Effects of temperature on near-infrared spectroscopic measurement of glucose
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The noninvasive monitoring of sugars and, in particular, glucose using near-infrared (NIR) spectroscopy would be useful for a number of applications including regulating the nutrients in cell culture medium, monitoring on-line processes in the food industry, and in vivo monitoring for control of glucose in Diabetic patients. The focus of this research was the investigation of the temperature effects across a 10.6 to 40.4 C range on Fourier filtered and unfiltered single-beam as well as absorbance glucose and water NIR spectra (2.0-2.5 m). It is known that the positions of water absorption bands centered at 1.923 and 2.623 m depend heavily on temperature effects while the glucose bands ( 2.105, 2.237, and 2.326 m) are temperature insensitive across this range. The water absorption bands were shown to shift to lower wavelengths while the distance between these bands increased with increasing temperatures. Partial least squares (PLS) calibration models were constructed at five separate temperatures, 15.7, 20.5, 25.5, 35.6, and 40.4 C. When absorbance spectra were used with reference scans taken at the same temperature and PLS models were used, no significant difference in the standard error of prediction (SEP) was noted with temperature. Using PLS calibration with single-beam spectra at one temperature showed large SEP's at the other temperatures. The use of Fourier filtered single-beam spectra reduced the SEP but still showed an increase as large temperature differences were produced and the filtered single beam approach did not reduce the SEP to the level achieved with the absorbance spectra.