Near-Infrared Spectra of Gases
Near-infrared (NIR) spectroscopy has been used extensively in agriculture, pharmaceutical, and process control areas [1-8]. It is an ideal method for determining moisture and protein content of food products [1-3], composition and thickness of polymer films , and octane ratings of gasoline [6,8]. More and more practical uses of NIR are discovered each year. However, NIR applications to gases have been very limited. Mid-infrared (MIR) has been used to monitor the composition of environmental gases for many years [9,10]. The major difference between MIR and NIR of gases is in the sensitivity. Absorptivities in the MIR are 10-to 100-fold stronger than those in the NIR. There has also been some concern about the selectivity of NIR vs. MIR, since bands tend to be broader and there is more overlap in the NIR region.