Raman spectroscopy holds great promise and potential which awaits exploitation in the hands of the pharmaceutical analyst. Raman spectra complement the findings of IR spectroscopy. Raman activity results from change in polarizability of the molecule unlike IR which results from change of dipole moment of the molecule. This therefore enables analysts using Raman technique to extend analysis to homo – atomic molecules.
Major applications in pharmaceutical analysis
- Quantification of active pharmaceutical ingredients
- Polymorphic form identification. The polymorphic state of the ingredient may get altered during manufacture or scale up operations. Since the form affects both solubility and efficacy it is important to monitor changes if any in the polymorphic form
- Evaluation of raw materials including polymeric coatings
- In combination with a microscope Raman spectroscopy provides valuable information through surface imaging.
Advantages of Raman Spectroscopy
Raman spectroscopy offers several distinct benefits and can be used to study all types of samples ranging from solids, liquids, powders, gels, slurries and aqueous solutions. Studies can be carried out in-situ without need for sample preparation. Using the technique it is possible to analyze formulations in different packs such as blister packs, sachets, glass vials or polymeric containers. This feature is particularly useful in a pharmaceutical laboratory as it offers the following specific advantages :
- Analysis of samples which would degrade due to exposure to moisture, heat or light
- The polymorphic state of active ingredient may change due to sample processing
- To prevent the chemist from toxic nature or unpleasant odour of the formulation
- Higher analysis throughput due to is saving on time required for sample processing and preparation
Raman spectroscopy has also potential for process monitoring applications using fibre optic probes which permit Raman instrument to be located away from the sampling point.
The disadvantages of the technique are relatively higher cost of the Raman spectrometer and inherent interference of the Raman signals by stray light from Rayleigh scattering. This problem has been overcome to a large extent in present-day spectrometers.