Sample preparation, near reflectance analysis

Mark, H. "Use of Mahalanobis Distances to Evaluate Sample Preparation Methods for Near-Infrared Reflectance Analysis", Anal. Chem. 1987 (59) 790-795. 

Near infrared spectroscopy (NIRS), a technique based on absorption and reflectance of monochromatographic radiation by samples over a wavelength range of 400-2500 run, has been successfully applied for food composition analysis, for food quality assessment, and in pharmaceutical production control. NIRS can be used to differentiate various samples via pattern recognitions. The technique is fast and nondestructive method that does not require sample preparation and is very simple to use compared too many other analytical methods such as HPLC. The drawback of NIRS, however, is that the instrument has to be calibrated using a set of samples typically 20-50 with known analyte concentrations obtained by suitable reference methods such as FIPLC in order to be used for quantitative analyses. Simultaneous quantification of the... 

FTIR spectra in the near-IR region consist entirely of overtones and combinations of primary bands within the mid-IR region. For macromolecules or complex mixtures, the excessive overlapping of bands produces a diffuse absorption continuum with few characteristic features, making unequivocal band assignment practically imposssible. Thus, this spectral range has a limited use in qualitative analysis. Even so, a major asset of near-IR analysis is the ease with which reproducible spectra can be obtained by reflectance and transreflectance (a combination of transmission and reflectance) techniques in every state of aggregation without complicated sample preparation. 

Sampling, sample handling, and storage and sample preparation methods are extensively covered, and modern methods such as accelerated solvent extraction, solid-phase microextraction (SPME), QuEChERS, and microwave techniques are included. Instrumentation, the analysis of liquids and solids, and applications of NMR are discussed in detail. A section on hyphenated NMR techniques is included, along with an expanded section on MRI and advanced imaging. The IR instrumentation section is focused on FTIR instrumentation. Absorption, emission, and reflectance spectroscopy are discussed, as is ETIR microscopy. ATR has been expanded. Near-IR instrumentation and applications are presented, and the topic of chemometrics is introduced. Coverage of Raman spectroscopy includes resonance Raman, surface-enhanced Raman, and Raman microscopy. 

Near-infrared reflectance analysis is a useful technique for characterizing textile raw materials, fiber, yarns, and fabrics. It is a nondestructive quantitative analysis that is simple to use and allows rapid testing of the sample. Its ability to measure multiple components of the sample simultaneously and eliminate extensive sample preparation are major advantages of NIRA in the characterization of textile materials. Many innovative mathematical treatments, for example, discriminant analysis and spectral reconstruction, have been developed by instrument manufactures and software companies. These instruments not only aid in the quantitative analysis of the data but also allow morphological investigations of fibers and yarns and rapid, qualitative identification of specific sample sets. 

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