Quality control of hair, skin, and dentalcare products continues to increase in importance for producers. Aside from safeguarding our health, it is equally important to avoid the sale of out-of-specification products. Product recalls are very expensive and have a lasting effect on a company’s reputation. Therefore, intensive testing of these different care products is essential before they are brought to the market. This article shows how utilizing near-infrared spectroscopy (NIRS) for QC and product screening is the ideal choice for producers of personal care products. Not only is the technique fast and non-destructive, it is also easy to use and does not require any chemicals.
The next sections will introduce various kinds of personal care products followed by an explanation of the NIRS analytical technique and an application example of how NIRS can be used for QC of shampoo and related products.
Shampoos and conditioners are complex mixtures containing detergents, preservatives, and active ingredients (e.g., anti-dandruff compounds). Hair conditioners are composed of a mixture of water and hydrophobic ingredients, forming an emulsion with a specified droplet size. This droplet size varies throughout the different processing steps and is of great importance to control since it affects the performance of the conditioner. As such, the droplet size is a quality parameter that needs to be determined on a regular basis.
Hair gels, waxes, creams, and sprays are cosmetic products used for styling and protecting hair. To obtain the desired properties, many different ingredients are used according to strict formulas. Non-aerosol (i.e., pump) hair sprays mainly contain solvents and copolymers. Some hair creams contain active ingredients to treat dandruff or other issues. In this case, the amount of active compounds in the final product is crucial. Therefore, the concentration of active ingredients must be determined regularly as one of many quality control parameters.
Soap is used for hygiene purposes, either in liquid or solid form. Production of soap starts with saponification, followed by purification to remove impurities and byproducts of the saponification process. When creating solid bars of soap, the raw material is dried and cut into noodles after the purification step. The specification of the finished product depends on the quality of the used soap noodles.
Creams and lotions are applied externally on the skin for various reasons – for example, acting as carriers of active ingredients to assist with their absorption. These products also help to normalize the skin’s moisture levels. Lotions are part of personal care products, cosmetics, or pharmaceuticals and therefore must fulfill stringent quality control requirements. One of the most important quality parameters is water content because it has a major contribution to the texture and moistening characteristics of lotions.
Toothpaste is intended for oral hygiene purposes and needs to fulfill multiple quality requirements to ensure safe usage. Parameters which usually need to be determined include additives, colorants, and active ingredients. The determination of these parameters often requires sample preparation, complex analytical techniques, and chemicals.
Mouthwash is an antiseptic solution intended to reduce the microbial load in the oral cavity. Parameters such as active ingredients, essential oils, colorants, and more must be tested to pass quality control inspections.
Near-infrared spectroscopy (NIRS)—the ideal tool for quality control of hair, skin, and dentalcare products
Near-infrared spectroscopy (NIRS) has been an established method for both fast and reliable quality control of personal care and cosmetics products for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing new methods.
There are several advantages of using NIRS over other conventional analytical technologies. For one, NIRS is able to measure multiple parameters in just 30 seconds without any sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes it an excellent method for the determination of both property types.
For more detailed information about NIRS as a secondary technique, please read our previous blog posts.
ASTM E1655: NIRS as a QC compliant technique
ASTM E1655 (Standard Practices for Infrared Multivariate Quantitative Analysis) is a guide for the multivariate calibration of infrared spectrometers used for determining the physical or chemical characteristics of materials. These practices are applicable to analyses conducted in the near-infrared (NIR) spectral region (roughly 780 to 2500 nm) through the mid-infrared (MIR) spectral region (roughly 4000 to 400 cm-1).
Which parameters and applications are generally possible for NIRS analysis?
Typically, key parameters for the quality control of hair, skin, and dentalcare products such as moisture content, surfactants, active ingredients, iodine value, and total fatty matter (TFM) are determined in the laboratory by chemical and physical methods. These methods not only have high running costs – they are also time consuming.
Near-infrared spectroscopy (NIRS) can overcome these issues as it requires neither chemicals nor sample preparation, provides results in less than a minute, and it can even be used by non-chemists. Furthermore, multiple chemical and physical parameters can be determined simultaneously. The combined benefits of this technology make NIRS the ideal solution for many daily QA/QC measurements or even ad-hoc atline analysis.
Application example: Quality control of surfactants in shampoo with NIRS
Determination of surfactants like sodium laureth sulfate (SLES), cocamidopropyl betaine (CAPB), cocamidopropylamine oxide (CAW), cocamide diethanolamine (DEA), and carbopol in shampoo is a cost- and time-intensive process due to the use of large volumes of chemicals required for these analyses with conventional lab techniques.
To show some of the benefits of using NIRS as a QC tool, shampoo samples were measured with a Metrohm DS2500 Solid Analyzer in transflection mode over the full wavelength range (400–2500 nm). A DS2500 Slurry Cup was employed, which simplifies the positioning of the sample and cleaning of the sample vessel. The 1 mm gold diffuse reflector defines the same pathlength for all measurements to guarantee reproducible results.
The obtained Vis-NIR spectra (Figure 1) were used to create prediction models for the determination of several key ingredients in shampoo. The quality of the prediction models was evaluated using correlation diagrams which display the correlation between Vis-NIR prediction and primary method values (Figure 2). The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis (Figure 2 and Table 1).
Table 1. Concentration ranges and figures of merit (FOM) for key constituents measured in shampoo samples with the DS2500 Solid Analyzer.
This solution demonstrates that NIR spectroscopy is excellently suited for the analysis of multiple active ingredients in shampoo without sample preparation or using any chemical reagents. Additionally, results are obtained in less than one minute, saving users valuable time.
Running costs: Wet chemical methods vs. NIRS
Running costs are significantly lower when using NIR spectroscopy in comparison to wet chemical methods. Comparing running costs of using titration/HPLC with NIR spectroscopy for the determination of key quality parameters in shampoo is illustrated in Figure 3.
Quality control is a critical aspect for the substances we use on our skin and for our dental hygiene. Because of our daily exposure to personal care products, it is critical that they follow industry standards and regulations and are safe to use. Conventional wet chemical analysis of various QC parameters in hair, skin, and dentalcare products involves the use of chemical reagents, skilled chemical analysts, and requires time to prepare and analyze the samples. Near-infrared spectroscopy (NIRS) is a fast alternative, requiring no chemicals or sample preparation steps, and can be used by non-technical personnel. Multiple parameters can be measured at once, further reducing analysis time, and results are delivered in less than a minute.