Llewellyn Rintoul

Fourier transform Raman spectroscopy of polyacrylamide gels (PAGs) for radiation dosimetry

Polyacrylamide gels (PAGs) are used for magnetic resonance imaging radiation dosimetry. Fourier transform (FT) Raman spectroscopy studies were undertaken to investigate cross-linking changes during the copolymerization of polyacrylamide gels in the spectral range of 200-3500 cm(-1). Vibrational bands of 1285 cm(-1) and 1256 cm(-1) were assigned to acrylamide and bis-acrylamide single CH2 deltaCH2 binding modes. Bands were found to decrease in amplitude with increasing absorbed radiation dose as a result of copolymerization. Principal component regression was performed on FT-Raman spectra of PAG samples irradiated to 50 Gy. Two components were found to be sufficient to account for 98.7% of the variance in the data. Cross validation was used to establish the absorbed radiation dose of an unknown PAG sample from the FT-Raman spectra. The calculated correlation coefficient between measured and predictive samples was 0.997 with a standard error of estimate of 0.976 and a standard error of prediction of 1.140. Results demonstrate the potential of FT-Raman spectroscopy for ionizing radiation dosimetry using polyacrylamide gels.

Raman spectroscopy of urea and urea-intercalated kaolinites at 77 K.

The Raman spectra of urea and urea-intercalated kaolinites have been recorded at 77 K using a Renishaw Raman microprobe equipped with liquid nitrogen cooled microscope stage. The NH2 stretching modes of urea were observed as four bands at 3250, 3321, 3355 and 3425 cm(-1) at 77 K. These four bands are attributed to a change in conformation upon cooling to liquid nitrogen temperature. Upon intercalation of urea into both low and high defect kaolinites, only two bands were observed near 3390 and 3410 cm(-1). This is explained by hydrogen bonding between the amine groups of urea and oxygen atoms of the siloxane layer of kaolinite with only one urea conformation. When the intercalated low defect kaolinite was cooled to 77 K, the bands near 3700 cm(-1) attributed to the stretching modes of the inner surface hydroxyls disappeared and a new band was observed at 3615 cm(-1). This is explained by the breaking of hydrogen bonds involving OH groups of the gibbsite-like layer and formation of new bonds to the C=O group of the intercalated urea. Thus it is suggested that at low temperatures two kinds of hydrogen bonds are formed by urea molecules in urea-intercalated kaolinite.

Fourier transform infrared spectrometry: a versatile technique for real world samples†

The versatility of FTIR spectrometry was explored by considering a variety of samples drawn from industrial applications, materials science and biomedical research. These samples included polymeric insulators, bauxite ore, clay, human hair and human skin. A range of sampling techniques suitable for these samples is discussed, in particular FTIR microscopy, FTIR emission spectroscopy, attenuated total reflectance and photoacoustic FTIR spectrometry. The power of modern data processing techniques, particularly multivariate analysis, to extract useful information from spectral data is also illustrated.

Surface-enhanced Raman scattering of inorganic oxoanions

Abstract The surface-enhanced Raman scattering (SERS) of a series of sulfur oxoanions on a dry electrochemically roughened silver surface are reported. Spectra were recorded on an FT-Raman instrument using near IR excitation. The behavior of the anions falls into two categories. Sulfate and dithionate physisorb to the surface, give weak SER spectra that show few changes from the normal Raman spectrum. Sulfite and thiosulfate chemisorb to the surface, show large enhancement factors with significant changes to the spectrum. In particular, the similarity of the SER spectrum of the sulfite ion to the normal Raman spectrum of solid Ag 2 SO 3 suggests that a layer of Ag 2 SO 3 forms on the silver surface. For the chemisorbed anions, the method shows promise as an analytical technique with a limit of detection from solution of around 10 −4 M.

Interactions of iodoperfluorobenzene compounds with gold nanoparticles

Understanding the interactions of small molecules with gold nanoparticles is important for controlling their surface chemistry and, hence, how they can be used in specific applications. The interaction of iodoperfluorobenzene compounds with gold nanoparticles was investigated by UV-Vis difference spectroscopy, surface enhanced Raman spectroscopy (SERS) and Synchrotron X-ray photoelectron spectroscopy (XPS). Results from UV-Vis difference spectroscopy demonstrated that iodoperfluorobenzene compounds undergo charge transfer complexation with gold nanoparticles. SERS of the small molecule-gold nanoparticle adducts provided further evidence for formation of charge transfer complexes, while Synchrotron X-ray photoelectron spectroscopy provided evidence of the binding mechanism. Demonstration of interactions of iodoperfluorobenzene compounds with gold nanoparticles further expands the molecular toolbox that is available for functionalising gold nanoparticles and has significant potential for expanding the scope for generation of hybrid halogen bonded materials.

