Traditional Raman spectrometers provide high resolution spectra using tightly focused beams resulting in small area of interrogation. Due to their inability to spatially target all components, they are ineffective in analyzing a sample with varying composition (heterogeneous substances).
Figure 1. Instrumental diagram of the ORS mechanism
Increasing the area of interrogation with a larger spot leads to lower resolution and loss of valuable spectral information. Therefore, the use of Raman spectrometers is limited by its unsuitability for heterogenous substances and also sampling issues like laser-induced degradation.
Application of ORS in Assessment of Heterogenous Samples
ORSTM technology is capable of delivering high spectral resolution across large sample area using rastering, a process of quickly moving a tightly focused laser beam over a large area. This is particularly useful in the analysis of effervescent cold medicines containing multiple active ingredients in each heterogeneous tablet.
While traditional identification and verification techniques requires the collection of several spectra at different points on the tablet, Mira spectrometers equipped with ORS technology can capture a large interrogation area in a very short time.
This technology enables better representation of the identity of a sample, rather than its composition, and also reduces the inconsistencies in the spectral details during the assessment of heterogeneous materials. Therefore, Metrohm Instant Raman Analyzers (Mira) spectrometers equipped with ORS technology are capable of analyzing all of the ingredients in a single scan.
Experimental Design and Method
Spectral data of heterogenous sample (Equate Effervescent Cold Relief) tablets were obtained with turning the ORS OFF at first and then with ORS ON. The sampling of these hygroscopic tablets was performed by obtaining fresh samples immediately upon removing them from the foil wrapper fresh samples every half hour.
The spectra were then averaged in each case and the spectral variance was determined to demonstrate the quality and convenience of a single ORS scan. Following the initial experiment, a final experiment was performed to compare two competing effervescent cold medicines (Equate Effervescent Cold Relief Tablets and Alka-Seltzer Plus Cold Formula) using Mira P with ORS technology and verification supported by p-values. Spectral information was obtained from various areas of each tablet.
In each of these experiments, 60 ORS OFF measurements with varied integration times between 1s and 10s in order to observe variation in the spectra were taken. This sample set was used to obtain a single, averaged spectrum, which was compared to a single EQ spectrum collected with the ORS ON. MiraCal software was used to acquire and process spectral data.
|Excitation wavelength (nm)
The results from the spectral overlay of the average of 60 spectral measurements at ORS OFF setting to a single measurement at ORS ON revealed that a single scan with the ORS ON showed great similarity. Therefore, ORS technology can produce reliable representative spectra, at a significantly less sampling time. The results obtained from the second experiment demonstrated by the p values showed that the two effervescent cold medicines tested were different in composition even though they showed visual similarities in spectrum.
Figure 2. Overlay of 60 ORS OFF spectra
Figure 3. Reduced ORS OFF spectra
Figure 4. EQ ORS OFFavg/ON comparison
Figure 5. Overlaid EQ and AS spectra
Taken together, Mira P equipped with ORS technology is a powerful tool to obtain accurate spectral data for chemical identification and verification, especially for the assessment of heterogenous samples. Unlike traditional Raman methods that require multiple measurements of heterogeneous samples to obtain a representative spectrum the, Mira P with ORS technology provides accurate and representative spectra with only one measurement, saving both time and effort.
This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.
For more information on this source, please visit Metrohm AG.