Study of normal colorectal tissue by FT-Raman spectroscopy

FT-Raman spectroscopy was employed to study normal human colorectal tissues in vitro with the aim of evaluating the spectral differences of the complex colon mucous in order to establish a characteristic Raman spectrum. The samples were collected from 39 patients, providing 144 spectra for the statistical analysis. The results enable one to estabilish three well-defined spectroscopic groups of non-altered coloretal tissues that were consistently checked by statistical (clustering) and biological (histopathology) analyses: group 1 is represented by samples with the presence of epithelial layer, connective tissue papillae, and smooth muscle tissue; group 2 comprises tissues with epithelial layer and connective tissue papillae; group 3 presented mostly fatty and slack conjunctive tissue. The study reveals the existence of an intrinsic spectral variability for each patient that must be considered when sampling tissues fragments to build a spectral database. This is the first step for future studies and applications of Raman spectroscopy to optical biopsy and diagnosis of colorectal cancer.     

FT-Raman spectroscopy of biological molecules

Raman spectroscopy of biological molecules is often very difficult if not impossible due to a large fluorescence background from absorbing species, either from the molecule itself or an impurity. Photobleaching is occasionally successful in photochemically removing fluorescent impurities, but the majority of samples are not responsive to such treatment. Resonance enhancement of an absorbing species allows acquisition of Raman spectra in spite of competing fluorescence. However, the resonance Raman spectrum is characteristic of the chromophore only and little structural information is obtained from the spectrum about other parts of the molecule which are not resonantly enhanced. The newly developed technique of FT-Raman spectroscopy proves to be a solution to both of these problems for biological materials. Excitation with infrared wavelengths prevents electronic absorptions which give rise to fluorescence. In addition, the obtained spectra are completely nonresonant, allowing detection of vibrational modes of all parts of the molecule including the chromophore. We will present nonresonant, fluorescence free spectra of a range of biologically significant molecules including phospholipids and porphyrins.     

Quantitative determination of silicon in silica dust by FT-Raman spectroscopy

Silicon was quantitatively determined in respirable silica dusts and silica fume by FT-Raman spectroscopy using barium sulfate as an internal standard. Barium sulfate was selected as the standard as its Raman spectrum does not overlap with that of silicon and its scattering cross-section is significantly lower. This allowed silicon admixed with barium sulfate in ratios as low as 0.00003 to be detected. The laser beam was defocussed to cover the sample area. 128 scans at 4 cm(-1) resolution with 600 mW of power at the sample achieved a detection limit of 0.1 mug of silicon in a 5 mg sample. Silicon to BaSO(4) ratios in the range 0.00003-0.06 showed a near linear response with any decade change being linear. The RSD for this analytical method was +/-2%. Silica fume and respirable silica dust showed silicon concentrations to be in the range 2.6-51.5 ppm and 0.05-0.7 mg m(-3) respectively.     

Quantitative analysis of topical gels and ointments by FT-Raman spectroscopy

A method for quantitative determination of ibuprofen (IBU), naproxen (NAP), methyl salicylate (MES) and menthol (MNT) in commercial topical gels and ointments using partial least squares (PLS) models based on FT-Raman spectra is described. The calculated relative standard errors of prediction (RSEP) were found to be in the range of 2.1–3.2% for the calibration and validation data sets. Two commercial topical gels containing 5.0% of IBU and 10% of NAP (w/w), as well as one ointment containing 15% of MES and 10% of MNT (w/w) as active pharmaceutical ingredients (APIs), were successfully quantified using the developed models with recoveries in the 99.2–101.5% range. The proposed procedure can be used as a fast, reliable and economic method for the quantification of APIs in topical gels and ointments.     

Identification of archaeological ivories using FT-Raman spectroscopy

FT-Raman spectroscopy has been used successfully for the non-destructive identification of modern ivories and is evaluated here for the identification of osseous materials from archaeological sites. Results on archaeological ivories are reported and the problems faced in matching FT-Raman spectra to standards for the validation of these materials are highlighted. Archaeological specimens of different dates, provenance and taphonomic history, including both conserved and unconserved items, have been analysed.     

The effects of stretching on wool fibres as monitored by FT-Raman spectroscopy

FT-Raman spectroscopy coupled with amide I band deconvolution was used to monitor the conformational changes of the peptide backbone of sulphite pre-treated wool fibres during stretching. The spectral changes observed are consistent with the transition of -helical to β-pleated sheet structure. These changes, which are most rapid during the early stages of stretching, can be related to protein secondary structure at both the crystalline and molecular levels. Analysis of the amide III region of the spectra reveals that a very small amount of additional disorder is imparted to the peptide backbone as a result of stretching. The consistency in the widths at half-height of the amide I band components implies that stretching does not significantly change the distribution of peptide chain conformations. From the Raman analysis of cells isolated from the stretched fibres, it is evident that conformational changes occur in both the cuticle and cortex. The most evident change, however, is in the cortical cells.     

