Using ATR-FTIR to Ensure Product Safety of Alcohol-Based Hand Sanitizers

The Centers for Disease Control and Prevention (CDC) initially amended its hand hygiene guidelines in 2002, advising that the public and health care personnel use alcohol-based hand sanitizer rather than soap and water for hand cleansing.¹

Most alcohol-based hand sanitizers contain one or two types of alcohol - either ethanol, isopropanol or n-propanol. Alcohols’ antimicrobial activity is linked to their ability to denature proteins. The best antimicrobial efficacy can be achieved with solutions of isopropanol (60 to 80%) and ethanol (60 to 85%).²

Higher concentrations are less effective. This is because proteins require the presence of water to be easily denatured. Solutions with less than 60% alcohol may slow the growth of germs but may not kill them.

Responding to the Coronavirus Disease 2019 (COVID-19) pandemic, the Food and Drug Administration (FDA) issued guidelines^3,4 which temporarily permit compounders and other entities to prepare and distribute hand sanitizer products while the public health emergency is in effect, despite these not presently being regulated as drug manufacturers by the FDA.

Though the formulations and preparation protocols are fairly rudimentary, it is vitally important that sufficient quality assurance and control measures are maintained, in order to ensure the efficacy and safety of hand sanitizer products.

With that in mind, the use of a Thermo Scientific™ Nicolet™ iS50 FTIR Spectrometer fitted with a built-in attenuated total reflectance (ATR) accessory and working in conjunction with the intuitive, powerful Thermo Scientific™ OMNIC™ Software platform, provides a simple solution which is capable of meeting these analytical requirements.

The first step in quality control and assurance process is ensuring that a material meets the required specifications.

Figure 1 displays the FTIR spectra of three alcohols which are commonly found in hand sanitizer products: ethanol (ethyl alcohol), 1-propanol (n-propanol), and 2-propanol (isopropanol).

Figure 1. ATR FTIR spectra of three alcohols commonly used in alcohol-based hand sanitizers: ethanol, 2-propanol, and 1-propanol. Each spectrum is 16 scans co-added at a spectral resolution of 4 cm^-1.

Visible differences exist in both the C-H stretch (3000-2800 cm^-1) and fingerprint (1500-500 cm^-1) regions because of their distinct chemical structures. It should be noted that while n-propanol has been utilized in alcohol-based hand rubs in some European countries for several years, it is not currently approved as an active agent for hand sanitizer products in the United States.

QCheck™ spectral correlation provides an ideal means of verifying incoming materials, in-process materials, or finished products. In this example, the spectrum of the denatured, industrial-grade ethanol was examined and compared to the spectrum of the non-denatured, reagent grade ethanol (Figure 2).

Figure 2. QCheck result of industrial-grade ethanol against a reagent grade ethanol.

The industrial grade-denatured ethanol contains isopropanol, demonstrated by the minor peak at 950 cm^-1. The “Fail” result implies that the impurity level was found to be higher than the predefined threshold. This quality check was achieved without the need for complicated spectral manipulations or constructing libraries.

Glycerol is also a key ingredient in hand sanitizer products. The World Health Organization (WHO) recommends that only Food Chemical Codex (“food grade”) or United States Pharmacopeia (USP) glycerol be used within the formulations.⁵

Figure 3 displays the results of the incoming inspection of two different types of glycerol using OMNIC’s QC Compare function. QC Compare Search is a spectral classification technique that is able to determine the best match from each class, highlighting how closely the unknown material matches the spectrum of the selected standard.

Figure 3. QC Compare the results of two types of glycerol.

In this instance, with a critical match value of 90, one glycerol passed the inspection while the other failed.

As well as being useful in incoming material inspection, FTIR is suitable for the quantitative determination of the percentage of alcohol in hand sanitizers.

FTIR measurements were undertaken on a series of ethanol/water standards with ethanol levels varying from 25-99% (v/v). The area of the peak (878 cm^-1) was then used to build a calibration curve using Simple Beer’s Law. Thermo Scientific™ TQ Analyst™ Software (Figure 4) was used to facilitate this.

Figure 4. Calibration result of ethanol% measurements.

The calibration curve shows exceptional linearity with a coefficient of 0.9981. Next, the calibration was applied to four samples of commercially available hand sanitizers in order to predict the ethanol percentage of those products. The results are outlined in Table 1.

Table 1. Predicted ethanol percentage vs. label claim of four commercial hand sanitizer products.

The expected ethanol percentage displays excellent agreement with the label claim, with deviation from anticipated values between 0.016% to 0.28%.

As can be seen, ATR FTIR measurements are simple and easy to use, with no need for sample preparation.

The use of QCheck and QC Compare allows material quality to be easily verified, improving confidence in the quality of materials at each stage of the production cycle. Additionally, the quantitative analysis offered by TQ Analyst allows for accurate predictions of final formulations’ alcohol content.

The Thermo Scientific Nicolet iS50 FTIR Spectrometer equipped with a built-in diamond ATR, used alongside QCheck, QC Compare, and TQ Analyst in the OMNIC software suite, offers an ideal solution for quality control and assurance of alcohol-based hand sanitizer products.

References and Further Reading

1. J. M. Boyce and D. Pittet, Guideline for Hand Hygiene in Health-Care Settings, Morb. Mortal. Wkly. Rep. 51:1-45, 2002
2. Kampf G, Kramer A. Epidemiologic background of hand hygiene and evaluation of the most important agents for scrubs and rubs. Clin Microbiol Rev. 2004 Oct;17(4):863-93.
3. Policy for Temporary Compounding of Certain Alcohol-Based Hand Sanitizer Products During the Public Health Emergency, Immediately in Effect Guidance for Industry, https://www.fda.gov/
4. Temporary Policy for Preparation of Certain Alcohol-Based Hand Sanitizer Products During the Public Health Emergency (COVID-19), Guidance for Industry, https://www.fda.gov/
5. Guide to Local Production: WHO-recommended Handrub Formulations https://www.who.int/

Acknowledgments

Produced from materials originally authored by Suja Sukumaran and Rui Chen from Thermo Fisher Scientific.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Materials & Structural Analysis.

For more information on this source, please visit Thermo Fisher Scientific – Materials & Structural Analysis.