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Spectroscopy is the study of the interaction between radiation and matter using means of wavelength. Spectrum analysis is the use of the absorption, emission, or scattering of radiation by matter to qualitatively or quantitatively study the matter or to review physical processes. The matter is atoms, molecules, atomic or molecular ions, or solids.
Raman Spectroscopy named after the Indian Scientist C.V. Raman is a technique commonly used in chemistry to obtain a structural fingerprint of chemical molecules by which they can be identified uniquely.
It depends upon inelastic scattering of photon, known as Raman Scattering. The name 'Raman spectroscopy' typically refers to the concept of vibrationalRaman using laser wavelengths which are not absorbed by the sample. Many variations of Raman spectroscopy are used for various scientific purposes such as surface-enhanced Raman, resonance Raman, tip-enhanced Raman, polarized Raman, stimulated Raman, transmission Raman, spatially-offset Raman, and hyper Raman.
All the qualitative analysis techniques have been wide explored for the pharmaceutical applications.
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For years Raman Spectroscopy is an established qualitative analysis technique for quantitative analysis of molecular materials of all sorts as a result of it's a non-contact characterization methodology that doesn't need any sample preparation.
In various areas of the pharmaceutical industry, Raman spectroscopy is gaining popularity. Unlike IR spectroscopy, it also provides information on the simple vibrational bands providing a high degree of analytical precision. It is also an appropriate addition to current analytical methods such as NMR, MS and elemental analysis. In the pharmaceutical industry, Raman spectroscopy has enormous potential.
The rapid identification of compounds in the analysis of drug mixtures, active ingredients and excipients, the identification of contaminants, the characterisation of formulated materials and the understanding of the processes of blending involving pharmaceutical formulations are accessible using Raman Techniques.
One possible Raman Spectroscopy setup is shown in the below image. A source of monochromatic light, generally obtain from a laser in the visible, near infrared or near UV range is used. The laser interacts with molecular vibrations resulting in the energy of the laser photons being varied up or down while they return to the detector.
Typically, a sample is illuminated with a laser beam. Electromagnetic radiation from the illuminated spot is collected with a lens and sent through Focussing optics (monochromator). Elastic scattered radiation at the wavelength corresponding to the laser line is filtered out by either a notch filter, edge pass filter, or a band pass filter, while the rest of the collected light is dispersed onto a detector
In pharmaceutical laboratories, Raman instruments are more commonly used. Technological progress over the past decade has resulted in the production of much smaller Raman spectrometers requiring only one tablet of laboratory space
The topic of this paper is a very popular and interesting one, which has a lot of research done on it. The literature I had referred to while writing this paper are the following:
Before moving on to the application of Raman Spectroscopy in medical sciences specifically in pharmaceuticals, let us first understand the theory behind it.
The Raman effect occurs when light hits a molecule and interacts with that molecule's electron cloud and bonds. A photon excites the molecule from the ground state to a simulated state of energy for the spontaneous Raman effect. This returns to a particular rotational or vibrational state when the molecule absorbs a photon and returns to the ground state. The energy difference between the original state and this new state results in a shift away from the excitation frequency in the direction of the emitted photon.
For a molecule to exhibit a Raman effect, a change in the potential for molecular polarization or amount of deformation of the electron cloud with respect to the vibrational coordinate is required. The amount of the change in polarizability will determine the intensity of Raman scattering. A vibrational band's position and intensity are characteristic of the underlying molecular motion and consequently of the atoms involved in the chemical bond, its conformation, and its immediate environment.
There are various types of Raman Scattering:
First, a photon interacts with a molecule in Rayleigh Scattering (elastic scattering), polarizing the electron cloud and elevating it to a 'virtual' state of energy. This is extremely short lived (10-14 seconds in order) and the molecule will soon fall back to its ground state, releasing a photon. In any direction, this can be released, resulting in scattering. The energy released in the photon must be the same as the energy from the original photon, though, since the molecule falls back to the same state it began in. The dispersed light therefore has the same wavelength.
