ATR FTIR

ATTENUATED TOTAL REFLECTION FTIR (ATR-FTIR)

Attenuated-total-reflectance (ATR) is a variant signal-sampling mode to conventional reflectance measurement that allows direct characterization of solids and liquids with minimal sample preparation and reduced post-measurement data processing. It is commonly performed alongside Fourier-transformed Infrared Spectroscopy (FTIR), which allows for chemical qualification of the sample from raw optical spectra.

For ATR-FTIR, a specialized accessory is incorporated in an FTIR system with an internal crystal that promotes multiple internal reflections of the incident IR beam. The crystal is oriented to be in direct contact with the sample surface, allowing the sample to absorb photons of characteristic energies, based on its chemical composition. When photons are absorbed, the reflected light wave will have attenuated intensity. A spectrometer parses the extent of this attenuation over the entirety of the sampled Infrared (IR) domain.

Peaks and unique conformations of the resulting ATR spectrum are then interpreted to yield chemical information about the functional groups and elements present in the sample.

Measurements from ATR-FTIR

  • Molecular composition (solid / liquid / gas)
  • Identification of functional groups

USES & LIMITATIONS FOR ATR-FTIR

  • What it is great for:
    • Identifying organic contamination
    • Identifying top-most thin film layer in a stack
    • Measuring thin films (typically 100 nm and up)
    • Works for solid, liquid, and powder samples
  • Limitations:
    • Many inorganic species don’t exhibit an FTIR spectrum
    • Requires the use of an appropriate reference library to ID chemicals
    • Some materials are not well-suited for FTIR: e.g. some metals (too reflective) and some glasses (too transmissive)

EXAMPLE OUTPUTS OF ATR-FTIR

ATR-FTIR spectrum

ATR-FTIR reference spectra: comparison of 2 variations of a synthesized thermoplastic polyurethane (S-TPU) generated for use in 3D printed biomedical devices.

From MDPI Open Access: https://doi.org/10.3390/ma12060887

INSTRUMENTS WE USE FOR ATR-FTIR

Thermo ftir 6700

Thermo Scientific™ Nicolet 6700 with
Smart iTR™ Attenuated Total Reflectance (ATR) Sampling Accessory

The Smart iTR ATR Sampling accessory eliminates sample preparation while retaining exceptional throughput with ultra-high-performance. Primarily designed for use with a single bounce diamond crystal, the Smart iTR Accessory also offers other options for full configurability up to multiple internal reflections. It provides exceptional sensitivity and IR throughput.