- Data Collection
A Brimrose Free Space spectrometer was used to collect absorbance spectra of five samples containing additives. Each sample was placed in a large petri dish and leveled out. The instrument was tested and adjusted for maximum signal. 200 scans were collected for each reading and averaged into one spectrum. As the instrument was scanning, the petri dish was moved back and forth and around in circles to allow the instrument to scan the entire surface of the sample contained in the dish. The samples were kept at the objective distance of 40 mm. 5 spectra were taken for each sample for a total of 25 spectra. All raw spectral data was taken in reflectance mode with 2nm resolution. Wavelength range was between 1100nm and 2300nm. Spectra were processed into absorbance and first derivative and imported into Unscrambler for modeling.
Figure 2. Absorbance spectra of all 5 samples containing additives.
The spectra show clear peaks around 1200, 1400, and 1550 nm. The loading weights for the PCA analysis will confirm that these peaks can be used to distinguish between these 5 compounds and could also probably be used for quantitative analysis of additive level in these compounds.
Figure 3. Absorbance spectra of sample PPM 11174
Figure 4. Absorbance spectra of sample PPM11421E63
Figure 5. Absorbance spectra of sample PM 11025E4
Figure 6. Absorbance spectra of LDPE RESIN
Figure 7. Absorbance spectra of PP RESIN
2.Modeling and Regressions
PCA analysis was performed on the absorbance spectra using Unscrambler. PCA analysis was also performed on the first derivative spectra but the results were much better using the absorbance data. The PCA analysis shows that all 5 samples can be clearly distinguished from one another using the Brimrose spectrometer and that the information used to distinguish the samples from one another comes from the wavelength ranges where the spectral peaks occur.
Figure 8. Scores plot for PCA analysis of all 5 sample sets.
Figure 9. X-Loading weights plot for PCA analysis of 5 samples.
The scores plot shown in Figure 8 shows that the Brimrose Free Space Luminar 2030 is able to distinguish between all 5 samples in this study. The 5 sets of data points are clearly separated from one another. Figure 9 shows that the information used for separating the samples using the spectra comes from the same wavelength ranges where the spectra peaks occur. Both the absorbance spectra and the loading weights have peaks around 1200, 1400, and 1550 nm. This is a good indication that these peaks contain the spectral information necessary to create a regression model that could quantify the amount of additive in the samples.
V. Conclusions and Recommendations
It is concluded that the Brimrose Free Space spectrometer can be used to qualitatively analyze the 5 samples used in this study. There are clear spectral differences that can be seen from looking at the spectra and the PCA analysis makes it even clearer that the five samples can be distinguished using spectral data. The fact that the PCA analysis takes its information from the same wavelengths where the spectral peaks occur indicates that these peaks can probably be used to quantify the amount of additive found in these samples. It is recommended that Brimrose receive quantities of the same samples with known different amounts of additives. Brimrose will conduct a similar study collecting spectral data and using the data for PLS1 analysis, which will show if it is feasible to set up a model to quantitatively analyze the amount of additives in the samples.