Peter R. Griffiths

Resolution enhancement of diffuse reflectance i.r. spectra of coals by Fourier self-deconvolution: 1. C-H stretching and bending modes

Infrared spectra of many coal samples ranging from anthracites to lignites were measured by diffuse reflectance Fourier transform infrared spectrometry. The technique of Fourier self-deconvolution was applied to reduce the widths of all bands in the spectra. Several bands absorbing between 3000 and 2800 cm−1 due to C-H stretching modes of alkyl groups in different environments couId be resolved. In the spectral region between 900 and 700 cm−1, aromatic C-H out-of-plane deformation modes due to monocyclic and polycyclic rings could be distinguished after deconvolution.

Protein Conformation by Infrared Spectroscopy: Resolution Enhancement by Fourier Self-Deconvolution

Fourier self-deconvolution (FSD) has been employed to enhance the resolution of the infrared spectra of proteins in the solid state and in D2O solution. The feasibility of using diffuse reflectance spectrometry for measuring the infrared spectra of solid proteins has been demonstrated. FSD permits inherently broad absorption bands to be resolved into distinct peaks which can be associated with specific protein secondary structures. Because the areas of the resolved peaks are the same as the areas of the previously unidentifiable components, this new method should enable quantitative estimates of the proportion of each conformation in a protein to be calculated.

Infrared Microsampling by Diffuse Reflectance Fourier Transform Spectrometry

It is shown that diffuse reflectance techniques enable increased sensitivity to be obtained for infrared microsampling compared with the use of KBr micropellets. When nonabsorbing matrices, such as KCl, are used, detection limits of less than 10 ng of samples are observed. Samples absorbed on graphitized substrates, which have a fairly strong general absorption but few intense absorption bands, may also be studied but at somewhat reduced sensitivity. Diffuse reflectance infrared Fourier transform spectrometry does not appear to be particularly useful for studying adsorbates on silica gel, which is not only a strong infrared absorber but also has a surface which is so active that small changes in the surface structure can change the spectrum significantly. Extraction of sample spots from thin layer chromatography plates followed by deposition onto KCl yields much better results than in situ measurements.

Introduction to spectral deconvolution

Abstract An introduction to the theory of Fourier self-deconvolution is given. Using this technique, the widths of bands in an infrared spectrum may be reduced to the point that resolution of completely overlapping spectral features can be affected. The effects of noise and side-lobes are discussed, and methods to minimize each are described. The procedure required to deconvolve a spectrum is illustrated by a practical example.

Interpretation of Raman Spectra of Nitro-Containing Explosive Materials. Part I: Group Frequency and Structural Class Membership

Fourier transform (FT)-Raman spectroscopy has been used to obtain high-quality spectra of 32 explosive materials. The majority of the spectra of these explosives have not previously been reported. Twenty-eight of the explosives have been categorized into three classes (nitrates esters, nitro-aromatics, and nitramines) based on their chemical structure, the position of the antisymmetric and symmetric stretching vibrations of the nitro group, and the shapes of the band envelopes. The spectra of exceptional explosives are discussed in terms of their unique structures or compositions.

Raman Spectrometry with Fiber-Optic Sampling

Raman spectrometry has historically been limited to the study of pure, nonfluorescent samples. During the period 1966-1986, several workers demonstrated that the use of deep-red or near-infrared (NIR) lasers would allow the observation of Raman spectra without exciting fluorescence. The ability to obtain Raman spectra in the deep red or NIR could not be generally realized in reasonable measurement times, primarily because of the insensitivity of the available detectors (photomultiplier tubes or diode arrays). In addition, the krypton or solid-state ion-pumped lasers required for these measurements were very expensive.

Diffuse reflectance infrared spectrometry of powdered coals

Diffuse reflectance Fourier Transform infrared spectrometry has been shown to allow spectra of powdered coal samples to be measured at high sensitivity. Quantitative precision is good, so that the rank of individual coals and the composition of coal blends can be determined in <15 min. The degree of oxidation of coals, both for natural oxidation in the seam and for laboratory oxidation, can be determined from diffuse reflectance spectra of coals and from the second derivative of these spectra. Second-derivative spectra allow quantitative estimates of oxidation to be obtained without the application of spectral subtraction routines, which require standard reference samples that are not always available. The potential for using diffuse reflectance infrared spectrometry for monitoring reactions of powdered coals in-situ has been demonstrated.

Raman spectroscopic studies of explosive materials: towards a fieldable explosives detector

Abstract Raman spectroscopy, with red (632.8 nm) and near-infrared (785 and 1064 nm) excitation, has been used to obtain high quality spectra of neat explosives. Samples with dimensions from a minimum size of 10 μm have been analyzed utilizing a Raman microprobe fitted with a charge-coupled device (CCD) array detector. Little sample fluorescence is observed for 23 of the 32 high explosives using 632.8 nm excitation and all of the samples can be measured with a 1064 nm Nd:YAG laser. 785 nm radiation affords an excellent compromise between sensitivity and fluorescence suppression. Problems of instrumentation and sample handling have been investigated. Spectra have been obtained for explosives, both neat and in plastic and glass containers. The feasibility of sampling explosives through colored glass, which is highly fluorescent in the visible, is also demonstrated.

Retention behaviour of large polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography on a polymeric octadecylsilica stationary phase

Abstract Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and differential scanning calorimetry experiments were performed in order to study the retention mechanism in reversed-phase liquid chromatography for large polycyclic aromatic hydrocarbons. The effects of changing the mobile phase composition and column temperature were evaluated. The results suggest that a change in mobile phase composition from pure methanol to pure dichloromethane induces further non-planarity in non-planar solutes and also slightly changes the conformation of a polymeric octadecyl stationary phase. Conversely, a change to higher column temperatures drastically changes the structure of the stationary phase from solid-like to liquid-like, with only a small change of non-planar solutes to more non-planar conformations

Infrared Emission Spectroscopy. I. Basic Considerations

The basic principles behind the characterization of compounds by ir emission spectroscopy have been illustrated using surface films of silicone grease and gaseous samples. Anomalous features in the spectra are accounted for by considering the absorption of emitted radiation by less thermally excited molecules in the path to the detector. It is suggested that ir emission spectroscopy can be used easily to characterize thin layers on heated specular mirrors or hot vapors at low pressure, but care must be taken in the interpretation of results for thick layers of gases at high pressure, when the temperature of the emitter is close to that of the detector, or when molecules are to be characterized on substrates whose emissivity is high.