Water bands

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... 

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. 

Extensive interpretation is not possible because the efifects of the salt, caustic, and temperature are manifested as complex perturbations on the water band. 

FIGURE 13 Collection of NIR spectra. The varying water band near 1950 nm can be clearly identified. 

Figure 1A shows the FTIR spectrum of a freshly prepared 0.36 M solution of TMMS in 10% water-acetone. The Si—O—C methoxy asymmetric stretch band (1083 cm-1) and the symmetric stretch band (865 cm-1) are clearly identified along with a water band. After a sufficient delay which depends on the solution pH, the Si—O—C bands disappear, as shown in Fig. IB, indicating complete hydrolysis of the methoxy group, and are replaced by the C—O stretch of methanol (1031 cm-1) and the Si—OH stretch (896 cm-1) of the silanol group. After further standing, the Si—OH band is reduced and the Si—O—Si asymmetric stretch (1043 cm-1) is present, as shown in Fig. 1C. Thus, the...

An analysis of the IR fundamental water bands is more complicated. But experienced authors-agree with the overtone results very well. The papers on band analysis of the OH stretching fundamental band given by Mikhailov and Zolotarev19 (Vol. 3, p. 15.) is consistent with our analysis of the HOD 1. overtone stretching vibration50. ... 

An extension of linear regression, MLR involves the use of more than one independent variable. Such a technique can be very effective if it is suspected that the information contained in a single independent variable (X) is insufficient to explain the variation in the dependent variable (Y). For example, it is suspected that a single integrated absorbance of the NIR water band at 1920 nm is insufficient to provide accurate concentrations of water contents in process samples. Such a situation can occur for several reasons, such as the presence of other varying chemical components in the sample that interfere with the 1920-nm band. In such cases, it is necessary to use more than one band in the spectrum to build an effective calibration model, so that the effects of such interferences can be compensated. 

Subtraction of the spectrum of liquid water, even of moderate band intensity, can also be complicated by solute-water interactions which cause a shift in the H-O-H bending bands, making a complete nulling of the band in the difference spectrum impossible (23). As discussed further below, in bulk phase samples such as microemulsions or inverse micelles of moderate water content, significant information about aggregate structure is obtained from shifts in the water bands. 

Organics and liquid 1 0 are intimately associated in skeletal carbonates, so much so that often the most obvious effect of bleaching or decay of organics on the spectral properties of biogenic carbonate samples is a decrease in the intensities of the liquid water bands. This is illustrated in ratio spectra in Figures and 6. A ratio of two spectra provides a spectrum of phases present in one sample but absent in the other. As can be seen, all the ratio spectra contain features due to liquid water. 

The vibrational spectrum of H+ is even harder to interpret. Absorption increases at all frequencies in the infrared and the already broad water bands get broader, but not symmetrically. The additions to the water bands have been interpreted as the new bands of the HsO+ unit in H+ (Falk and Gigufere, 1957). The suggested frequencies are shown in Table 9. On the other hand it has been suggested that the rapid proton shifts from one oxygen to another precludes a band spectrum for that unit in water (Ackermann, 1961) and its absorption has been... 

One of the most common uses of subtraction techniques is to remove a solvent spectrum from the spectrum of a solution. In most every case there is a solute-solvent interaction, and the spectra of all components in the solution have changed from those of the pure compounds. The changes can occur in band frequencies, intensities, and shapes. The user may gain some insight by performing the subtraction, but the spectra will be distorted. Examples of typical distortions are shown in Fig. 5-7 (6). The top spectrum is a mixture of EDTA and water, and the second spectrum is that of pure water. Two substractions are shown. The first was based on removal of the water band... 

Cation exchange has an effect on the quantity of the interlayer water, especially on the hydrate water of cations. The transmittance of the adsorbed water band (3600 cm-1) and the hydrate water band (3450 cm1) as a function pH is shown in Figure 2.25. 

Bound or unbound water in a molecule can give rise to sharp or broad bands. In alkali halide disks a water band at 3350 cm" may appear Lens tissues... 

Figure 2 shows the FT-IR spectra of kaolin and MK-600 metakaolin and the samples treated at 90 C (the treatment at room temperature did not modify the metakaolin). The spectrum of the metakaolin shows the structural changes produced during the calcination. The four Al-OH stretching bands, from 3700 to 3600 cm [21-24], disappear due to the dehydroxylation, the water bands being observed at 3470 and 1630 cm. ... 

Recent infrared spectra of the shifted suppressed water bands indicate that the surface of Europa contains hydrated minerals. These have been suggested to be hydrated salts and organics, which would also be consistent with material from an underground ocean. Because of this strong, but indirect, evidence for an ocean, Europa is now considered to be an object on which biological materials could have evolved. Such an evolution, if it occurred, could have been driven by the heat created by the tidal interaction with Jupiter, although recently this has been suggested to be too small. 

Recent data from the near IR mapping spectrometer (NIMS) of the Galileo spacecraft has also identified areas on the moons in which the water bands axe shifted and suppressed, consistent with large surface areas... 

All complexes with water molecules in formula have water bands at 3350 and 1625 cm. i. 

The infrared spectra of the OMPA complexes of (111), Eu(lll), and Tb(lll) were obtained both before and after the complexes had been heated at 100 °C. under vacuum for several hours. After the heat treatment, the water bands were less intense, the P—O—P band was smoothed out in the (III) complex, and the P—N bands were unchanged. Since the water bands did not disappear after the heat treatment, at least part of the water molecules are tightly held. 

The visible spectrum in chloroform consists of a split peak /presumably/Tig(F) Tig(P) at 515 and 493 mp (e 31) with a shoulder at 468 m/x identical with that obtained for a mixture of it and the dimethanol addition compound]. The infrared spectrum is substantially the same as that of the anhydrous compound except for water bands. 

K. Nakamura. Science Repts. Tohoku Univ., First Set. 35, 1-10 (1951). Raman structure of liquid water, band shapes, pure, alcohol solutions, 10-45 G. 

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