Optimization of Data Recorded by Internal Reflectance Spectroscopy
Samples examined by Internal Reflection Spectroscopy (IRS) generally require minimal, or no, sample preparation. In Attenuated Total Reflection (ATR), a type of IRS, the sample is placed in contact against a special crystal, termed an internal reflectance element (IRE). The use of ATR in spectrometry is based upon the fact that although complete internal reflection occurs at the sample-crystal interface, as long as the angle of incidence is less than the critical angle, radiation does in fact penetrate a short distance into the sample. No universal material exists for IRS. Many of the IRS solid sampling accessories have cushioning pads (polytetrafluoroethylene, neoprene, etc.) on the faces of the plates used to apply pressure to the sample. It is apparent that the best IRS results will be obtained provided the analyst has access to several Internal Reflection Attachments possessing different geometries, as well as IREs having different refractive indices, so that the conditions used for each sample examination can be optimized.