ATRläge

ATRläge, short for Attenuated Total Reflectance mode, is a technique used in infrared spectroscopy to obtain spectra of samples with minimal preparation. It relies on the ATR principle to measure how a sample absorbs infrared light close to a crystal surface rather than through transmission.

In ATR mode, infrared light is directed into a crystal with a high refractive index. The light reflects internally at the crystal–sample interface, and an evanescent wave extends a short distance into the sample. If the sample absorbs at certain wavelengths, the reflected light is reduced at those wavelengths, producing an infrared spectrum that corresponds to the sample’s near-surface composition. The depth of penetration is typically on the order of a few hundred nanometers to a few micrometers and depends on the wavelength, the crystal and sample refractive indices, angle of incidence, and polarization.

Typical ATR setups use crystals made from diamond, zinc selenide (ZnSe), germanium, or other materials, mounted in an FTIR spectrometer with an accessory to press the sample against the crystal. The method works for solids, powders, liquids, and pastes, and requires only limited or no sample preparation.

Advantages include minimal sample prep, compatibility with a wide range of materials, and the ability to analyze rough or opaque surfaces. Limitations include quantitative interpretation challenges due to variable penetration depth and contact quality; spectra may differ in shape from transmission spectra, necessitating corrections or calibration for accurate comparisons.

ATRläge is widely used in polymers, pharmaceuticals, coatings, foods, and geological analyses for rapid identification and routine quality control.