Near-infrared spectroscopy water analysis

Instrumental Methods. Water determinations probably tend to work well on instrumental analysis because water is radically different from other substances. Methods such as NMR and near-infrared spectroscopy are both applied to confectionery products. 

S.2.2.2 ICLS Example 2 This example discusses the determination of sodium hydroxide (caustic) concentration in an aqueous sample containing sodium hydroxide and a salt using NIR spearoscopy. An example of this problem in a chemical process occurs in process scrubbers where CO, is converted to Na,CO and H,S is converted to Na,S in the presence of caustic. Although caustic and salts have no distinct bands in the NIR, it has been demonstrated that they perturb the shape of the water bands (Watson and Baughman, 1984 Phelan et al., 1989)-Near-infrared spectroscopy is therefore a viable measurement technique. This method also has ad tages as an analytical technique for process analysis because of the stability of the instrumentation and the ability to use fiber-optic probes to multiplex tlie interferometers and Icx ate them rcm< >tely from the processes. 

FIGURE 31.18 Near Infrared Spectroscopy analysis provides clear delineation of the hydration profiles of emollient BW relative to water washing or lotion use. NIR shows good correlation with the visible appearance and clearer product differentiation compared to skicon. 

Near-Infrared Spectroscopy. Near-infrared (NIR) spectroscopy is a technique that has been around for some time but, like NMR spectroscopy, has only recently been improved and developed for on-line applications. Near-infrared analysis (NIRA) is a nondestructive technique that is versatile in the sense that it allows many constituents to be analyzed simultaneously 112, 113). The NIR spectrum of a sample depends upon the anharmonic bond vibrations of the constituent molecules. This condition means that the temperature, moisture content, bonding changes, and concentrations of various components in the sample can be determined simultaneously. In addition, scattering by particles such as sand and clay in the sample also allows (in principle) the determination of particle size distributions by NIRA. Such analyses can be used to determine the size of droplets in oil-water emulsions. 

Wine analysis is also feasible with near-infrared spectroscopy. This f. - technique provides a relatively straightforward method of analysing ethanol in wine. The O—bond in ethanol produces a near-infrared mode that is easily distinguished from the O—mode of water. In the... 

Malley, D. R, 1998. Near-infrared spectroscopy as a potential method for routine sediment analysis to improve rapidity and efficiency. Water Sci Technol. 37 181-188. 

A brief introduction to conventional qualitative and quantitative analysis of water-based polymer dispersions is followed by a demonstration of the use of near-infrared spectroscopy for the rapid identification and determination of water content. Use of the BC AP chemo-metric software package is discussed for library searching to identify unknown tests. It is shown how within a few minutes various polymer dispersions (about 50%) can be identified and their water content determined to a plus or minus 0.2% degree of precision. 5 refs. 

H. Buning-Pfaue. Analysis of water in food by near infrared spectroscopy. Food Chemistry 82 107-115,2003. 

Detailed near-infrared spectra of PET exposed to different relative humidities indicated three different subbands of the first overtone of water at 7080 cm 7010 cm and 6810 cm The comparison with the water spectmm of bulk water suggested that most of the water is only weakly bonded with PET (89). The analysis of difference spectra of dry nylon and nylon exposed to different humidities, indicated that there were distinct populations of hydrogen-bonded water in it (90). Recently, Musto et al. (91) investigated the nature of molecular interactions of water in epoxy resins by means of near-infrared spectroscopy as proposed by Eukuda et al. (89,90). They found three subbands at 7076 cm 6820 cm and 6535 cm evidencing two kinds of water adsorbed in the polymer (mobile water localized in micro vide and water molecules firmly bonded to the network). However, hydroxyl groups of epoxy may complicate the analysis of water content in polymers because they absorb also in the same overtone region as water. 

Dziki et al. (93) used near-infrared spectroscopy to characterize the mobility of water within the sarafloxacin crystal lattice differences in the location or orientation of the water molecules within the crystal were detected. The presence or absence of water in the crystal lattice can affect physical properties and processing ability. Analysis of near-infrared spectra of polymer samples allows us to distinguish between acceptable and unacceptable batches for formulation purposes. 

