Raman Spectroscopy: A Powerful Tool For Quality Control Of Sanitizers

INTRODUCTION

In the modern era of technology, Raman spectroscopy has emerged as a sophisticated and flexible tool for conducting quality analysis of a wide range of substances, including solids, powders, and liquids. In this application note, we will focus on the application of Raman spectroscopy in the quality control of sanitizers.

Raman spectroscopy is a quantitative analysis method that offers a quick and reliable way to confirm the ethanol content in hand sanitizers, thereby ensuring their efficacy. This is a non-destructive analytical technique, allowing for repeated measurements without compromising the integrity of the product. Importantly, this method supports unsealing measurement through a transparent container.

Hand sanitizer, a gel-like liquid used to kill microorganisms and disinfect hands, primarily consists of alcohol as its main active constituent. Commercial sanitizers typically contain a compound including ethyl alcohol (ethanol) and isopropyl alcohol (2-propanol). These alcohol compounds become active ingredients in disinfecting hand gels when present in concentrations ranging from 60% to 90%, ensuring an effective fraction of the alcohol content.

METHODOLOGY

Raman spectra collected in the frequency range of 400 to 4000 cm^-1 and a high-quality product should reach over 99%. A known peak at approximately 880 cm^-1 was selected, attributed to the C-C-O symmetric stretching vibration. This peak shifts linearly to higher frequencies as the ethanol concentration increases. In commercial sanitizers, contaminant or adulterant alcohols with different chemical structures, such as methanol and 1-propanol, may be present. The provided article outlines the identified peaks for different types of alcohol. Ethanol is characterized by peaks at 882 cm−1 (C–C stretching), 1049 cm⁻¹ (C–O stretching), 1092 cm⁻¹ (CH3 rocking), and 1454  cm⁻¹ (CH3 bending modes), while ethanol is distinguished by the 1030  cm⁻¹ C–O stretching mode. 2-propanol exhibits peaks at 818  cm⁻¹ (C–C) and 950  cm⁻¹ (C–O stretching modes), while 1-propanol is identified by peaks at 859  cm⁻¹ and 888  cm⁻¹ (C–C stretching) and 968  cm⁻¹ (C–O stretching modes). These distinctive peaks serve as important markers for identifying and analyzing different types of alcohol. These characteristic peaks and their shifts serve as valuable indicators for investigating the quality of sanitizers.

Figure 1. a) Raman spectra of various hand sanitizer products with varying ethanol contents. The inset shows the shifting activities of the C-C-O symmetric stretching mode. b) The comparison of the mode frequency of the CCO symmetric stretching mode on the standard solutions and hand sanitizers.

Spatially offset Raman spectroscopy (SORS)

Traditional and offset spectra, along with their scaled subtraction from a hand-sanitizer solution inside a semitransparent high-density polyethylene (HDPE) container, were analyzed. The traditional spectrum exhibited features from both the polyethylene packaging material (1130 and 1296  cm⁻¹) and the active ingredient alcohol–ethanol (882, 1049, and 1092  cm⁻¹) of the hand sanitizer at similar intensities, while offset Raman is an advanced method allowing a more comprehensive analysis of the sanitizer composition within its packaging (shown in Figure 2).

Figure 2. Schematic representation of the principle of spatially offset Raman.

RAMAN SYSTEM

Raman spectra were obtained using a modular system from Ocean Insight. The QE Pro-Raman provides a product family including preconfigured spectrometers designed for 532 nm, 638 nm, or 785 nm Raman excitation. However, in this application, the excitation wavelength of 785 nm is greater with the decrease of photoluminescence signal, high penetrating intensity, high resolution in organic compounds, and lower heat impacting on samples. The QE Pro-Raman spectrometer was introduced with striking features such as a quantum efficiency of 90%, a scanning range covering 0 - 4429 cm−1, with only 11 cm⁻¹ interval. This spectrometer permits very fast speed analysis with an exposure time of 8 ms. The provided system would include consistent devices consisting of LED, probe, and holder. Furthermore, the final convenient feature is an allowance of both liquids and solids.

CONCLUSION

In conclusion, Raman spectroscopy proves to be an invaluable tool in the pharmaceutical field, particularly in the quality control of sanitizers. The use of Raman spectroscopy, in conjunction with advanced techniques such as spatially offset Raman spectroscopy (SORS), enables accurate and non-destructive analysis of sanitizer compositions within their packaging. Ocean Optics stands out as a leading provider of Raman spectroscopy systems and solutions, it may make it a top choice for researchers and professionals in the field.