Near-infrared spectroscop measurement methods

Fourier transform near-infrared spectroscopy, using the C=CH band at 61S2cm for methacrylates, enabled the conversion to be followed in a single sample throughout the polymerization to high conversion. Parallel experiments were performed for near-infrared spectroscopic determination of monomer concentrations and for ESR measurements of radical concentrations. A further advantage of the near-IR method is its applicability to insoluble crosslinked systems. 

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. 

The concept of the PCSA method is general and this method should be applicable to many types of multivariate calibration techniques. As near-infrared and other spectroscopic methods are developed further for noninvasive in vivo clinical measurements, it is critical to understand the chemical basis of measurement selectivity. Unfortunately, calibration models generated from multivariate statistics are typically accepted without further investigation. Application of the PCSA method can help to establish the chemical or spectroscopic basis of predicted concentrations. 

Spectroscopic methods are also commonly used for the analysis of surfactants. Among these methods ultraviolet/visible spectrophotometry and infrared/near-infrared spectroscopy are used for the measurement of surfactant concentration, while such techniques as nuclear magnetic resonance (NMR) and mass-spectroscopy (MS) are extensively used for... 

Fourier transform mid-infrared (FTIR), near-infrared (FTNIR), and Raman (FT-Raman) spectroscopy were used for discrimination among 10 different edible oils and fats, and for comparing the performance of these spectroscopic methods in edible oil/fat studies. The FTIR apparatus was equipped with a deuterated triglycine sulfate (DTGS) detector, while the same spectrometer was also used for FT-NIR and FT-Raman measurements with additional accessories and detectors. The spectral features of edible oils and fats were studied and the unsaturation bond (C=C) in IR and Raman spectra was identified and used for the discriminant analysis. Linear discriminant analysis (LDA) and canonical variate analysis (CVA) were used for the disaimination and classification of different edible oils and fats based on spectral data. FTIR spectroscopy measurements in conjunction with CVA yielded about 98% classification accuracy of oils and fats followed by FT-Raman (94%) and FTNIR (93%) methods however, the number of factors was much higher for the FT-Raman and FT-NIR methods. 

Spectroscopic techniques can be used to detect drug crystallinity, drug-polymer compatibility, or to measure the concentration of the drug present in the HME formulations. Commonly used spectroscopic methods are UV-visible, infrared, Raman, and near-infrared. FTIR is also used to detect the phase separation within the HME samples. ... 

Nonpulsatile optical spectroscopy has been used for more than half a century for noninvasive medical assessment, such as in the use of multiwavelength tissue analysis for oximetry and skin reflectance measurement for bilirubin assessment in jaundiced neonates. These early applications have found some limited use, but with modest impact. Recent investigations into new nonpulsatile spectroscopy methods for assessment of deep-tissue oxygenation (e.g., cerebral oxygen monitoring), for evaluation of respiratory status at the cellular level, and for the detection of other critical analytes, such as glucose, may yet prove more fruitful. The former applications have led to spectroscopic studies of cytochromes in tissues, and the latter has led to considerable work into new approaches in near-infrared analysis of intact tissues. 

Therefore, during the past 30 years, numerous vibrational spectroscopic methods (near infrared, NIR infrared, IR and Raman spectroscopy) have been introduced as very efficient alternatives, which are widely used today to determine fats, proteins, and carbohydrates and also numerous secondary plant substances occurring in agricultural products. For authentication purposes, the mentioned spectroscopic techniques can provide the valuable data in a few minutes, allowing the discrimination of different agrofood samples. Also new developments of IR and Raman microscopes have considerably extended the field of application. These sophisticated techniques allow to perform point-by-point measurements (mapping) or to acquire simultaneously spectra (imaging) from a small sample area. 

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