Near-infrared spectroscopy transmittance measurements

A critical study has been carried out in order to evaluate the capabilities of Near Infrared spectroscopy for the analysis of commercial pesticide formulations using transmittance measurements. In this sense, it has been evaluated the determination of active ingredients in agrochemical formulations after extraction with an appropriate solvent. 

As several researchers have shown empirically, the use of —log(reflectance) can provide, analogous to a transmittance measurement, a linear relationship between the transformed reflectance and concentration, if the matrix is not strongly absorbing as can be found for many samples studied by near-infrared spectroscopy. This issue is presented in detail below. A different approach based on a physical model was considered for UV/VIS measurements and later also applied within the mid-infrared. A theory was derived by Kubelka and Munk for a simple, onedimensional, two-flux model, although it must be noted that Arthur Schuster (1905) had already come up with a reflectance function for isotropic scattering. A detailed description of theoretical and practical aspects was given by Korttim. The optical absorption... 

K. H. Norris and J. T. Kuenstner, Rapid Measurement of Analytes in Whole Blood with NIR Transmittance, in Leaping Ahead with Near Infrared Spectroscopy, ed. G. D. Batten, P. C. Flinn, L. A. Welsh, and A. B. Blakeney, NIR Spectroscopy Group, RACI, Australia, 1995, p. 431. 

B. Barabas. Comparison of measurability of two produces of high protein content. In Near Infrared diffuse reflectance/transmittance spectroscopy. Proceedings of the International NIR/NFF conference, Budapest, Hungary, May 12-16,1986. J. Hollo, et al co-eds. Akademiai Kiado, Budapest. 1987, p. 169-176. 

Y. A. Woo, Y. Terazawa, J. Y. Chen, C. lyo, F. Terada, S. Kawano. Development of a new measurement unit (MilkSpec-1) for rapid determination of fat, lactose, and protein in raw milk using near-infrared transmittance spectroscopy. Appl Spectrosc 56(5) 599-604,2002. C. Cimander, M. Carlsson, C. F. Mandenius. Sensor fusion for on-line monitoring of yoghurt fermentation. / Sioiec 99(3) 237-248, 2002. 

This technique is the most widely utilized variant of surface vibrational spectroscopy and is accomplished by simply measuring the transmittance of infrared radiation passing through the sample. A penetration of ca. 10 monolayers is necessary in order to achieve a satisfactory signal/noise ratio. For in-situ experiments zeolites are applied as pressed disks with a thickness of about 5-8 mg/cm. Due to the strong framework vibrations there is a nearly complete... 

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