Hairsprays are actually cosmetic products that are used for styling hair. There are pump hairsprays that predominantly contain copolymers and solvents, which are spread over the hair for setting the hairstyle. In addition to these two key ingredients, the formulation also contains active ingredients that are capable of fighting head lice or dandruff. In order to ensure high efficacy, the right dosing of such active compounds is very important. As a result, these quality parameters should be controlled and the concentration of the active ingredients should be determined regularly.
LC-MS/MS or LC-MS is the main method used to establish active ingredients in liquids, but this method is time-intensive (takes 30 minutes or longer) and also requires chemicals, which can produce waste. Near-infrared spectroscopy (NIRS), on the other hand, is a fast and non-destructive analysis technique that can be used in the routine quality control. NIRS makes it possible to determine the quality of intermediates, incoming materials, and end products in just a few seconds without any need for sample preparation.
For the experiment, a set of customer samples were used that included 15 hairspray samples of 5 batches with the concentration of the active ingredient ranging between 0.0% and 8.4%. About 3g of sample material was first added to the transflection vessel, a gold reflector was then pressed onto the sample within the LiquidKit, and the sample was finally placed into the DS2500 analyzer for the measurement, as shown in Figure 1.
On a DS2500 analyzer, spectra were obtained (see Figure 1) over the entire wavelength range between 400 nm and 2500 nm in transflection mode. This transfection mode operates in such way that the light traversing the sample reflects through the gold reflector back into the detector. The Vision Air Complete software was used to acquire data and develop the quantification method.
Table 1. Used equipment and software
|NIRS DS2500 Analyzer
|LiquidKit for NIRS DS2500
|Vision Air 2.0 Complete
Figure 1. The NIRS DS2500 Analyzer was used for spectral data acquisition over the full range from 400 nm to 2500 nm.
A 2nd derivation was used to pre-heat the spectra and a Partial Least Squares Regression (PLS) was carried out over the spectral regions 2090-2220 nm and 1590–1720 nm. Spectral variations caused by concentration changes of the active ingredient were clearly observed (Figure 2).
Figure 2. 2nd derivative spectra of the hairspray samples with various concentrations of active ingredient ranging from 0.0% to 8.4% in the range 1608-1628 nm. The concentration increases from top to bottom. The selected spectral ranges showed distinct changes with concentration. The traces also compare the acceptable lots (grey traces) with the traces of various concentrations (colored).
When the model was fitted with three factors, it yielded a Standard Error of Cross Validation (SECV) and a Standard Error of Calibration (SEC) of each 0.034%, as shown in Figure 3.
Figure 3. Correlation plot of the active ingredient’s concentration determined by LS-MS and by NIRS.
These results demonstrate that the NIRS technique can be used to accurately establish the concentration of active substances present in hairsprays, and hence can be reliably used in routine quality control for out-of-specification analysis. The NIRS eliminates waste-generating and time-consuming primary analysis techniques, for example, LC-MS.
Using Vis-NIR spectroscopy, active ingredients in hairsprays can be effectively qualified and quantified and hence it can be employed as a high throughput quality control analysis technique to differentiate between the bad lots (containing too low or too high active ingredient concentration) and good lots (with acceptable concentrations of the active ingredient). Compared to standard analysis methods, Vis-NIR spectroscopy solutions provide several benefits – for instance, it does not require any sample preparation, produces reliable results within a matter of seconds, does not generate any waste, and is non-destructive which enables sample re-use.
The above study has been carried out on a DS2500 solid analyzer using the Transflection Kit, but as an alternative, the XDS RapidLiquid Analyzer can also be used to measure the sample in the transmission mode. The benefit of that instrument is that disposable glass vials can be used, which means it is not necessary to clean the measurement window of the DS2500 LiquidKit following each measurement.
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