Infrared spectroscopy is a technique which measures the infrared absorbances of various materials in gas, liquid, or solid phases using suitable sampling techniques. The infrared spectrum is qualitatively useful in determining the identity of a compound, as all materials have different infrared signatures. The infrared spectrum is also quantitatively useful as the strength of the infrared absorbances vary with concentration. Gas phase measurements using infrared spectroscopy are especially powerful as sample concentrations can be analyzed over 12 orders of magnitude, from parts-per-billion levels up to pure materials where trace impurities are of interest. The technology of infrared gas analysis is very mature and well-established in both industrial and research applications.