What is transmission Raman spectroscopy, or TRS?

Transmission Raman spectroscopy (or TRS) is a form of Raman analysis which is ideally suited for bulk analysis of opaque/turbid materials.  Transmission Raman is based on the collection of Raman light propagating through the sample in the direction of the excitation laser – in essence, the sample is illuminated with the excitation laser from one side, and the Raman signal is collected from the other.  Despite the sample being opaque light from the laser can pass through the sample via light scattering processes.  Many of these photons contain Raman information, and thus transmission Raman spectroscopy is possible.

Unlike traditional Raman spectrometers and microscope systems, the transmission geometry allows true bulk analysis from the entire volume of the sample (for example, a pharmaceutical tablet).

Transmission Raman is non-contact, non-invasive and non-destructive.  It requires no sample preparation. Importantly, the measurement is insensitive to particle size effects, sample homogeneity and orientation.

Transmission Raman spectroscopy can be used to understand:

  • API concentration
  • Content uniformity
  • Polymorphism
  • Crystallinity
  • Powder composition and purity
  • Solid form
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