Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR)

Attenuated-total-reflectance (ATR) is a sampling mode which enhances the Fourier Transformed Infrared Spectroscopy (FTIR) signal obtained from sample surfaces, increasing sensitivity and allowing efficient measurements with minimal sample preparation. Like standard FTIR measurements, ATR-FTIR is used for chemical qualification of a sample from raw optical spectra and is often used to determine organic composition.

Strengths

• Provides fingerprint identification of functional groups and compounds
• Extensive reference libraries and standardized quality testing procedures are available to aid data interpretation
• Capable of analyzing solid, liquid or powder samples

Limitations

• Most inorganic materials do not exhibit FTIR spectrum
  (carbonates, nitrates, silicates, sulfates DO exhibit FTIR spectra)
• Samples must not be too transmissive (some glasses) or too reflective (some metals)

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Example Outputs Instruments Used How ATR-FTIR Works

• Organic solid, liquid, powder, or aqueous samples work best
• Thin film minimum thickness: 100 nm

For ATR-FTIR, a specialized accessory is incorporated into an FTIR system. This accessory includes 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 it to absorb photons of characteristic energies based on its chemical composition. When incoming beams lose photons through absorption in the sample, the reflected light wave will have an 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.