Advantages and Disadvantages of Reflectance Sampling

In reflectance sampling it takes extra mirrors to focus the light onto the sample and to collect the reflected light. These extra mirrors are contained in reflectance accessories that either mount on the base plate in the FTIR sample compartment or slide into the sample slide mount. These accessories must be custom built for the make and model of FTIR in which they are going to be used. A problem with reflectance accessories is that they are thousands of dollars more expensive than transmission accessories. There are several companies that make customized FTIR reflectance accessories, and they can be found via an Internet search. 

In transmission, the spectrum is of the bulk of the sample with little surface contribution. In reflectance, the light bounces off the surface of the sample so the surface contributes strongly to the overall spectrum. This surface sensitivity of reflectance techniques is good if you are interested in knowing the composition of the surface of a sample. However, if you are interested in the spectrum of the bulk of a sample, and the surface and the bulk have different chemical compositions, the reflectance spectrum of the sample will not give a complete picture of the composition of the sample. 

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