SIGNIFICANCE OF TEMPERATURE CONTROL IN FT-NIR SPECTROMETERS

Recent applications of near-infrared (NIR) spectroscopy to process analysis based on principal component regression or other chemometric algorithms have shown that NIR spectrometers become unstable after extended use. In the present study, stability problems are reported to occur within a 24-hour period. The instability was found to be at a maximum when highly IR-absorbing materials were analyzed and was attributed to temperature fluctuations in both the cooling water to the source and the purge gas to the optical bench. The problem was alleviated by using a thermostated recirculator and liquid nitrogen boil-off. Ensuing discussions show the problem to be relevant to other instruments which perform Fourier transformations on interferograms.