NIR analysis

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

T. Naes, T. Isaksson and B. Kowalski, Locally weighted regression in NIR analysis. Anal. Chem., 2 (1990) 664-673. 

The recommendations all have difficulties. In the first place, there is a specification that a minimum of five concentrations are to be used. However, reflecting the background of the guidelines in a world of univariate analyses, the different concentrations are to be created using dilution techniques. This method of creating samples is generally unsuitable for spectroscopic (especially NIR) analysis. 

Because NIR was initially used for food and agriculture products, it has evolved as a technique for complex matrices. Many types of hardware have become available for NIR work interference filters, gratings, interferometers, diode arrays, and acousto-optic tunable filters. And, as it was originally developed for complex mixtures, chemometrics has been an integral part of any NIR analysis for the last few decades. NIR practitioners are quite comfortable with multivariate equations and development of equations for complex matrices. 

A further example of process quality monitoring and reactor batch profiling using NIRS comes with oleo-chemical and biodiesel production. An established use of FT-NIR analysis (AOCS Method Cd le 01) is the determination of the key vegetable oil processing parameters - iodine value (IV) and percentage trans fat content (%Trans) (Figure 5.38). 

P. Dallin, NIR analysis in polymer reactions. Process Control and Quality, 9, 167-172 (1997). 

Tablets account for more than 80% of all pharmaceutical formulations therefore, the development and implementation of NIR methods for determining APIs in intact tablets is of a high interest with a view to assuring content uniformity and quality in the end product. Blanco et al developed an innovative strategy to prepare calibration samples for NIR analysis by using laboratory-made samples obtained by mixing the API and excipients in appropriate proportions and compacting the mixture at a pressure similar to that used industrially. This way of matching laboratory and production samples affords more simple and robust NIR methods which require the use of neither HPLC nor UV-vis spectroscopy as reference rather, reference values are obtained by weighing during preparation of the samples. The PLS calibration models thus constructed exhibited a good predictive ability with various production batches.

The history of NIR dates back to the studies by Herschel in 1800. The modern NIR analysis was developed in 1950 by the works of a group at USDA (U.S. Department of Agriculture), headed by Karl Norris (101). 

T. Nffis and H. Martens, Principal component regression in NIR analysis viewpoints, background details and selection of components, J. Chemom., 2(2), 1988, 155-167. 

Bruce, S. H. Proceedings of the First International Near Infrared Spectroscopy Conference, University of East Anglia, Norwich, U.K. (1987). Process NIR analysis. 

While there will be much more extensive discussions in later chapters on the topic of analyzer calibration, I will try to give you a quick snapshot here on how NIR analysis is done. The first step is to have a valid sample set, normally 30-50 samples covering the range of interest. The spectra are collected and a correlation is built between the wavelengths and their corresponding absorbencies and the reference analysis of these samples. The chemometric tools used in developing calibrations are discussed in Chapter 8. This is just the first step in developing a calibration but many people make the mistake of... 

Dallin, P., NIR Analysis in Polymer Reactions Process Contr. Qual. 1997, 9, 167-172. 

Near infra red reflectance spectroscopy (NIRS) is becoming increasingly used for the analysis of nutrients in feedstuffs. It is very rapid and cost-effective and may eventually replace the slower chemical methods of analysis used currently in the feed-manufacturing industry. NIRS may also be used for amino acid analysis. Another method now being adopted widely in feed manufacture is to use predichon equations based on chemical or NIRS analysis to predict amino acid contents of some feedstuffs. The NRC (1994) published equations for the predichon of lysine, tryptophan, threonine,... 

FIGURE 5.18 PCR (o), PLS ( ), and simplex () harmonious plots for NIR analysis of moisture in soy samples. The PCR and PLS 1 factor models are in the lower right comer, and the respective models are 8 and 7 factors in the upper left comer. The simplex models converged to RR and GRR models. The RMSEC values are with n — 1 degrees of freedom. 

Hammond SV (1992) NIR Analysis of Antibiotic Fermentations. In Murray I, Cowe IA (eds) Making Light Work Advances in Near-Infrared Spectroscopy. VCH Publishers,... 

NIR analysis is rapid, requiring less than one minute to analyze a single sample. Also, NIR analyses do not require the use and ultimate disposal of organic solvents, thereby reducing environmental waste. Advances in instrumentation, fiber optics, and software offer many options. Portable NIRS units are not uncommon. 

Borer and coworkers " published a useful evaluation of sources of variability encountered in the NIR analysis of drug products. Analysts involved in NIRS method development should consider this report. Parameters included in the study included. 

Shimoyama and coworkers " reported a NIR analysis of photodegradation of poly(methyl methacrylate) using an in situ fiber optic device. This type of technology from a related discipline is notable as a potential application for pharmaceutical systems. 

Although NIR spectra are not as information-rich or specific as FTIR spectra, the technique has experienced rapid growth. The increasing popularity of NIR absorption is driven mainly by sampling advantages, particularly the ability to obtain spectra noninvasively or with fiber optics. Since sample preparation is often not required, NIR analysis can be fast, inexpensive, and nondestructive. 

In two papers, Ritchie et al. [29,30] described an approach for performing qualitative NIR analysis of clinical samples with a concern for cGMPs (current good manufacturing practices). Since clinical lots are often ad hoc formulations, it is difficult to generate a discriminant equation prior to the actual clinical trial. Ritchie developed a procedure whereby equa-... 

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