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Data treatment in near infrared spectroscopy

1998; EDP Sciences; Volume: 26; Issue: 4 Linguagem: Inglês

10.1051/analusis

1286-482X

Pierre Chaminade, A. Baillet, D. Ferrier,

Spectroscopy and Chemometric Analyses

The near infra red (NIR) takes place between midd l e infrared and visible region of the spectrum.As quartz is tra n s p a rent in near infra red regi o n , t ra n s m i t t a n c e m e a s u rements of liquids can be done using standard s cuvettes and, reflectance measurements of powders can be realised using fiber optics.NIR spectro s c o py is thus a method that re q u i re few or no sample prep a rat i o n .Absorption bands observed in NIR spectra are due to overtones of, mainly, hydrogenic stretching vibrations or combination involving stretching and bending modes of vibration.Those bands are thus broader than in middle infrared and spectra are considerably more complex.Due to this comp l ex i t y, NIR spectro s c o py has soon taken adva n t age of sophisticated calibration techniques and is now using state of the art data treatment.This article will illustrate, first the spectral transformation and then the two current uses of NIR spectroscopy : qualitative discriminant analysis and quantitative applications. ExperimentalQ u a l i t at ive discriminant ap p l i c at i o n : m a n n i t o l , s o r b i t o l P100T, sorbitol P60, sorbitol P20-60, hydroxyethylcellulose, hydroxypropylcellulose (Roquette, Lestrèmes, France).Quantitative application: Paracetamol (Sigma, St. Quentin Fallavier, France) with variable amounts of hydroxypropylcellulose (Roquette) and lactose monohydrate (Sigma).The measurement where done with a BUHLER-NIRVIS s p e c t rometer and a 2 meters optical fi b re.Calculat i o n s wh e re done using NIRCAL 2.0 softwa re (BU H L E R -ANATEC, Uzwil, Switzerland). Spectrum transformationFour different goals can be reached by spectra transformation:Since the last ten years, the use of near-infrared spectroscopy is increasing due to the improvement of instrumentation and software.The calculation capacity of today computers allows a promising future for this technique.According to the complexity of structural attribution of absorption bands, only a chemometric approach is able to solve qualitative and quantitative applications.Depending on spectrophotometers and analytical context, the signal treatment and the calculation strategy may vary.For an identification task, cluster analysis is built on spectral data from only a few wavelengths using disperse spectrophotometer when principal component analysis is applied on overall spectral range with interferometer based apparatus.The main quantitative calculation modes i.e.MLR, PCR and PLS are discussed.