In today's FTIR market, many instrument manufacturers provide software to perform searches of computer library spectra. With the increased speed of computers running FTIR instruments, you can have the result of a computer library search in literally seconds. However, as we rely more and more on computers in the laboratory we need to keep in mind the limitations and possible areas for error in these applications.

Computer library search programs calculate the difference between the sample spectrum and reference spectrum typically based on peak position and intensity. Different searching algorithms can stress one or the other. The result of a computer search is a Hit List with each hit having a hit quotient index (HQI) to indicate how close that particular spectrum matches the sample spectrum. In some programs the quotient which indicates an exact match would be 1 or 100, in others it is 0.