Determination of sodium laureth sulfate (SLES), cocamidopropyl betaine (CABP), 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 per analysis.
This application note demonstrates that the DS2500 Solid Analyzer operating in the visible and near-infrared spectral region (Vis-NIR) provides a cost-efficient and fast solution for a simultaneous determination of sodium laureth sulfate (SLES), cocamidopropyl betaine (CABP), cocamidopropylamine oxide (CAW), cocamide diethanolamine (DEA), and carbopol in shampoo. With no sample preparation or chemicals needed, Vis-NIR spectroscopy allows for the analysis of these parameters in less than a minute.
Shampoo samples were measured with a 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 path length for all measurements to guarantee reproducible results. As displayed in Figure 1, samples were measured without any preparation. The Metrohm software package Vision Air Complete was used for all data acquisition and prediction model development.
Equipment | Metrohm number |
---|---|
DS2500 Solid Analyzer | 2.922.0010 |
DS2500 Slurry Cup | 6.7490.430 |
Gold Diffuse Reflector 1 mm | 6.7420.000 |
Vision Air 2.0 Complete | 6.6072.208 |
The obtained Vis-NIR spectra (Figure 2) were used to create prediction models for quantification of the sodium laureth sulfate (SLES), cocamidopropyl betaine (CABP), cocamidopropylamine oxide (CAW), cocamide diethanolamine (DEA), and carbopol in shampoo. The quality of the prediction models was evaluated using correlation diagrams, which display the relationship between Vis-NIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.
Result sodium laureth sulfate
Figures of merit | Value |
---|---|
R2 | 0.998 |
Standard error of calibration | 0.13% |
Standard error of cross-validation | 0.14% |
Result cocoamidopropyl betaine
Figures of merit | Value |
---|---|
R2 | 0.996 |
Standard error of calibration | 0.04% |
Standard error of cross-validation | 0.05% |
Result cocoamidopropylamine oxide
Figures of merit | Value |
---|---|
R2 | 0.998 |
Standard error of calibration | 0.031% |
Standard error of cross-validation | 0.058% |
Result cocoamide diethanolamine
Figures of merit | Value |
---|---|
R2 | 0.998 |
Standard error of calibration | 0.034% |
Standard error of cross-validation | 0.036% |
Result carbopol
Figures of merit | Value |
---|---|
R2 | 0.969 |
Standard error of calibration | 0.290% |
Standard error of cross-validation | 0.410% |
This application note demonstrates the feasibility of NIR spectroscopy for the analysis of sodium laureth sulfate (SLES), cocamidopropyl betaine (CABP), cocamidopropylamine oxide (CAW), cocamide diethanolamine (DEA), and carbopol in shampoo. In comparison to wet chemical methods running costs are significantly lower when using NIR spectroscopy (Tabel 7 and Figure 8).
Lab method | NIR method | |
---|---|---|
Number of analyses per day | 10 | 10 |
Cost of operator per hour | $25 | $25 |
Costs of consumables and chemicals (SLS, CABP, CAW, DEA, carbopol) | $5 | $1 |
Time spent per analysis (SLS, CABP, CAW, DEA, carbopol) | 5 min | 1 min |
Total running costs (per year) | $18,188 | $2,063 |