J. E. Katon

The identification of fibers by infrared and Raman microspectroscopy

Abstract The application of Raman and infrared microspectroscopy to fiber identification has been investigated. Natural and synthetic fibers, both organic and inorganic in nature, can be rapidly characterized by these techniques. In general, it has been found that infrared microspectroscopy offers a nonsubjective method of fiber identification that is quicker, easier, and occasionally, more selective than classical methods. Raman microspectroscopy has also been proven useful for these analyses. It provides low-frequency information, requires virtually no sample preparation, and supplies data complementary to that furnished by infrared microspectroscopy. In many cases one may use these methods for a quick differentiation of fibers of the same type which have undergone different chemical treatments.

Aqueous Infrared Pharmaceutical Analysis of Two Choline Compounds by Flow Injection Analysis Using the CIRCLE Cell

The advent of the cylindrical internal reflectance (CIRCLE) cell has solved the difficult problem of quantitation of solutes in aqueous solutions by infrared spectroscopy. By a combination of flow injection analysis (FIA) and Fourier transform infrared (FT-IR) spectroscopy with the CIRCLE cell, a fast, reproducible technique suited for the determination of two choline compounds of pharmaceutical interest—succinylcholine chloride and bethanechol chloride—was developed. Quantitation was carried out with the use of either the ester band at 1075 cm−1 for bethanechol or the trimethyl quaternary ammonium band at 953 cm−1 for succinylcholine. Linearity of standard solutions was achieved from about 0.5 to at least 50 ppt for both compounds, and detection limits of 0.02% w/v were possible. A sample throughput of 60 samples/h was estimated. Analysis of pharmaceutical preparations was performed after minor sample clean-up, which was necessary only in the case of the bethanechol chloride tablets.

Diffraction-Induced Stray Light in Infrared Microspectroscopy and Its Effect on Spatial Resolution

Model experiments were conducted in an effort to quantitatively assess the extent of stray light, resulting from diffraction, in an FT-IR microscope system. The effects of stray light were studied under conditions employing different aperturing modes, aperture sizes, and wavelengths of light. Results and consequences of the findings are discussed with respect to the spatial resolution and quantitative integrity of the data obtainable in mapping analyses of multilayer polymer laminates.

Infrared and Raman Group Frequencies of Cyclic Imides

Infrared and Raman spectra of several examples of each of three classes of cyclic imides have been examined. Spectra-structure correlations have been sought for each of the classes, with particular emphasis being placed on the 1600–1800 cm−1 region. The spectra in this region are often complex, reflecting subtle structural features in the condensed phases. Group frequencies for substituted succinimides, phthalimides, and maleimides are proposed.

Structure, hydrogen bonding and vibrational spectra of pyruvic acid

Abstract The complete vibrational spectra of liquid pyruvic acid and the infrared spectrum of crystalline pyruvic acid at about 20 K have been recorded and analyzed. A vibrational assignment is proposed based on these spectra and comparison with spectra of derivatives of pyruvic acid. The spectra of pyruvic acid can best be interpreted in terms of a cyclic hydrogen-bonded dimer structure in which the two carbonyl groups are in a trans configuration in the pure liquid phase. A similar structure has been reported for crystalline pyruvic acid by X-ray diffraction. In dilute solution the structure appears to be monomeric with an internal hydrogen bond, in essential agreement with the structures of the monomer reported from microwave spectroscopic measurements.

Infrared Spectra of Crystalline Acetic Acid, a Hydrogen-Bonded Polymer

The polarized infrared spectra of crystalline acetic acid and two of its deuterated derivatives, CH3COOD and CD3COOD, have been recorded from 400 to 4000 cm−1 at cryogenic temperatures. The spectroscopic results have been interpreted on the basis of a factor group analysis based on two structural models: a crystallographic cell composed of four interacting monomer units some of whose vibrational modes are highly perturbed by hydrogen bonding and a unit cell composed of two noninteracting acetic acid chains. The results are discussed in terms of possible interactions between the hydrogen-bonded acetic acid polymeric chains.

The vibrational spectra and structure of α-chloroacetic acid

Author Institution: Chemistry Department, Miami University; Chemistry Department, Battelle Memorial Institute

Use of Molecular Microspectroscopy to Characterize Pigment-Loaded Polypropylene Single Fibers:

Molecular microspectroscopy was used to characterize different pigments loaded into polypropylene fibers. Single-fiber analysis by infrared, visible, and Raman microspectroscopies proved to be quite complementary for identification and quantitation of these materials. Infrared microspectroscopy was effective not only for identification of pigments loaded into the fibers, but also for quantitation of concentration levels at 1% (w/w) and greater. Visible microspectroscopy was effective for quantitation of pigment levels between the range of 0.1 and 1% (w/w). However, it may not be successful for positive identification of most pigments. Raman microspectroscopy was an effective technique for pigment identification and quantitation over all examined concentration levels provided that the sample showed no signs of fluorescence or heating effects. Quantitation for all techniques gave correlation coefficient values of 0.99+ and relative standard deviations typically ranging from 5 to 20%.

Characteristic Infrared Absorption Frequencies of the Enol Group of 1,3-Dicarbonyl Compounds

Infrared spectra of several 1,3-dicarbonyl compounds from different organic chemical clauses have been recorded. Assignments of characteristic enol frequencies have been made, and group frequency ranges developed. In most cases, the ranges are reasonably narrow considering the great changes in overall structure of the examples studied. The enol structure affects to a significant degree the absorption frequencies of certain modes.

The Development of a Fourier Transform Raman Microprobe

An FT-Raman microprobe based on a refracting microscope and proprietary beamsplitter is detailed and characterized with regard to spatial resolution, Rayleigh rejection, and performance as compared to a 180° backscattering macro-geometry. Several examples are presented which demonstrate the microprobes capabilities in analyzing micro-samples with moderate Raman-scattering cross sections. Further improvements to the integrated system are also discussed and highlighted.