Attenuated total reflection (ATR) is a method that allows the direct measurement of samples for FTIR. ATR method involves pressing the sample against a high-refractive-index prism and measuring the infrared spectrum using infrared light that is totally internally reflected in the prism. A diamond, zinc selenide (ZnSe) or germanium (Ge) prism is used in the ATR accessory. Most ATR accessories use a single bounce design, where the IR radiation interacts with the sample only once. Horizontal ATRs (HATRs) would interact with the sample up to 45 times increasing the signal, but use a larger amount of sample.
