NIR Spectroscopy in Personal Care and Cosmetics: Enhancing Quality Control and Sustainability

Personal care and cosmetic products permeate almost every aspect of our daily lives. Most people practice daily hygiene before doing anything else, which is why these products are so widely used.

Most personal care products and cosmetics are used for hygienic purposes, to modify appearance, and for general body maintenance. They are primarily applied externally (e.g., on hair, skin, and nails) as well as orally (e.g., on teeth, gums, and tongue); these include soaps, fragrances, lotions, concealer, toothpaste, nail polish, hair dye, ultraviolet (UV) absorbers, and antioxidants.

Personal care products are usually rinsed away immediately after use (e.g., toothpaste or soap), though in some cases, they will not be washed off the body, like when applying sunscreen or hand sanitizer.

Moreover, cosmetics are typically worn on the skin for at least a few hours, for instance when applying makeup, lotion, antiperspirant/deodorant, and other fragrances. Due to their widespread use across the globe, personal care and cosmetic hygiene products are released into the environment in vast quantities after being washed or rinsed away, which can be hazardous for other living organisms.

In Figure 1, the value of the global personal care and cosmetics market for the top five leading countries as of 2020 is displayed.¹ It is expected that this sector will continue growing for the foreseeable.

Figure 1. As of 2020, the United States spent the most on personal care and cosmetic products at nearly 100 billion dollars, followed closely by China ¹. Image Source: Cosmetics Business, Survey by Euromonitor, 2020.

Importance of Quality Control

Good quality control (QC) of personal care and cosmetic products is crucially important, especially given the prevalence of such items in our everyday lives, their frequent contact with our skin, and the impact they can have on the environment after use.

Near-infrared (NIR) spectroscopy is well-suited for the analytical QC of personal care and cosmetic hygiene products, as well as making it an efficient and cost-effective process. Therefore, a short overview of NIRS is presented below, alongside an overview of suitable applications for this industry.

This overview includes examples of how producers of personal care and cosmetics can take advantage of implementing NIRS in the laboratory.

NIRS Technology: A Short Overview

How light and matter interact is a well-documented process. When light is used in spectroscopic methods it is typically described by wavelength or wavenumbers rather than by applied energy.

To generate spectra, A NIR spectrometer (such as the Metrohm DS2500 Liquid Analyzer or DS2500 Solid Analyzer) measures this interaction as shown in Figure 2. NIRS is particularly sensitive concerning the presence of specific functional groups (e.g., CH, NH, OH, and SH). Therefore, NIR spectroscopy is an excellent method for the quantification of certain chemical parameters related to active ingredients, alcohol content, iodine value, water content (moisture), and total fatty matter.

Figure 2. Spectra of hand sanitizer resulting from the interaction of NIR light with the respective samples. Image Credit: Metrohm Middle East FZC

Furthermore, the light-matter interaction depends on the sample’s matrix. This facilitates the detection of physical and rheological parameters, including density and viscosity.

Figure 3. a) Liquid measurements are typically done in vials. b) The measurement mode is known as transmission, where light travels through the sample while being absorbed. Image Credit: Metrohm Middle East FZC

For analyzing creams and viscous substances, the transflection mode is generally recommended. For transflection (Figure 4b), NIR light is transmitted through the sample before being reflected by the diffuse reflector, then it travels back through the sample while being absorbed. The unabsorbed NIR light is then quantified at the end of the analysis.

Figure 4. a) The measurement of creams is typically done in a slurry cup by using a gold stamp as the diffuse reflector. b) The measurement mode is known as transflection, where light travels through the sample, reflects on the diffuse reflector, and travels again through the sample while being absorbed. Image Credit: Metrohm Middle East FZC

For analyzing solid samples like certain detergents, the diffuse reflection mode is considered good procedure. In diffuse reflection (Figure 5b), the sample is illuminated by NIR light, and any unabsorbed NIR light reflects back to the detector.

Figure 5. a) Measurement of solid samples is typically done in sample cups. b) The measurement mode is known as reflection, where the sample is exposed to light and the diffuse reflected light gets absorbed. Image Credit: Metrohm Middle East FZC

The spectra acquisition procedure is shown in Figure 2. This highlights two of the main advantages of NIR spectroscopy: simplicity and speed.

The main advantages of NIR analyses are listed below:

• Rapid measurement technique – results generated in under a minute.
• Sample preparation not required – solids and liquids can be used in true form.
• Low cost per sample – no chemicals or solvents required.
• Environmentally-friendly – no waste produced.
• Non-destructive – preserves precious samples for reused after analysis.
• Easy to operate – user friendly system.

For more additional information regarding NIRS as a secondary technique, please follow the links below.

Benefits of NIRS: Part 1

Benefits of NIRS: Part 2

Benefits of NIRS: Part 3

Benefits of NIRS: Part 4

Regulations for Personal Care and Cosmetic Products

While regulations for personal care and cosmetic products are generally not as stringent as those for pharmaceuticals, there are similar trends. Thus, NIRS is a technique suitable for use in regulated markets as Metrohm NIRS analyzers comply with USP <856>, and the Vision Air complete package falls within 21 CFR Part 11 compliance guidelines.

To learn more about NIRS compliance with 21 CFR Part 11, click the link below.

NIR spectroscopy: a 21 CFR Part 11 compliant tool for QC and product screening

Which ASTM Test Method Makes NIRS a QC Compliant Tool?

Infrared spectrometers used for determining physical or chemical characteristics of materials can be calibrated following the guidance of ASTM E1655 (Standard Practices for Infrared Multivariate Quantitative Analysis) for multivariate calibration.

These are applicable to analyses being performed in the near-infrared (NIR) spectral region (somewhere between 780 to 2500 nm) to the mid-infrared (MIR) spectral region (approximately 4000 to 400 cm^-1).

Applications and Parameters for QC of Personal Care and Cosmetic Products with NIRS

Standardized test methods are often used to identify the precise chemical, physical, and tribological properties of personal care products and cosmetics. Laboratory testing is a crucial part of R&D and QC.

The following test parameters are key for a number of end products in this industry, and can be reliably measured using NIRS (Table 1).

Table 1. Application examples using NIRS for QC of selected personal care and cosmetic products. Source: Metrohm Middle East FZC

References

1.  Cosmetics Business; Euromonitor. Global Major Beauty and Personal Care Market 2020.

This information has been sourced, reviewed and adapted from materials provided by Metrohm Middle East FZC.

For more information on this source, please visit Metrohm Middle East FZC.