Attenuated total reflectance (ATR) spectroscopy is a technique used in analytical chemistry to obtain IR spectra of samples. It is particularly useful for analyzing solid and liquid samples without the need for extensive sample preparation. ATR spectroscopy works based on the principle of internal reflection of infrared light.
The key features of attenuated total reflectance spectroscopy include:
Internal reflection: A beam of infrared light is directed into a crystal, typically made of a material like diamond, germanium, or zinc selenide. This crystal has a high refractive index compared to the sample being analyzed.
Total internal reflection: When the infrared light strikes the crystal/sample interface at an angle greater than the critical angle, it undergoes total internal reflection within the crystal.
Evanescent wave: During total internal reflection, an evanescent wave is formed at the crystal/sample interface. This wave penetrates a short distance into the sample.
Sample interaction: The evanescent wave interacts with the sample, leading to absorption of specific wavelengths of infrared light. The extent of absorption depends on the sample's composition and the concentration of its chemical components.
Spectral analysis: The transmitted light through the crystal is analyzed to produce an ATR spectrum, which represents the absorption of infrared light by the sample. This spectrum provides information about the functional groups and chemical composition of the sample.
Attenuated total reflectance spectroscopy has several advantages:
Sample versatility: ATR spectroscopy is suitable for a wide range of sample types, including solids, liquids, gels, and pastes, without the need for extensive sample preparation.
Real-time analysis: The technique allows for real-time analysis, making it useful for monitoring reactions or processes.
High sensitivity: ATR spectroscopy is sensitive to surface layers of samples, making it effective for thin films or coatings.
This technique is commonly employed in fields such as chemistry, biology, pharmaceuticals, and material science for the qualitative and quantitative analysis of a variety of samples. It provides valuable information about the molecular composition and structure of materials.