Optical-fiber measurements coupled with near-infrared analysis is used to predict the ethanol content of wine samples to within ±0.33 volume percent. Because telecommunications-grade optical fibers are used, the wavelength range is limited and the signal-to-noise ratio is an order of magnitude less than that for conventional near-infrared measurements. These features prompted the use of partial least-squares (PLS) as the calibration algorithm. PLS provides robust calibrations that are based upon the entire spectrum. The problem of extreme samples not being represented in the calibration model is discussed and illustrated. Also, the robustness of the PLS calibration is demonstrated. Spectral reconstruction is used to help assign the bands in the wavelength range used.
Because of methanol's relatively low cost and its utility as an octane booster, a need to monitor the concentration of methanol in gasolines has evolved. Near-infrared analysis can be used to monitor methanol in gasolines with the use of optical fiber. If stepwise multiple linear regression is used, methanol can be predicted to within 0.25 weight percent. The use of an optical fiber lowers personnel and instrument exposure to hazardous environments and minimizes the risk of explosion. It is pointed out, however, that care must be taken in the prediction of future specimens. The differences between enumerative and analytical calibrations are also discussed.
NIR analysis allowed the evaluation of the efficiency of a new drug film coating manufacturing process more quickly and inexpensively. Because the Near-Infrared method was non-invasive the tablets were available for further analysis unlike the chromatography method.
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