Quantitative absorption-reflection analysis

In situ quantitation The absorption photometric analysis was made in reflectance at 2 = 610 nm (Fig. 1). 

In situ quantitation The absorption photometric analysis in reflectance was carried out either at the absorption maximum of the pyrogallol derivative at = 350 nm (Fig. lA) or at the absorption maximum of the phloroglucinol derivative at = 420 nm (Fig. IB). 

Modern infrared (IR) spectroscopy is a versatile tool applied to the qualitative and quantitative determination of molecular species of all types. Its applications fall into three categories based on the spectral regions considered. Mid-IR (MIR) is by far the most widely used, with absorption, reflection, and emission spectra being employed for both qualitative and quantitative analysis. The NIR region is particularly used for routine quantitative determinations in complex samples, which is of interest in agriculture, food and feed, and, more recently, pharmaceutical industries. Determinations are usually based on diffuse reflectance measurements of untreated solid or liquid samples or, in some cases, on transmittance studies. Far-IR (FIR) is used primarily for absorption measurements of inorganic and metal-organic samples. 

Multivariate regression analysis plays an important role in modem process control analysis, particularly for quantitative UV-visible absorption spectrometry and near-IR reflectance analysis. It is conunon practice with these techniques to monitor absorbance, or reflectance, at several wavelengths and relate these individual measures to the concentration of some analyte. The results from a simple two-wavelength experiment serve to illustrate the details of multivariate regression and its application to multivariate calibration procedures. 

Due to the absorption bands in NIR being weaker than in UV-Vis absorption, NIR spectrometry is not as useful for quantitative measurements but offers better qualitative analysis because of improved selectivity. NIR techniques can handle both liquid and solid samples. Near infrared reflectance analysis (NIRA) has found wide application in process analysis, especially for highly absorbing compounds such as foodstuffs Coal, grain, pulp and paper products and some pharmaceuticals can also be determined by NIRA ". The reflectance from the sample is reported relative to reflectance from a standard reference surface. 

Absorption-reflection thickness IR spectroscopy (QUARTIR), quantitative, polymer wear analysis, 297... 

In situ quantitation The absorption-photometric determination in a reflectance mode was performed at A = 330 nm (detection limit ca. 40 ng per chromatogram zone). The fluorimetric analysis was carried out at =313 nm and An > 560 nm (detection limits ca. 10 ng per chromatogram zone) (Fig. 1). 

Complex Anisotropy is studied in texture goniometers (p. 193) as a function of sample orientation. If the study is aiming at quantitative analysis of scattering data, the absorption correction may become an issue. Conversely, by choosing a special kind of scanning modus (e.g., symmetrical reflection SAXS SRSAXS), the absorption correction problem can be simplified. 

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... 

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