Water NIRA determination

Extensive use has been made of NIRA in agriculture where it has been used to determine the protein, fibre, water and triglyceride contents of feedstuffs and the quality of crops. By training the computer to recognise the near-infrared (NIR) spectra of the major components making up a crop, the individual components can be monitored in the crop itself. The components that can be measured by NIRA often cannot be measured by the usual spectroscopic methods. The fundamental work done in the quality control of agricultural products can be readily extended to the quality control of pharmaceutical formulations. 

Near-Infrared Spectroscopy. Near-infrared (NIR) spectroscopy is a technique that has been around for some time but, like NMR spectroscopy, has only recently been improved and developed for on-line applications. Near-infrared analysis (NIRA) is a nondestructive technique that is versatile in the sense that it allows many constituents to be analyzed simultaneously 112, 113). The NIR spectrum of a sample depends upon the anharmonic bond vibrations of the constituent molecules. This condition means that the temperature, moisture content, bonding changes, and concentrations of various components in the sample can be determined simultaneously. In addition, scattering by particles such as sand and clay in the sample also allows (in principle) the determination of particle size distributions by NIRA. Such analyses can be used to determine the size of droplets in oil-water emulsions. 

To determine the oil, water, and solids contents simultaneously, sophisticated statistical techniques must usually be applied, such as partial least-squares analysis (PLS) and multivariate analysis (MVA). This approach requires a great deal of preparation and analysis of standards for calibration. Near-infrared peaks can generally be quantified by using Beer s law consequently, NIRA is an excellent analytical tool. In addition, NIRA has a fast spectral acquisition time and can be adapted to fiber optics this adaptability allows the instrument to be placed in a control room somewhat isolated from the plant environment. 

A. Picarelli, M. Greco, F. Di Giovambattista, A. Ramazzotti, C. Cedrone, E. Coarzziari, and A. Torsoli. Quantitative determination of faecal fat, nitrogen and water by means of a spectrophotometric technique near infrared reflectance analysis (NIRA). Assessment of its accuracy and reproducibility compared with chemical methods. Clin. Chim. Acta 234 147 (1995). 

The color of refined wheat flour (AACC Method 14-30) or semolina is generally performed in an Agtion colorimeter operating in the green mode (546 nm). The sample (20 g) is mixed with 25 mL distilled water for 2 min in order to enhance color formation. Next, the slurry is read in the colorimeter that was previously calibrated with disc standards 0, 63, 85, and 100. Similar assays (AACC Methods 14-21 and 14-22) are also used to measure pasta and noodle color. The NIRA can be also calibrated to determine color. 

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