Infrared spectroscopy absorption values

Infrared spectra of fats and oils are similar regardless of their composition. The principal absorption seen is the carbonyl stretching peak which is virtually identical for all triglyceride oils. The most common appHcation of infrared spectroscopy is the determination of trans fatty acids occurring in a partially hydrogenated fat (58,59). Absorption at 965 - 975 cm is unique to the trans functionaHty. Near infrared spectroscopy has been utilized for simultaneous quantitation of fat, protein, and moisture in grain samples (60). The technique has also been reported to be useful for instmmental determination of iodine value (61). 

If i = i — ik] and H2 = ns — are known as a function of wavelength, Eq. 12 can be used to calculate the entire RAIR spectrum of a surface film. Since transmission infrared spectroscopy mostly measures k, differences between transmission and RAIR spectra can be identified. Fig. 6 shows a spectrum that was synthesized assuming two Lorentzian-shaped absorption bands of the same intensity but separated by 25 cm. The corresponding spectrum of i values was calculated from the k spectrum using the Kramers-Kronig transformation and is also shown in Fig. 6. The RAIR spectrum was calculated from the ti and k spectra using Eqs. 11 and 12 and is shown in Fig. 7. 

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%). 

Analysis for total petroleum hydrocarbons (EPA Method 418.1) provides a one-number value of the petroleum hydrocarbons in a given environmental medium. It does not, however, provide information on the composition (i.e., individual constituents) of the hydrocarbon mixture. The amount of hydrocarbon contaminants measured by this method depends on the ability of the solvent used to extract the hydrocarbon from the environmental media and the absorption of infrared light (infrared spectroscopy) by the hydrocarbons in the solvent extract. The method is not specific to hydrocarbons and does not always indicate petroleum contamination, since humic acid, a nonpetroleum material and a constituents of many soils, can be detected by this method. 

The term 1 or h indicates low or high coverage of adsorbed ethene, as inferred from ethene exposures.h TPD, temperature-programmed desorption LITD, laser-induced thermal desorption 1 FT-MS, Fourier-transform mass spectrometry SIMS, secondary-ion mass spectrometry MS, mass spectrometry T-NEXAFS, transient near-edge X-ray absorption fine structure spectroscopy RAIRS, reflection-absorption infrared spectroscopy. d Data for perdeut-erio species.1 Estimated value. 

The association constant of pyridazine with ethanol was found to be 4.9 (from electronic absorption spectra) and 6.8 (infrared absorption spectra), and the corresponding values for the strength of the hydrogen bond are 4.2 and 4.6 kcal. The hydrogen-bonded form of P3n-idazine was considered to comprise one alcohol at one azine-nitrogen at small mole ratios of alcohol to azine and to involve the second nitrogen at high mole ratios (an additional shift in the electronic spectrum. The association constants (3.1-3.8) of pyridine, quinoline, and isoquinoline with methanol in carbon tetrachloride have been determined by infrared spectroscopy. 

The fact that both the COad bands and the CO2 band appeared in the same direction on an nm-Ru/GC electrode illustrates one of the main characteristics of the AIREs. It may be worth noting that the COl band center measured in Figure 11(a) is close to that reported by Lin et al. but is about 15cm lower than the value for CO adsorbed on a massive Ru electrode in CO saturated 0.5 M HCIO4 solution studied by using electromodulated infrared spectroscopy (EMIRS) [50]. It is evident that the appearance of the COb band in the spectrum of the nm-Ru/GC electrode is due to significant enhancement of IR absorption. 

A major difference between infrared and ultraviolet spectroscopy is in the concentrations required for assay In infrared spectroscopy as much as a 10% w/v solution of sample must be prepared. This means that the path length of the cells used in infrared must be very short, usually 0.025-0.1 mm (otherwise absorbance values would be too high). Another problem with infrared spectra is that the solvent used in the assay (usually chloroform or dichloromethane) also possesses chemical bonds that will absorb infrared radiation in some part of the spectrum, obscuring the absorption by the sample at these wavelengths. Samples are prepared in solution, in a mull or paste made with liquid paraffin (Nujol), or in a solid disc prepared by trituration with dry potassium bromide followed by compression in a hydraulic press. 

Cyclo-(Gly-Sar) (80), Cyclo-(Sar2) (81) and the analogous linear peptide acetyl sarcosine dimethylamide (AcSarDMA) (81) were dissolved in chloroform and their interactions with iodine were investigated. The complex formed exhibited a new absorption at 480 nm for Cyclo-(Sar2)-l2 and at 363 nm for AcSarDMA-l2. The limited solubility of Cyclo-(Gly-Sar) in chloroform made it difficult to detect new absorption due to complexes with iodine. In either case, on mixing iodine with peptide the absorption due to iodine at 510 nm decreased and a distinct isosbestic point was observed, which enabled us to determine the equilibrium constant K for the complex formation. K values are listed in Table 2. K for AcSarDMA-l2 is greater than K for Cyclo-(Sar2)-l2- Investi tions by infrared spectroscopy showed that the... 

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