The Investigation of Calibration Performance Variation in Three Different Spectral Regions in Near-Infrared RangeThe Investigation of Calibration Performance Variation in Three Different Spectral Regions in Near-Infrared RangeThe Investigation of Calibration Performance Variation in Three Different Spectral Regions in Near-Infrared RangeThe Investigation of Calibration Performance Variation in Three Different Spectral Regions in Near-Infrared RangeThe Investigation of Calibration Performance Variation in Three Different Spectral Regions in Near-Infrared Range

Abstract

When NIR spectroscopy is used for quantitative calibration of organic system, three spectral regions (combination, first overtone and second overtone regions) are available. These three regions correspond to 9090-6500, 6500-5000 and 5000-4000 cm-1 range. However, only one region should be selected when an actual quantitative measurement is performed since all three ranges can not be collected using one fixed pathlength. The major goal of this study was to investigate quantitative calibration performances of each region when signal-to-noise ratio was maintained at constant. Simultaneously, the relationship between spectral feature and calibration performance in each region was studied. For this purpose, n-hexane and toluene were selected as an analyte, and n-heptane was used as solvent. The signal-to-noise ratio of was controlled at constant level by changing the scan numbers. In all cases, PLS (Partial Least Squares) regression was used as calibration. For n-hexane (similar spectral feature over solvent) case, the calibration result was degraded when second overtone region (9090-6500 cm-1, further from Mid-region) since spectral features were broaden and overlapped in this region. However, for toluene, calibration results were almost similar over three different regions due to unique spectral features over solvent. Even though the spectral bands were broaden in the second overtone region, it was enough to observe the feature of toluene, but no significant feature of n-hexane in the same region. When NIR spectroscopy is employed, the spectral feature of analye and spectral range for calibration are simultaneously considered for optimal analysis.