AOTF-NIR\u5149\u8c31\u4eea<\/a>\u53ca\u5176\u8010\u7528\u575a\u56fa\uff0c\u5bf9\u673a\u68b0\u632f\u52a8\u548c\u73af\u5883\u5149\u53d8\u5316\u4e0d\u654f\u611f\uff0c\u662f\u751f\u4ea7\u7ebf\u5b9e\u65bd\u7684\u7406\u60f3\u5de5\u5177\u3002\u6b64\u5916\uff0c\u5b83\u4eec\u50cf\u5168\u5149\u675f\u5149\u8c31\u4eea\u4e00\u6837\u5de5\u4f5c\uff0c\u56e0\u6b64\u975e\u5e38\u9002\u5408\u5728\u7ebf\u76d1\u6d4b\uff0c\u65e0\u9700\u6267\u884c\u9891\u7e41\u7684\u80cc\u666f\u6821\u6b63\u548c\u6821\u51c6\u3002<\/p>\n <\/p>\n The principle of the Acousto-Optic Tunable Filter<\/a> (AOTF<\/a>) is based upon the acoustic diffraction of light in an an-isotropic medium.\u00a0 The device consists of a piezo-electric transducer bonded to a birefringent crystal.\u00a0 When the transducer is excited by an applied RF signal, acoustic waves are generated in the crystal.\u00a0 The propagating acoustic wave produces a periodic modulation of the refractive index.\u00a0 This provides a moving phase grating that under proper conditions will diffract portions of an incident light beam.\u00a0 For a fixed acoustic frequency, a narrow band of optical frequencies satisfies the phase matching conditions and be cumulatively diffracted.\u00a0 As the RF frequency is changed, the center of the optical band-pass is changed accordingly so that the phase matching condition is maintained.<\/p>\n The near infrared region of the spectrum extends from 800nm to 2500nm.\u00a0 The absorption bands which are most prominent in this region are due to overtones and<\/p>\n combinations of the fundamental vibrations active in the mid infrared region.\u00a0 The energy transitions are between the ground state and the second or third excited vibrational states.\u00a0 Because higher energy transitions are successively less likely to occur, each overtone is successively weaker in intensity.\u00a0 Since the energy required to reach the second or third excited state is approximately twice or three times that needed for a first order transition and the wavelength of absorption is inversely proportional to the energy, the absorption bands occur at about one-half and one-third the wavelength of the fundamental.\u00a0 In addition to the simple overtones, combination bands also occur.\u00a0 These usually involve a stretch plus one or more bending of rocking modes.\u00a0 Many different combinations are possible and therefore the NIR<\/a> region is complex, with many band assignments unresolved.<\/p>\n Near Infrared Spectroscopy is currently being used as a quantitative tool which relies on chemometrics to develop calibrations relating a reference analysis of the constituent to that of the NIR optical spectrum.\u00a0 The mathematical treatment of NIR data includes Multi Linear Regression (MLR), Principle Component Analysis (PCA), Principle Component Regression<\/p>\n (PCR), Partial Least Squares (PLS) and discriminant analysis.\u00a0 All of these algorithms can be used singularly or in combination to yield the resultant goal of quantitative prediction and qualitative description of the constituents of interest.<\/p>\n 2.\u00a0 Methodology<\/p>\n The spectrometer used was a Brimrose AOTF-NIR Luminar<\/a> spectrometer connected to 600-micron single fiber optic cables.\u00a0 The fibers were then connected to a Brimrose custom designed cuvette holder, which was able to secure the cuvette.\u00a0 The effective pathlength of the cuvette was 2mm.\u00a0 Samples of menthol and ethanol were mixed in different proportions.\u00a0 Each sample was scanned 75 times from 900nm to 1700nm and the scans were averaged into one spectrum.\u00a0 The region between 900nm and 1700nm is the most ideal range in which to work because the first overtone of alcohols occurs in the 1405nm to 1425nm range and the second overtones of CH3<\/sub> stretching bonds occur in the 1192nm to 1200nm range. The spectra were collected in transmission mode and processed into absorbance and first derivative.<\/p>\n The first derivative data shown above were used for performing the calibration and validation calculations using the chemometrics software package Unscrambler\u00e4 from Camo.\u00a0 A PLS1 full cross validation method was used for modeling. The model for the first derivative spectra clearly showed better results than the model for the absorbance spectra. The correlation for both the calibration and validation set for ethanol and menthol is 0.99 and the SEP is 0.648 and 3.805 respectively.<\/p>\n \u00a0<\/strong><\/p>\n Nineteen samples were used as a test set to validate the model. The standard deviation of differences between measured and predicted (SEP) for the 19 test set samples of ethanol and menthol was 0.44 and 2.67 respectively.<\/p>\n <\/p>\n \u5149\u8c31\u6cd5\u6d4b\u91cf\u55b7\u96fe\u5316\u5b66\u6eb6\u6db2\u4e2d\u4e59\u9187\u548c\u8584\u8377\u9187\u7684\u767e\u5206\u6bd4\u542b\u91cf \u603b\u7ed3 \u901a\u8fc7\u5bf9\u4e59\u9187\u548c\u8584\u8377\u9187\u6eb6\u6db2\u4e0d\u540c\u6bd4\u4f8b\u6837\u54c1\u7684\u7814\u7a76\u8868\u660e\uff0c\u5728\u55b7\u96fe\u6eb6\u6db2\u4e2d\u5b9e\u65f6\u6d4b\u5b9a\u4e59\u9187\u548c\u8584\u8377\u9187\u767e\u5206\u6bd4\u542b\u91cf\u662f\u975e\u5e38\u53ef\u884c\u7684\u3002\u53ef\u4ee5\u901a\u8fc7\u5b89\u88c5\u5e26\u5355\u6839\u5149\u7ea4 <\/p>\n","protected":false},"author":19,"featured_media":210,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[19],"tags":[33,34,43,48,47,53,61,55,49,141,142,36,35,63,41,59,50,51,57,60,45,52,56,58,37,39,44],"_links":{"self":[{"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/posts\/238"}],"collection":[{"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/users\/19"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/comments?post=238"}],"version-history":[{"count":0,"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/posts\/238\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/media\/210"}],"wp:attachment":[{"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/media?parent=238"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/categories?post=238"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bihec.com\/brimrose\/wp-json\/wp\/v2\/tags?post=238"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\n
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