NIRS, analytical method

Some analytical methods are highly mature (NAA, XRD, XRF, XAS), the theory is well assessed, and just instrumental and incremental improvements (more intense sources, better detectors) may be expected. However, in many other areas the sharply increasing power of analytical instrumentation (with regard to both hardware and software) and its transformation into tools for in-process control (such as NIRS, LR-NMR, etc.) are most appropriately considered as breakthroughs. 

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... 

The standard analytical methods for biodiesel methyl ester are time-consuming and often require multiple physical analyzes per sample. NIRS allows for the simple set up of calibrations for multiple important biodiesel qualities such as mono-, di- and triglycerides, residual methanol, glycerol and moisture as well as... 

Even if a rogue material is detected but is unidentifiable by its NIR spectrum alone, the location information derived from the imaging experiment can greatly assist in the rapid analysis of the snspect region by other analytical methods. 

In some manufacturing process analysis applications the analyte requires sample preparation (dilution, derivatization, etc.) to afford a suitable analytical method. Derivatization, emission enhancement, and other extrinsic fluorescent approaches described previously are examples of such methods. On-line methods, in particular those requiring chemical reaction, are often reserved for unique cases where other PAT techniques (e.g., UV-vis, NIR, etc.) are insufficient (e.g., very low concentrations) and real-time process control is imperative. That is, there are several complexities to address with these types of on-line solutions to realize a robust process analysis method such as post reaction cleanup, filtering of reaction byproducts, etc. Nevertheless, real-time sample preparation is achieved via an on-line sample conditioning system. These systems can also address harsh process stream conditions (flow, pressure, temperature, etc.) that are either not appropriate for the desired measurement accuracy or precision or the mechanical limitations of the inline insertion probe or flow cell. This section summarizes some of the common LIF monitoring applications across various sectors. 

The strict regulations of the pharmaceutical industry have a significant effect on the quality control of final products, demanding the use of reliable and fast analytical methods. The capacity that the technique has for the simultaneous determination of several APIs with no need of, or with minimum, sample preparation has considerably increased its application in pharmaceutical analytical control. The main limitation of NIR is the relatively low sensitivity that limits the determination of APIs in preparations when their concentration is less than 0.1%. Nevertheless, instrumental improvements allow the determination below this limit depending on the nature of the analyte and the matrix, with comparable errors to the ones obtained with other instrumental techniques. The reference list presents an ample variety of analytical methodologies, types of samples, nature of analyte and calibration models. A detailed treatment of each one is beyond the scope of... 

Organic and inorganic molecular species (except homonuclear molecules) absorb in the IR region. IR spectroscopy has the potential to determine the identity of an unusually large number of substances. Moreover, the uniqueness of a MIR spectrum confers a degree of specificity which is matched or exceeded by relatively few other analytical methods. This specificity has found particular applications for the development of quantitative IR absorption methods. However, these differ from quantitative UV/Vis techniques in their greater spectral complexity, narrower absorption bands, and the technical limitations of IR instruments. Quantitative determinations obtained from IR spectra are usually inferior in quality and robustness to those obtained with UV/Vis and NIR spectroscopy. In addition, univariate or linear cali-... 

The Instrumental Criteria Sub-committee of the Analytical Methods Committee has been active for many years in producing Guidelines for the Evaluation of Analytical Instrumentation. Since 1984, they have produced reports on atomic absorption, ICP, X-ray spectrometers, GLC, HPLC, ICP-MS, molecular fluorescence, UV-Vis-NIR, IR and CE. These are excellent source documents to facilitate the equipment qualification process. A current listing of these publications is given in Section 10.2. 

The analytical method for moisture determination must be validated before use during process validation studies. There are numerous techniques for moisture analysis that range from physical methods, such as loss on drying, to chemical methods, such as Karl Fisher titration. A comparative review of the conventional techniques are presented in an overview [32], The measurement of residual moisture is lyophilized pharmaceuticals by near-infrared (NIR) spectroscopy has recently been expanded [33]. 

NIR data were converted to compositions using the stover 5c rapid analytical method developed at NREL.129 The ability of the stover 5C methods to accurately measure the composition of corn stover feedstock is shown in Fig. 33.17, where the composition, as determined by NIR/PLS, is compared to measurement of the same samples using standard wet chemical methods. 

One source of prediction error is the inherent accuracy and precision of the reference analytical method used. If the reference method produces erroneous values that are consistently high or low, this bias will be reflected in the prediction results. Other sources of prediction error relate to the reproducibility, stability, and repeatability of the NIR instrument. Reproducibility (precision) is validated by making repeated measurements of the same sample and removing it between runs. Small changes in conditions may occur owing to multiple insertions of a sample onto the instrument. Stability refers to similar changes that may occur over... 

---