Therefore, Rayleigh scattering does not contain any information about the sample's vibrational energy levels. Raman Scattering is unique because it is inelastic. During the scattering process, light photons lose or gain energy and thus experience an increase or decrease in wavelength respectively. If the molecule is promoted from a ground to a virtual state and then falls back to a vibrational state (higher energy), then the dispersed photon has less energy than the incident photon, and thus a longer wavelength. This is called Stokes scattering.
If the molecule is in a vibrational state to begin with, and is in its ground state after scattering, then the scattered photon has more energy, and thus a shorter wavelength. This is called Anti-Stokes scattering.
Usually, Raman shifts are stated in wavenumbers with units of inverse length, as this value is directly related to energy.The following equation can be used to convert between spectral wavelength and shift wavenumbers in the Raman spectrum: where is the Raman shift expressed in wavenumber(cm-1), is the excitation wavelength, and is the Raman spectrum wavelength.
Major technological and scientific innovations in the past 10–15 years have significantly broadened the applicability of Raman spectroscopy in chemical analysis.
The applications of Raman Spectroscopy can be simplified as:
Reliable monitoring of pharmaceutical manufacturing operations requires knowledge of a drug formulation's physical and chemical characteristics throughout all of its unit operations. For this reason, pharmaceutical researchers have recognized the usefulness of non-destructive Raman methodologies as a potential tool for use in advanced process analysis schemes to assess pill, drug content and track transitions of polymorphism.
It was figured out that RS can be used in the qualitative, non-invasive analysis of the bulk content of the pharmaceutical products found in capsules of the production line. Raman spectroscopy using NIR excitation demonstrated significant potential as a rapid quality control tool for pharmaceutical samples.
RS can be used as an online tool for tracking product hydration during drying, hydrate formation during high shear wet granulation, wax bead mixing API, polymorphic turnover kinetics.
It also demonstrates some benefits over conventional substance IR analysis. It is possible to use Raman spectroscopy to differentiate pharmaceutical crystal forms of the solid state. The essence of crystal formation can be analysed or a qualitative crystal form analysis can be done with the use of advanced sampling accessories.
Some of the Raman Active samples, which are certified and studied by Raman Spectroscopy are: Acebutolol, Fluocortolone, Isosorbide, Alprenolol, , Amoxycillin, Amphetamine, Nicotinamide, Spironolactone, Amphotericin A/B, Arterenol, Acetaminophen, AmilorideTriamterene, carbonate and glycine, Cimetidine, Ciprofloxacin , Cocaine , Diclofenac, Fluconazole, Strychnine, Sulfamerazine, Sulfadiazine etc
Although the idea of chemotherapeutics based on synthetic oligonucleotides was introduced several years ago, there is an ongoing effort to seek their satisfactory chemical layout. It has been found that Raman spectroscopy is an appropriate method for analyzing some key properties of new analogs of synthetic nucleic acid. A Swedish Chemist cum Scientist Hanu’s studied the impact of the isopolar shortened internucleotide linkage modification to hybridization properties of potential antisense or antigene oligonucleotides by using a model molecular system consisting of polyuridylic acid and analogues of diadenosinemonophosphate with the modified linkage. Raman spectra indicate the decrease in their compatibility with the natural nucleic acid chain.
Based on FT-Raman spectroscopy and PLS regression, a quick and simple method for quantitative analysis of monoclinic (form I) and orthorhombic (form II) paracetamol has been developed. The multivariate calibration proposed significantly improved the quantification methods for paracetamol polymorphs over existing methods. RS, in conjunction with adequate mathematical / statistical data analysis and modeling, has proved useful in defining and quantifying the polymorphic types of the product
In the analysis of formulated tablets of pharmaceutical interest, various experimental FT-Raman imaging procedures and their ability to obtain and spatially resolve chemical information are available. The behaviour, stability and texture of emulsions are strongly affected by their microstructure, so there is a need for an effective method of chemical imaging.
