Near-Infrared Analysis (NIRA): A Technology for Quantitative and Qualitative Analysis

Abstract The near-infrared (NIR) region (defined by the ASTM Working Group on NIR as 180 to 2526 nm, October 1985) was the first nonvisible portion of the spectrum to be found, in 1800, by Herschel [1]. The vibrational absorptions in the near-infrared are overtone and combination frequencies of absorption bands that occur in the mid-infrared. These overtones and combinations cause overlapping absorption bands, which make it more difficult to visually identify chemical groupings of a molecule from their near-infrared spectra than from the "fingerprint" region of the mid-infrared spectrum. The overtone and combination bands are one to three orders of magnitude weaker than the fundamental bands. This provides singularly useful sampling advantages.