• Non-destructive method
• Non-contact
• Typically no sample preparation ? no need to dissolve
  solid samples, or destroy physical and chemical properties
  prior to analysis
• Easy sampling through glass and plastic packaging
• Easy access to far-infrared vibrations
• Raman active bonds typically not strongly affected by
  molecular interactions, making the Raman spectrum less
  susceptible to associated band broadening and shifting.
  This results in a spectrum that is more amenable to
  spectral interpretation and successive subtraction

Raman spectroscopy has major advantages over other analytical techniques. The most important advantages are the ease of sample preparation and the rich information content.

Raman is a light scattering technique, so all that is required for the collection of a spectrum is to place the sample into the excitation beam and collect the scattered light.

There are few concerns with sample thickness (as in transmission analyses) and little contri­bution from the ambient atmosphere, so there is no need for high-vacuum or desiccated sample holders. Glass, water and plastic packaging each have very weak Raman spectra, making the technique even easier to use. Often, samples can be analyzed directly inside the glass bottle or plastic bag without opening the package and risking contamination. Aqueous samples are readily analyzed without the need to remove water, and because ambient humidity is not a problem, there is no need to purge the instrument.

Simplfied energy level diagram. A molecule at rest resides in the ground vibrational and electron states. A laser-generated electric field raises the energy of the system by inducing a polarization in the chemical states (virtual state). Relaxation from the vitual state reulsts in Rayleigh scatter. Stokes-Raman shift scatter is of lower energy (longer wavelength) than the laser light.

Furthermore, no two molecules give exactly the same Raman spectrum, and the intensity of the scattered light is related to the amount of material present. This makes it easy to obtain both qualitative and quantitative information about the sample, allowing for spectral inter­pretation, library searching, data manipulations and the application of quantitative analysis computer methods.

Raman spectroscopy is non-destructive. There is no need to dissolve solids, press pellets, compress the sample against optical elements or otherwise alter the physical or chemical structure of the sample. Thus, Raman has been used extensively for analysis of such physical properties as crystalllnity, phase transitions and polymorphs. The lack of sample preparation also minimizes cleanup and the possibility of cross-contamination.

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Raman Spectrometers from Thermo:

• Nicolet NXR FT-Raman Spectrometers 
• Nicolet Almega XR Dispersive Raman Spectrometer