S. Lonardi, R. Viviani, L. Mosconi, et al., Dmg analysis by near-infrared reflectance spectroscopy. Determination of the active ingredient and water content in antibiotic powders, J. Pharm. Biomed. Anal., 7, 303-308 (1989). 

I venture to say that the majority of practical chemometrics applications in analytical chemistry are in the area of instrument specialization. The need to improve specificity of an analyzer depends on both the analytical technology and the application. For example, chemometrics is often applied to near-infrared (NIR) spectroscopy, due to the fact that the information in NIR spectra is generally non-specific for most applications. Chemometrics may not be critical for most ICP atomic emission or mass spectrometry applications because these techniques provide sufficient selectivity for most applications. On the other hand, there are some NIR applications that do not require chemometrics (e.g. many water analysis applications), and some ICP and mass spectrometry applications are likely where chemometrics is needed to provide sufficient selectivity. 

Schroeder SLM, Moggridge GD, Lambert RM, Rayment T (1997) Self-absorption effects in grazing-incidence total electron-yield XAS. J Phys IV 7 91-96 Segtnan VH, Sasic S, Isaksson T, Ozaki Y (2001) Studies on the Structure of Water Using Two-Dimensional Near-Infrared Correlation Spectroscopy and Principal Component Analysis. Anal Chem 73 3153-3161... 

Models are constructed in analytics to describe the relationship between responses and factors. This is, for example, important for optimization of analytical methods on the basis of response surface methods (cf. Section 4.2). Models are also needed for cahbration of analytical methods. There, calibration of a single analyte in dependence on one or several wavelengths might be of interest. If, in the first example, the straight-line model would be adequate, for the second task of multiwavelength spectroscopy, multivariate approaches are needed. Calibrations in the case of unselective analytical methods must also be performed. These methods are termed simultaneous multicomponent analysis. In near-infrared (NIR) spectroscopy, the contents of water and protein in whole grain wheat are determined that way. 

Near-infrared (NIR), the spectral region between 780 and 3000 nm, is characterized by broad and overlapping spectral peaks produced by the overtones and combinations of infrared vibrational modes. Figure 28.5 shows typical NIR absorption spectra of fat, water, and starch. Exploitation of this spectral region for in vivo analysis has been hindered by the same complexities of nonpulsatile tissue spectroscopy described above and is further confounded by the very broad and indistinct spectral features characteristic of the NIR. Despite these difficulties, NIR spectroscopy has garnered considerable attention, since it may enable the analysis of common analytes. 

Near-infrared (NIR) spectroscopy is widely used in the food industry as a fast routine analytical method for the quantitative measurement of water, proteins, fats and carbohydrates [13]. Although the near-infrared bands are less useful for qualitative analysis of foods because of their broad overlapped appearance, these bands are suitable for quantitative analysis when using chemometric techniques. Figure 8.12 illustrates the appearance of the major food components in the near-infrared, showing the spectrum of a sample of dehydrated tomato soup. 

The analysis of water in various media and under various conditions has been a major part of the field of near-infrared (IR) spectroscopy since its inception. The strength of the near-infrared absorption bands, the unique water combination band at 1940 nm, and the sensitivity of the absorption bands to the environment of the water molecules have all contributed to the success of near-infrared to smdy and measure water. 

B. Czarnik-Mamsewicz, K. Murayama, Y. Wu, Y. Ozaki. Protein-water interaction monitored by analysis of near infrared spectra. In Near Irfrared Spectroscopy. Proceedings of 11th International Conference, A. M. C. Davies, A. Garrido-Varo, eds. NIR Publications, Chichester, UK, 2004, p. 913-918. 

V. H. Segtnan, S. SaSid, T. Isaksson, Y. Ozaki. Studies on the structure of water using two-dimensional near-infrared correlation spectroscopy and principal component analysis. AnaZ Chem 73 3153-3161, 2001. 

Camacho, W., M. Hedenqvist, and S. Karlsson, Near Infrared (NIR) Spectroscopy Compared with Thermogravimetiic Analysis as a Tool for On-Line Prediction of Water Diffusion in Polyamide 6,6. Polym. Int., 2002. 51 1366-1370. 

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