Near-ir and Mid-ir Process Analysis — a Critical Comparison

Over the past several years, both near infrared (NIR) and mid infrared (MIR) spectroscopy have steadily gained acceptance as powerful methods for at-line and on-line analysis. These methods share the advantages of high speed, robust calibration, and low service requirements compared to more established process analytical techniques such as gas chromatography. However, despite their many similarities, NIR and MIR are often viewed as distinct technologies, competing for the same market segments. This paper reviews the fundamentals of infrared analysis from the spectroscopic viewpoint, stressing both the common and disparate features of NIR and MIR and highlighting the fact that — rather than being two distinct technologies — NIR and MIR represent the endpoints of a continuum of analytical possibilities. Particular emphasis is placed on the spectral characteristics of typical organic materials and on the effects of these on the choice of spectral region and sample interfacing method for use in a given analysis.