Near-infrared spectroscopy reference analytical method

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... 

Despite the fact that near infrared spectroscopy (NIR) has been used industrially for decades [36], there has been hesitance to accept and trust new process analytical measurement technologies as equivalent or superior to traditional methods. For example, when a discrepancy between online NIR and laboratory analyses is observed, it is rare that the destructive reference methods are ever targeted as the source of error, despite the fact that NIR is often the more precise method. The hesitance to trust more advanced, multivariate tools (which are perhaps less directly understood) has certainly been a detriment to progress in deploying PAT. 

Near-infrared (NIR) absorption spectroscopy is another technique of importance to the context of the development of analytical Raman spectroscopy. The method is generally referred to as NIR, despite the unfortunate confusion with NIR-Raman. NIR absorption is based on overtone and combination bands of mid-IR transitions, as shown in Figure 1.1. Such transitions are quantum mechanically forbidden and significantly weaker than mid-IR fundamentals. However, the higher energy photons involved in NIR absorption are transmitted by fiber optics and common optical materials, and the method has... 

Figure 1 presents what may be referred to as the near-infrared method validation pyramid. Ritchie [11] presented this idea at the Ninth International Diffuse Reflectance Conference (Chambersburg) in 1998. Since then, he has presented it at the Spectroscopy in Process and Quality Control Conference (SPQ) in 1999, the Eastern Analytical Symposium (EAS) in 1999, and the Pittsburgh Conference and Exposition on Analytical Chemistry and Applied Spectroscopy (PittCon) in 2000. 

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