR) requires no sample preparation and is an ideal way to determine the concentration of ethanol in a popular hand sanitizer. Here we created a calibration curve from prepared standards, using the PIKE Technologies’ AutoATR—an automated 24-well plate accessory that is designed for rapid calibration development and validation.


Ethanol standards were prepared with 99.5% anhydrous ethanol at concentrations of 0.00, 50.00, 75.00, 79.17, 85.00, and 90.00% ethanol (v/v). Each solution was covered and allowed to degas while thoroughly mixing.


FT-IR spectra were collected on a commercial FT-IR spectrometer equipped with a DLaTGS detector, and using the AutoATR sampling accessory. Then, 32 scans were co-added and the spectral resolution was 4 cm

. The PIKE AutoPRO7 software was used to control the X-Y stage of the accessory and to signal the FT-IR instrument to collect each background at each sample position prior to the introduction of the sample aliquots. After background collection was complete, sample aliquots were distributed into the 24-well ATR microtiter tray, and covered with an airtight seal to prevent evaporation of ethanol and water within each well. Each sample spectrum was collected and a transmittance spectrum was automatically calculated using its corresponding well-specific background spectrum, as directed by AutoPRO7.


The two prominent ethanol spectral bands located near 1045 and 1087 cm

, corresponding to C–O stretch modes, were analyzed (Figure 1a). The calculated area across the 975−1150 cm

spectral region of each standard solution was used to generate a calibration plot. A linear regression of the calibration series exhibiting an R2 = 0.9992 was then used to determine the %ethanol (v/v) of a popular ethanol-based hand sanitizer. Based on the linear regression equation shown in Figure 1b, the %ethanol (v/v) of the tested hand sanitizer was determined to be 82.7%.

(a) Absorbance spectra of ethanol/water standards (green lines) and the analyzed hand sanitizer (black line). (b) Calibration plot showing the area of the absorbance bands of ethanol (green markers) with the absorbance area of the hand sanitizer shown by the black marker.


Implementing automation in the laboratory offers an opportunity to increase laboratory efficiency by significantly decreasing calibration-and-validation development time. In the case of the AutoATR, up to 24 samples in a single run may be analyzed with high reproducibility and speed, resulting in high-quality spectra.



To effectively combat pathogens like SARS-CoV-2, manufacturers of hand sanitizers must determine the concentration of components in mixtures. The AutoATR makes these spectroscopic analyses easy and efficient by speeding the calibration development and model validation, while allowing for rapid sample data collection.


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Articles

Quantifying Ethanol Concentration in Hand Sanitizer via Automation

Mixtures of methanol in ethanol were investigated using an automated ATR accessory. The spectral bands of methanol and ethanol were evaluated showing the expected absorbance changes. 

	Quantitation of contaminants and toxins within human-consumable products is a critically important aspect of ensuring consumer safety. Methanol contamination of consumable alcoholic beverages is particularly concerning due to the acute toxicity of methanol, with 4 mL of ingested methanol leading to irreversible vision loss and 30 mL of methanol potentially resulting in death (1). Recently, headlines discussing deaths and injuries linked to methanol contamination of commercially available liquors at popular resorts have emphasized the importance of methanol screening and quantitation methodologies.

	Here, we use PIKE Technologies' automated ATR accessory, the AutoATR, to observe the spectral changes over various concentrations of methanol in ethanol (Figure 1). The AutoATR uses 24 unique Si ATR elements, which have a thickness of 500 microns. The thin profile of the ATR crystal minimizes absorption of the IR source by the Si phonon bands which, in combination with the accessory's base optics, results in high energy throughput and reproducibility.


	Figure 1: PIKE AutoATR automated ATR accessory.

	Sampling automation is made possible by the AutoPRO7 software package. AutoPRO7 streamlines the collection of all background and sample spectra, reducing the required user involvement to the distribution of samples after the background spectra acquisition has completed.

	A series of five concentrations of methanol in ethanol were investigated, including 0, 10, 20, 30, and 40% 

 methanol in ethanol. Each mixture was created using an Eppendorf micropipette and high-purity methanol and ethanol. After each mixture was created, a clean micropipette tip was used to distribute 120 μL of each solution into the AutoATR well plates after the background spectra acquisition was completed.

	The ATR spectrum of each methanol/ethanol sample is shown in Figure 2. The dominant spectral bands of ethanol correspond to the 1087 and 1046 cm

, while methanol exhibits a characteristic spectral band at 1033 cm

. The complementary change in concentration of the two species is highlighted by the isosbestic point at 1036 cm


	Figure 2: ATR spectra of each % v/v methanol in ethanol, collected with the AutoATR.

	Quantitation of contaminants and toxins such as methanol is critically important to ensuring the well-being of consumers. In order to streamline these measurements, automated technologies such as the AutoATR provide a uniquely accurate and high-throughput approach to ATR-based chemical identification. The AutoATR has proven capable of spectrally distinguishing methanol from ethanol and is well-suited for quantifying individual species in mixed solutions.

Clinical Chemistry, Immunology and Laboratory Quality Control

 (Elsevier, San Diego, California, 2014), pp. 317–335.


	6125 Cottonwood Drive, Madison, WI 53719
	tel. (608) 274-2721, fax (608) 274-0103
	Website: 

Kyle J. Czech

Articles

Quantifying Ethanol Concentration in Hand Sanitizer via Automation

An Observation of Methanol in Ethanol Using Automated ATR Spectroscopy