Infrared internal reflectance

The ATR technique is a commonly used infrared internal reflection sampling technique. It samples only the surface layer in contact with the ATR element the sampling depth probed is typically of the order of 0.3-3 pm [1]. Unless software corrected, compared with a transmission spectrum, the relative intensity of bands within an ATR spectrum increase in intensity with decreasing wavenumber. Several FTIR instrument companies now supply "ATR-correction" software developed to correct for the different relative intensities of bands observed between ATR and transmission spectra, so that ATR spectra can be more easily compared to and searched against transmission spectra. 

Adsorption of Proteins and Polysaccharides at Aqueous—Solid Interfaces by Infrared Internal Reflection Spectrometry In Situ Investigation... 

Let us call this the donor-acceptor complex proposal, similar to that presented recently for adsorption of substituted nitrobenzenes and nitrophenols on mineral surfaces [739]. The experiments on which this proposal is based are (1) isotherms of phenol, nitrobenzene, and m- and / -nitrophenol on one commercial activated carbon at pH = 2-7 and very low solute concentrations ( <1.5% of the solubility limit of these species [6]) and (2) detailed infrared (internal reflection) spectroscopic analysis of the surface after adsorption of / -nitrophenol. Interestingly, neither in this study, nor in any subsequent study that supports this mechanism, has a similar analysis been performed with carbons containing varying concentrations of carbonyl surface groups. Also of interest is that the authors dismiss the electrostatic explanation of the reported pH effects by assuming that the isoelectric point of the carbon (which was dried at 200°C for 12-24 h) was ca. 2.4. 

E. D. Palik and R. T. Holm, Electric field modulated infrared internal reflection study of the sihcon-electrolyte interface, 7. Phys. 56(1), 843, 1984. 

Methods for micro-measurement of surface areas include the Brunauer, Emmett, and Teller (BET) method (2), which relies on the adsorption of monolayers of gas, commonly nitrogen or argon, the adsorption of organic molecules such as ethylene glycol and ethylene glycol monoethyl ether (EGME) (10). and the use of infrared internal reflectance spectroscopy (11) which characterizes bonding of sorbed water. These last two techniques have been confined principally to surface areas of clay minerals. 

The Infrared Internal Reflectance Approach An interesting alternative method of minimizing the solution path-length is to employ internal reflectance or attenuated total reflectance (ATR) and this was the approach adopted by the authors of the first report on the acquisition of in situ infrared spectra Mark and Pons [39] employed the ATR approach, [or, as they termed it, frustrated multiple internal reflection (MIR)-see below], to... 

Liquids may be sampled as neat liquids or in solution. A mid-infrared transmission spectrum sufficient for chemical identification may often be recorded from a capillary layer of a nonvolatile, pure liquid. This may be prepared simply from a drop of the liquid that has been sandwiched between a pair of mid-infrared transparent windows clamped together, which is also resistant to attack by the liquid. A more reproducible (and safer) practice, however, is to use an appropriate pathlength cell. Whichever method is selected, the specimen examined must be free from bubbles. For strongly absorbing liquids and some quantitative applications, a more efficient approach may be to use an appropriate infrared internal reflection technique accessory. 

Internal reflection spectroscopy of solids Mid-infrared internal reflection accessories were developed initially largely for studying the surface layer characteristics of a continuous flat solid sample, e.g., a polymer film although they may also be used as convenient methods of sample identification, when a surface layer spectrum may be taken as indicative of a sample s bulk characteristics. The sample surface is brought and held under low pressure into optical contact with the clean surface of an internal reflection element. Other common traditional uses have included the direct examination of fibers, foams, and malleable (soft) powders. It has, however, become common practice nowadays, with the sensitivity now available with FT-IR spectroscopy, to use single (or low-number) internal reflection accessories to conveniently and easily record a mid-infrared fingerprint... 

The first infrared spectroelectrochemistry was reported in 1966 by Harry Mark and Stan Pons (30). As a postdoc at Cal Tech with Fred Anson, Mark (Figure 6) had visited Kuwana at Riverside — a visit that sparked his interest in spectroelectrochemistry. He also visited the electrochemistry group at the Science Center where he discussed internal reflection spectroelectrochemistry with Hansen. Upon his arrival at the University of Michigan as an assistant professor, Mark decided to try to develop infrared internal reflection spectroelectrochemistry because of the structural information in an infrared spectrum. He was able to persuade Paul Wilks (Wilks Scientific Corp.) to lend him a double beam internal reflectance attachment. A Ge internal reflectance plate-electrode was made by Recticon Corp. from n-type semiconducting Ge, which was already known to function as a working electrode (31,32). Stan Pons, a first year graduate student, performed the experimental work in which the spectra of the reduction products of 8-quinolinol and tetramethylbenzidine free radical were chracterized. 

Attenuated Total Infrared Internal Reflectance (ATR) Spectroscopy (Spectra-Tech)... 

Mirabella FM, Fitzpatrick J, Reffner JA, Chabal YJ (2002) Mid-Infrared internal reflection spectroscopy. In Griffiths PR,Chalmers J (eds) Handbook of Vibrational Spectroscopy, vol 2. Wiley, Chichester, pp 1091—1123... 

Table 15.1. Common Materials Used as Mid-Infrared Internal Reflection Elements with Critical Angle when ni = 1.5...

Infrared internal reflection spectroscopy was used by Brash and Lyman to study the adsorption of the plasma proteins, albumin, y-glcbu-lin, and fibrinogen, on a variety of hydrophobic polymer surfaces. The results indicated that all the proteins investigated behaved rather similarly on a variety of hydrophobic surfaces. Under static conditions the proteins appeared to be rapidly adsorbed as monomolecular layers from solutions varying in concentration from a few milligram percent to the concentration levels of normal plasma. They deduced these monolayers to be closely packed arrays in which the protein molecules appeared to retain their native globular form. 

Figure 13. Adsorption of plasma proteins on polyethylene at 310 K measured by infrared internal reflection spectroscopy —, fibrinogen —, y-globulin, - - albumin. (Adapted from Brash and Lyman. )...

M.J.D. Low and R.T. Yang, "Quantitative Analysis of Aqueous Nitrite/Nitrite Solutions by Infrared Internal Reflectance Spectrometry". Anal. Chem., 45, 2014 (1973). 

R.T. Yant and M.J.D. Low, "Infrared Internal Reflection Spectra of Methanol-Water Mixtures". Spectrochimica Acta, 30a, 1787 (1974). 

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