What Are Infrared Spectra Used For

We measure infrared spectra to answer questions about samples. One question we commonly try to answer is, What molecules are present in this sample , otherwise called unknown analysis. The peak positions in an infrared spectrum correlate with molecular structure, which is part of why infrared spectroscopy is useful. Over the last 100-plus years a great number of infrared spectra have been measured, and the peak positions of known molecules derived from these spectra can be used to identify the molecules in an unknown sample [1]. 

A third question an infrared spectrum can answer is, What are the concentrations of molecules in this sample To do this one must measure the spectra of samples of known concentration, and then use Beer s Law (Equation 1.6) to prepare a calibration line relating absorbance to concentration. Once the calibration has been generated and validated it can be used to determine the concentration of molecules in unknown samples. For more on quantitative analysis see Chapter 5 of this volumes or my book on quantitative spectroscopy [2], 

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