FTIR (Fourier Transform Infra-Red) and Raman spectroscopies both involve vibrational and rotational energy levels, but offer complementary information. FTIR is a direct absorption process and Raman spectroscopy is a scattering process. These have different rules governing their occurrence, and thus offer differing sensitivies to functional groups. As an example, carbonyl groups are always strongly IR active whereas aromatic rings and carbon double bonds have strong Raman bands. Besides the sensitivity for different functional groups, the combination allows researchers to benefit from the advantages of both techniques:

Advantages of FTIR:

• well-known technique
• large analytical base
• high sensitivity
• independent of the sample’s fluorescence

Advantages of Raman:

• high spatial resolution (<1 μm) with true confocality
• access to low frequencies
• no sample preparation
• ability to analyse through glass vials, and within aqueous solution

Combined Raman-FTIR systems such as the LabRAM IR² eliminate the difficulties and cost of having two separate systems and saves significant space without loss of performance. Time is saved by allowing the operator to quickly make both Raman and FTIR measurements, without the need to transfer the sample and then relocate the measurement point. Thus the user can have complete vibrational characterisation of a sample, benefiting from the advantages of both FTIR and Raman spectroscopy.