Combination bands water

The latter applies to NIR spectroscopy used for the non-invasive determination of blood glucose by means of a fibre-optical measuring-head (Jagemann et al. [1995] Muller et al. [1997] Danzer et al. [1998]). In addition to the weak overtone and combination bands resulting from glucose, strongly disturbing absorption of water, that is the main component... 

There is a strong water combination band in this region so the band could be related to this, but it shows potential-dependent behaviour and hence must be a surface species. 

The near-IR technique has been used very successfully for moisture determination, whole tablet assay, and blending validation [23]. These methods are typically easy to develop and validate, and far easier to run than more traditional assay methods. Using the overtone and combination bands of water, it was possible to develop near-IR methods whose accuracy was equivalent to that obtained using Karl-Fischer titration. The distinction among tablets of differing potencies could be performed very easily and, unlike HPLC methods, did not require destruction of the analyte materials to obtain a result. 

Near-infrared spectroscopy is quickly becoming a preferred technique for the quantitative identification of an active component within a formulated tablet. In addition, the same spectroscopic measurement can be used to determine water content since the combination band of water displays a fairly large absorption band in the near-IR. In one such study [41] the concentration of ceftazidime pentahydrate and water content in physical mixtures has been determined. Due to the ease of sample preparation, near-IR spectra were collected on 20 samples, and subsequent calibration curves were constructed for active ingredient and water content. An interesting aspect of this study was the determination that the calibration samples must be representative of the production process. When calibration curves were constructed from laboratory samples only, significant prediction errors were noted. When, however, calibration curves were constructed from laboratory and production samples, realistic prediction values were determined ( 5%). 

Wirzing 216a, 216b) found that the combination bands in the near infrared were particularly well-suited for the distinction of silanol groups and water. Bands were observed at 4545-4365 cm and at... 

Fig. 12. Combination band of water in water methanol mixtures (A = 20 HjO/liter methanol) diluted with CC14. Parameter ml of A per liter CCI4. 20 °C, d= 10 cm, methanol spectrum sub stracted by compensation82)...

Fig. 14. IR combination band of water in dioxan mixtures diluted with CCI4 at 20 °C. Numbers on the curves give the amount of the mixture A per liter CCI4, cd = 500 (g 1 1 cm)82)...

Fig. 30. Upper Combination band v + v2 of water. Lower Absorption band of water in collagen during drying142 . The most dried sample 3 shows a A similar to supercooled water at - 20 °C...

Figure 3. Overtone and combination band spectrum oj ethylene and water adsorbed on Mn"A zeolite. The ethylene bands lie close to the gaseous (V -f- vn), (vt + vs), 2vlu and 2vs vibrational modes, indicating that the ethylene molecule has retained its chemical composition and structural integrity (-, 1) MnA 4- ethylene (-------------------,2) MnA hydrated CtHt (g) bands.

Glucose absorption at physiological concentrations is several orders of magnitude lower than that from water, which is the major background absorber in tissue. In addition, molecular overtone and combination bands are typically broad, leading to overlapping, yet distinctive, spectral features.44 As a result of this spectral overlap, multivariate calibration techniques are required to extract quantitative analyte-specific information.45... 

Compared to the measurement of VCD the measurement of optical activity in the Raman spectrum offers all the well known advantages that Raman spectroscopy has over infrared spectroscopy the use of the inexpensive glass as the sample cell, and the occu-rance of fewer bands, overtones and combination bands are reduced in intensity, thereby diminishing the possibility of overlap. Very important also is the fact that water is usable as solvent. 

Somewhat more complicated than the complexes discussed earlier is the combination of water with ammonia. The IR spectral characteristics of this complex were calculated using a variety of basis sets and the results are presented in Table 3.49. Also presented in this table are comparable data computed at a correlated (MP2) leveF, for purposes of comparison. The red shift of the proton donor water molecule v. band is 103 cm , quite a bit lower... 

FIGURE 4 Near-infrared spectra of a-lactose monohydrate (solid trace) and /Mactose anhydrate (dashed trace), highlighting the strong water combination band at 1940 nm. The figure was adapted from data presented in reference 80. 

In 1970, Warren et al. addressed the determination of trace amounts of water in mono-, di-. and triglycerides by NIR spectrometery [7]. Using chloroform as a solvent, the investigators studied the combination band of water occurring at 1896 nm in the presence of the -OH groups on glycerides to determine water down to 0.05%. 

Acetonitrile (ACN) possesses some unique properties, such as a high dielectric constant (35.95) and the solubilization of many inorganic and organic materials . It is actually one of the few simple aprotic solvents miscible in water at any ratio. X-ray diffraction studies of pure acetonitrile revealed that ACN molecules do not strongly interact with themselves and are only weakly associated via dipole-dipole interaction . The IR spectrum of pure acetonitrile includes two major bands placed at 2257 and 2295 cm . The former, called V2, originates from the C=N stretching mode while the latter is a combination band composed of the CCH bend V3 and C—C stretch V4 modes. ... 

From this point of view the water molecule has been particularly well studied. To a first approximation the band which appears around 5154 cm (1940 nm, see Figure 10.24) resuits from the combination of the asymmetrical vibration situated at 3500 cm and the deformation vibration (scissoring, see Section 10.6) at 1645 cm (Figure 10.16). These simpie caicuiations (3500 + 1645 = 5145) are an imperfect approach, which conceais a certain number of factors of the physical state of the compounds to which infrared is sensitive. Among the approximations are those for the combination bands of the bonds C-H, N-H and C-0 in the near-IR. 

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