Raman microscopy of dickite, kaolinite and their intercalates

Raman microscopy has been used to study kaolinites and dickites and their intercalates and to identify dickites in kaolins at low concentrations. During the intercalation, with potassium acetate, of a low defect structure kaolinite, several crystals provided significantly different Raman spectra. This led to the proposition that during the kaolinite intercalation process, some dickite crystals in the kaolinite were also intercalated. Raman bands at 3631 and 3640 cm–1 for the dickite were observed, corresponding well with standard dickite bands. The kaolinite intercalate showed upon intercalation, an additional Raman band at 3605 cm–1 with a consequential marked decrease in the Raman intensity of the bands at 3652, 3670, 3684, and 3693 cm–1 assigned to the vibrational modes of the inner surface hydroxyl groups. Additional Raman bands for the intercalated dickite were observed at 3609 and 3599 cm–1. These bands are attributed to the formation of a strongly hydrogen bonded complex between the inner surface hydroxyl groups of dickite and the carboxyl groups of the potassium acetate. The intensity of the 3685 cm–1 band was reduced to a minimum and the other three inner surface hydroxyls with Raman bands at 3652, 3670, and 3693 cm–1 were absent in the dickite spectra. Pronounced changes in the low frequency region for both intercalates were observed.

Infrared Microspectroscopy of Bauxitic Pisoliths

Bauxite ore in the deposit at Weipa, Queensland, Australia occurs as pisoliths which are small, approximately spherical, pebbles with diameters in the range 0.5 to 2 cm. The distribution of various mineral species within the pisoliths has been determined by the use of reflectance infrared microspectroscopy of a large suite of pisoliths obtained from different parts of the Weipa orebody. The method allows the significant minerals of the bauxite to be analyzed including gibbsite (aluminium trihydroxide), boehmite (aluminium oxyhydroxide), quartz, and the clay, kaolinite. These minerals are readily distinguished by their IR spectrum. The iron minerals, present in small amounts, could not be detected. Specular reflectance spectra of sectioned pisoliths were measured, and the spectrum was utilized directly without the application of the Kramers–Kronig transformation. Polished pisolith sections were also mapped at a spatial resolution of 100 μm with the use of a computer-controlled microscope stage, and the mineral composition at any point was estimated by measuring relevant areas of the spectrum. Semi-quantitative results were obtained by relating the reflectance spectra for a particular pisolith thin section to the transmittance spectra for the same points. The transmittance spectra of the pisoliths were correlated with spectra of pure standards by application of a multicomponent Q-matrix approach. Principal component analysis of the mineral distribution data allowed the suite of pisoliths to be subdivided into groups with similar mineralization.

A spectroscopic study of thalassemic gallstones

The chemical composition of a suite of pigment gallstones obtained from patients suffering from β-thalassemia was studied using FTIR, FT-Raman, and Mossbauer spectroscopies with a view to gaining a better understanding of their complex composition and developing an effective characterization procedure. The combination of vibrational spectroscopic techniques such as FTIR and FT-Raman make it possible to identify the major chemical components of thalassemic pigment stones and to subcategorize them for further study. All but one sample had almost identical FTIR spectra where bands attributable to both cholesterol and various bilirubinate salts were observed. One sample, low in cholesterol, showed, distinctive spectral peaks of calcitic CaCO3. This sample was sufficiently high in iron for Mossbauer spectroscopy, which showed, at room temperature, a quadrupole-split doublet consistent with the presence of iron (III). This concomitant presence of iron and a high CaCO3/low cholesterol content has, as far as we are aware, not been previously reported. When studied by FT-Raman, however, most of the stones gave spectra typical of previously characterized brown stones. Due to the limited number of stones available, in particular iron-rich samples, further work is required, but these preliminary results indicate that it may in fact be possible to unequivocally categorize thalassemic stones into different types using spectroscopic techniques. Together with FTIR and Raman microscopy of cut stones, such nondestructive spectroscopic techniques show promise in helping researchers gain an understanding of thalassemic stone formation and occurrence. In addition, the samples are maintained for further study, which is important considering the difficulty in establishing large suites of such special category stones.

Raman Microspectroscopic Mapping: A Tool for the Characterisation of Polymer Surfaces

Raman mapping by point illumination of polymer surfaces is discussed with examples taken from the plasma treatment of polypropylene (PP) and subsequent grafting of polystyrene (PS). Maps can be constructed for surface properties such as crystallinity, blend components and distribution of grafted PS. The Raman sampling volume was estimated for confocal operation using a 50x objective lens.

A DRIFTS study of reactive dye states on cotton fabric

Abstract A diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) investigation was performed on a series of poplin cotton fabrics treated with a bifunctional reactive dye of unknown chemical structure and composition, and in different states on the substrate (unfixed or fixed to the cotton substrate as well as chemically treated). The cotton-cellulose bands (log 1/ R ) dominate the spectra of the dyed fabric samples, and this leads to difficulties in the discrimination and matching of such spectra. However, it is demonstrated that qualitative discrimination is achieved by using principal component analysis (PCA). The dye state is the basis for this; also, within the % dye concentration series separation of spectra is observed according to the amount of the dye present. Exploratory quantitative analysis of such samples, attempted with partial least squares (PLS) regression, shows that it may be possible to predict the % concentrations with larger calibration sets. Further, series of fabrics were dyed with different reactive dyes and again treated to obtain various reactive dye states. The DRIFT spectra of these fabrics were submitted to PCA, with qualitative discrimination being achieved on the basis of dye colour and the reactive dye state. It is shown that the spectra of the unfixed dyes are similar to those of the neat dye powders. This study indicates that DRIFTS may be useful for matching, discrimination and prediction of reactive dyes on cotton substrates even if the dye structure is unavailable. This points to potential applications in the dye and general textile industry as well as specific forensic cases involving relatively large samples. In addition, it is clear that further carefully designed experiments may lead to a clarification of the details of binding of polyfunctional reactive dyes on cotton.