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Attenuated Total Reflectance (ATR)
Attenuated Total Reflectance (ATR)
Attenuated Total Reflectance InfraRed spectroscopy (ATR-IR) is an infrared spectroscopic method which requires no special sample preparation for analysis. A sample (solid or liquid) is placed onto the ATR crystal (usually diamond) and the beam passes through the crystal bouncing off the surface with absorbances occurring at the interface between the crystal and compound. The ease and speed of ATR-IR spectroscopy makes it a suitable technique for widespread use. However some functionalities are better analysed using alternative IR methods and gas-phase compounds are unsuitable for ATR-IR spectroscopy.
Compound being placed onto an ATR-IR Spectrometer
Method
Method
ATR spectrometers are designed for ease of use in recording liquid or solid compounds. An infrared beam is shone through a crystal which exhibits properties of total internal reflection. Evanescent waves result as the light passes through the crystal (for example a diamond or zinc selenide), and energy of these waves is absorbed by compounds in contact with the crystal at specific frequencies. Through recording a background measurement and subtracting this from the sample measurement results in a spectrum for the compound.
A close up of an ATR spectrometer with a solid compound being placed onto the crystal
For solid samples, a clamp is used to place pressure onto the sample to ensure good contact is made between the compound and the crystal to ensure good absorption of the evanescent beam. For liquids, these usually adhere to the crystal surface without any need for pressure to be applied to the sample.
Once a sample has been recorded, the sample needs to be removed from the crystal and spectrometer plate. Usually this is acheived by wiping the plate and crystal with a tissue containing a suitable solvent to remove the compound, but without causing damage to the instrument. Most commonly isopropyl alcohol (IPA) is used.
Checking data acquisition
Checking data acquisition
When recording a spectrum, it is important to check that data acquisition has been successful at the time of recording. A guide for checking spectra recorded via ATR, along with examples of common problems, can be found below.
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