A scientist named JJ Andrew used Raman imagery to distinguish inherently low contrast multi-component complex, multi-phase emulsion systems. He explained how to create high-resolution, three-dimensional maps of the chemical composition of heterogeneous and multi-phase materials using a confocalRaman microscope with an automated level. Several commercial product systems have been characterized, ranging from pharmaceutical and skin creams to toothpaste. For solid dispersions, in an amorphous state, the substance becomes stored in the polymer carrier. Recrystallisation can affect the carrier's therapeutic quality under pressure conditions.
ConfocalRaman spectroscopy was used to analyse solid dispersions of ibuprofen anti-inflammatory agent. It was found out that confocalRaman spectroscopy can analyse different layers (e.g. tablet coatings), areas (e.g. phase separation) and actually combining performance in a manufacturing process that is of great industrial significance. For the Raman image analysis of pharmaceutical tablets, generalized 2D correlation spectroscopy was used to reveal molecular interactions between chemical components. It was possible to evaluate synchronous and asynchronous correlation by using a spatial range as a perturbation factor in 2D correlation scheme.
The polymorphic nature of drugs is a major concern of the pharmaceutical industry as it may have important manufacturing, clinical, legal and commercialimplications.4,6–8 Thus, it is crucial that various polymorphic types of drugs can be properly defined and quantified.
Because polymorphic types are generally extremely resistant to physical treatments such as mulling, grinding or heating, most chemical-physical techniques are not useful in the analysis of substances that can undergo polymorphic transformations.
The main advantage of Raman spectroscopy is that no sample manipulation is needed and thus the spectra can be obtained with complete certainty of the identity of the sample under examination in the case of polymorphs that are susceptible to transformation. The absence of sample preparation, either way, makes Raman spectroscopy a more robust test procedure.
For successfully evaluate mixtures with differing ratios of beta and delta mannitolpolymorphs, a quantitative approach using FT-Raman spectroscopy was used.
Mannitol is a polymorphic excipient commonly used as the beta form in pharmaceutical products, although other polymorphic substances (alpha and delta) are common contaminants. For quantifying the concentration of the beta form using FT-Raman spectroscopy, binary mixtures containing beta and delta mannitol are prepared.
The characteristic spectral regions of each type were selected and the peak intensity ratios between beta peaks and delta peaks were determined. A correlation curve was developed using these ratios, which was then checked by further analysis of known composition samples. The differences exhibited by the FT-Raman spectra of the beta and delta mannitol were used to successfully identify and quantify polymorphic mixtures.
The results indicate that levels down to 2% beta could be quantified using this novel, non-destructive approach. Potential errors associated with quantitative studies using FT-Raman spectroscopy were also researched.
Advantages of Raman Spectroscopy in Pharma Industry
Limitations of Raman Spectroscopy in Pharma Industry
Vibrational spectroscopy is an excellent method of substance identification because it provides unique fingerprint spectra for each specific compound. Of the different vibrationalspectroscopies available, Raman spectroscopy may be the first-choice approach because the spectrum it provides is rich in details and it involves practically no planning for samples.This makes it ideal for analysing tablets, powders and liquids, thereby avoiding mechanical changes during sample preparation that could alter the formulation's physicochemical properties.
Raman spectroscopy has been proven to be a versatile tool in pharmaceutical and biopharmaceutical applications. Raman spectroscopy is also used in a variety of ways in the pharmaceutical laboratory. The technique measures particle density through the intensity of the Raman spectra at the most basic level. With additional information given by Raman spectroscopy, conventional characterization of the product material is improved and quantitative polymorph assays can be produced.
Raman can also be used to support pharmaceutical development qualitatively and semi-quantitatively.
Although Raman spectroscopy shows advantages over the more traditional IR spectroscopic techniques, it should not be considered as the only analytical technique to solve most problems, but as one more powerful, though expensive, technique that is part of a multidisciplinary approach to analysis.
Application of Raman Spectroscopy in Pharmaceuticals. (2024, Feb 20). Retrieved from https://studymoose.com/document/application-of-raman-spectroscopy-in-pharmaceuticals
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