Fourier Transformed Infrared Spectroscopy (FTIR)

Fourier Transformed Infrared Spectroscopy
Simple FTIR spectrum contrasting raw measurement (blue) to reference (red) on HVAC sample

Fourier-transformed infrared spectroscopy (FTIR) is a nondestructive, optical technique used to analyze chemical composition and the optical properties of a material.

  • Rapid results
  • Nondestructive analysis
  • Particularly well suited for organic chemical analysis
  • Robust reference libraries are available
  • Requires reference or a standard / control sample to make positive chemical identifications
  • Most inorganic molecules do not exhibit an FTIR spectrum
Example Outputs

FTIR spectra from 3 plastic polymer materials – Polyethylene terephthalate (PET), Polyethylene (PE), Polypropylene (PP) – overlaid for comparison

Simple FTIR spectrum contrasting raw measurement (blue) to reference (red) on HVAC sample

Instruments Used for FTIR
Thermo Scientific Nicolet iS50 IR Spectrometer

Thermo Scientific Nicolet iS50 IR Spectrometer

  • Motorized and automated beamsplitter exchange
  • Multiple Detectors with Flexible Spectral Range:
    • Standard: 7800 – 350 cm-1
  • Mid-IR Optical Resolution: < 0.09 cm-1
  • Wavenumber Accuracy: better than 0.005 cm-1
  • Flexible Analytical Modes
  • View Instrument Brochure
Thermo Scientific Nicolet Continuum IR Microscope

Thermo Scientific Nicolet Continuum IR Microscope

  • 32x magnification
  • Multiple detector options:
    • Narrow-band MCT-A: High performance 11700 – 750 cm-1
    • Medium-band MCT-A: 11700 – 600 cm-1
    • Wide-band MCT-B: 11700 – 450 cm-1
  • Sampling Modes: transmission, reflection, grazing, and ATR
  • View Instrument Spec Sheet
Thermo Fisher Nicolet 6700 IR Spectrometer

Thermo Fisher Nicolet 6700 IR Spectrometer

Sample Requirements
  • Solid or liquid phase
  • Flat surface is ideal; other topographies are accepted, may impact data quality
  • Material must not be too reflective (e.g. high-reflection metallics), nor too transmissive (e.g. some glasses), for best results
How FTIR Works

In an FTIR measurement, an initially wide range of infrared wavelengths are simultaneously shone upon an area of the sample.

Using an interferometer, the FTIR system then extracts a specific wavelength band at a time and measures its light intensity: selectively detecting either reflected or transmitted beams. The operator will determine whether to target transmittance or reflectance intensity based on the sample’s composition and topography. After this initial measurement, the extracted wavelength band is subsequently scanned over the entirety of the wavelength range, capturing an intensity measurement at each band. The resulting values are then fourier-transformed to produce the initial sample spectrum.

To isolate the real sample spectrum, a reference – or ‘blank’ – trial is conducted without any material inserted in the beam path. This spectrum is used to normalize the sample spectrum and to isolate the relevant specimen information from the total signal.

In the wavelength range of interest, different types of chemical bonds absorb at different wavelengths: providing a spectral signature which is material dependent. The resulting background-subtracted spectrum can then be used to qualitatively identify chemical functional groups and trace chemicals present in the specimen.

ATR-FTIR is a variant FTIR measurement mode which uses a specialized crystal to generate multiple internal reflections along the lateral dimension of the sample, increasing signal-to-noise and surface sensitivity.

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