What is Raman Spectroscopy?
Raman Spectroscopy is a non-destructive chemical analysis technique which provides detailed information about chemical structure, phase and polymorphic, crystallinity and molecular interactions. It is based upon the interaction of light with the chemical bonds within a material.
Raman is a light scattering technique, whereby a molecule scatters incident light from a high intensity laser light source. Most of the scattered light is at the same wavelength (or color) as the laser source and does not provide useful information – this is called Rayleigh Scatter. However, a small amount of light (typically 0.0000001%) is scattered at different wavelengths (or colors), which depend on the chemical structure of the analyte – this is called Raman Scatter.
A Raman spectrum features a number of peaks, showing the intensity and wavelength position of the Raman scattered light. Each peak corresponds to a specific molecular bond vibration, including individual bonds, such as C-C, C=C, N-O, C-H etc., and groups of bonds ,such as benzene ring breathing mode, polymer chain vibrations, lattice modes, etc.
A typical Raman spectrum, in this case, of amphetamine.
Information provided by Raman spectroscopy
Raman's spectra of ethanol and methanol, showing the significant spectral differences, which allow the two liquids to be distinguished.
Raman's spectroscopy probes the chemical structure of a material and provides information about:
- Chemical structure and identity;
- Phase and polymorphism;
- Intrinsic stress/strain;
- Contamination and impurity.
Typically, a Raman spectrum is a distinct chemical fingerprint for a particular molecule or material, and can be used to very quickly identify any drugs, or distinguish them from others. Raman spectral libraries are often used for identification of a material based on its Raman spectrum – libraries containing thousands of spectra are rapidly searched to find a match with the spectrum of the analyte.
The general spectrum profile (peak position and relative peak intensity) provides a unique chemical fingerprint which can be used to identify a material, and distinguish it from others. Often the actual spectrum is quite complex, so comprehensive Raman spectral libraries can be searched to find a match, and thus provide a chemical identification.
The general spectrum profile (peak position and relative peak intensity) provides a unique chemical fingerprint which can be used to identify a material, and distinguish it from others. Often the actual spectrum is quite complex, so comprehensive Raman spectral libraries can be searched to find a match, and thus provide a chemical identification.
Identifying functional groups within molecules
The vibrations of certain distinct subunits of a molecule, called its functional groups, will appear in a Raman spectrum at characteristic Raman shifts. Such a shift is similar for all molecules containing the same functional group. These signals are particularly useful when monitoring reactions which involve these functional groups (oxidation, polymerization, etc.), since they provide a direct measure of the progress during the reaction.
Raman strum of benzonitrile and the stretching vibration of the cyano-group (CN) of benzonitrile at 2229.4 cm-1 (red).
Raman strum of benzonitrile and the stretching vibration of the cyano-group (CN) of benzonitrile at 2229.4 cm-1 (red).
Using these characteristic shifts makes it possible to relate the spectrum of an unknown compound to a class of substances, for example the stretching vibration of the carbonyl group in an aldehyde is always in the range of 1730 cm–1 to 1700 cm–1. The image above demonstrates the Raman spectrum of benzonitrile containing the stretching vibration of the cyano-group (CN) of benzonitrile at a characteristic value of 2229.4 cm-1.
Drug analysis with handheld Raman spectrometery
There are necessities to rapid qualitative and quantitative determination of substances today. These problems concern people, who work with drugs producing or resell them. Fortunately, these issues can be solved by handheld raman spectrometery.
Handheld Raman spectrometers are used to provide direct sampling of loose solid or liquid material or to conduct sampling on a containerized sample. These devices are rugged, field-portable units that are designed to provide responders with the ability to analyze unknown powders and liquids without destroying the sample.
Method opportunities
First, you can check conformity of your substances with the spectrometer database. Consumers can manually produce a database with different drugs and substances with different concentration or buy database and install in the own device. According to the database, concentrations of interesting substances could be measured.
There are pictures of a typical spectrometer device, a vial for test samples and a cuvette. Attach the cuvette with inserted vial with a sample and close cuvette. It is important for providing analysis without light pollution.
There are pictures of a typical spectrometer device, a vial for test samples and a cuvette. Attach the cuvette with inserted vial with a sample and close cuvette. It is important for providing analysis without light pollution.
Advantages:
- Handheld raman allow getting analysis report with quite high accuracy of structure and concentrations (in case you have a special library) without destroying a sample.
- You can provide experiment instantly without additional materials.
- Easy to understand and friendly interface.
- Cannot get accurate results for all contaminants in the sample. For instance, sides substances of amphetamine, which could be determined by GC-MS analysis.
- Cannot determine mix of substances as heroine, ecstasy or very low amount substances (DMT, NBOME, LSD etc.) because they are sold with paper or side materials for tablet forms.
Conclusion
Raman spectroscopy is a powerful method of analytical chemistry. This method can be a solution for drug manufacture problems with determinating substances by helps of portable form, which has some advantages and disadvantages. Although price for this device razer high, this instrument can allow controlling your products for keeping appropriate quality and hold your brand on the highest market level.
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