Differentiation of solvated spironolactone samples by FT-Raman and FT-IR diffuse reflectance spectroscopy

Summary Five solvates of spironolactone were prepared by crystallization from absolute methanol, acetonitrile, absolute ethanol, ethyl acetate, and benzene, and characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and by FT-Raman spectroscopy. Of these solvates, all were found to be monosolvated except that formed with acetonitrile which gave a spironolactone-acetonitrile (2:1) complex as determined by elemental microanalysis. Distinctive IR and Raman spectral features of the solvates are discussed. Remarkable similarity is seen in the Raman spectra (1800–400 cm^–1) of the solvates obtained from methanol, ethanol, and ethyl acetate. The Raman spectrum of the benzene solvate is particularly useful for showing the presence of benzene because of the very intense band near 1000 cm^–1 which is unique to the Raman effect.Presented at the 36th Canadian Spectroscopy Conference, 1–3 August 1990, at Brock University, St. Catharines, ON, Canada     

Electron beam curing of methacrylated gelatin studied by EPR and FT-Raman spectroscopy

Gelatin was modified with glycidyl methacrylate. The methacrylated gelatins were cross-linked by electron irradiation. The cross-linking process was studied by FT-Raman and EPR spectroscopy.     

Quantitative determination of acetylsalicylic acid and acetaminophen in tablets by FT-Raman spectroscopy

A procedure for quantitative determination of acetylsalicylic acid and acetaminophen in pharmaceuticals by PLS (partial least squares) and PCR (principal component regression) treatment of FT (Fourier transform)-Raman spectroscopic data is proposed. The proposed method was tested on powdered samples. Three chemometric models were built: the first, for samples consisting of an active substance diluted by lactose, starch and talc; the second, in which a simple inorganic salt was applied as an internal standard and additions were not taken into account; and the third, in which a model was constructed for a commercial pharmaceutical, where all constituents of the tablet were known. By utilising selected spectral ranges and by changing the chemometric conditions it is possible to carry out fast and precise analysis of the active component content in medicines on the basis of the simplified chemometric models. The proposed method was tested on five commercial tablets. The results were compared with data obtained by intensity ratio and pharmacopoeial methods. To appraise the quality of the models, the relative standard error of predictions (RSEPs) were calculated for calibration and prediction data sets. These were 0.7-2.0% and 0.8-2.3%, respectively, for the different PLS models. Application of these models to the Raman spectra of commercial tablets containing acetylsalicylic acid gave RSEP values of 1.3-2.0% and a mean accuracy of 1.2-1.7% with a standard deviation of 0.6-1.2%.     

Routine FT-Raman spectroscopy with modified standard FT-IR instrument

A commercial FT-IR spectrometer (BRUKER IFS 66) was combined with a Raman module, having an NdYAG laser as source, a sample compartment, a filter for elimination of the exciting line from the spectrum and a detector. The interferometer and computer of the IFS 66 was used to record Raman spectra of small amounts of liquids and solids using a spherical sapphire sample cell.     

Characterization of the surface properties of xylan by FT-Raman spectroscopy and wicking technique

Using FT-Raman spectroscopy, column wicking technique and the equations of Washburn as well as van Oss et al., the surface properties of xylan, the main component in hemicelluloses, has been characterized and estimated. Raman spectrum showed that xylan has been structured by acetyl group and methyl-bonded glucurono group. Obtained results show that the surface free energy of xylan is higher in comparison with literature reported values for cellulose because the former has a larger Lifshitz–van der Waals component than the latter. However, xylan has been found to have very smaller polarity and orientation data than that of cellulose.     

FT-Raman spectroscopy of the reaction of polybutadiene with mercapto-thiadiazoles

Mercapto-thiadiazoles having potential anti-wear behaviour are reacted with polymers with existing viscosity index-improving properties in order to produce materials which may find a use as multifunctional lubricant additives. 2,5-Dimercapto-1,3,4-thiadiazole, 2-amino-5-mercapto-1,3,4-thiadiazole and 2-methyl-5-mercapto-1,3,4-thiadiadiazole were reacted with low MW polybutadiene containing vinyl-1,2, cis-1,4 and trans-1,4 (C=C) groups. The reactions were monitored using FT-Raman spectroscopy in order to determine quantitatively the consumption of the individual structural units when reacted with thiadiazoles. 2,5-Dimercapto-1,3,4-thiadiazole reacted readily with the polybutadiene, achieving 80% reaction within a few hours. The thiadiazole reacted selectively with the order of addition being cis>vinyl>trans. 2-Amino-5-mercapto-1,3,4-thiadiazole and 2-methyl-5-mercapto-1,3,4-thiadiazole were found to react more slowly and hence to a lesser extent (40 and 25%, respectively) over a similar time scale.     

Characterization of the surface properties of persimmon leaves by FT-Raman spectroscopy and wicking technique

To fit the request of developing new biomaterials using persimmon leaves as raw material, this paper reported the surface free energy and related components, e.g. the Lifshitz-van der Waals and Lewis acid-base components for persimmon leaves estimated by means of the column wicking technique. Considering this natural material might be varied of its properties with growing area, a characterization of it was initially performed by applying the FT-Raman spectroscopy. Based on the determined results, persimmon leaves have greater surface free energy, gammaS, than cellulose though it has been found rich in this component, e.g. of about 68.28%. Moreover, it was further observed that the persimmon leaves have great Lewis acid-base interactions component, gammaS(AB), contributed by the Lewis acid component, gammaS+. This suggests that the persimmon leaves are available to convert to new biomaterials expected forms.     

Thermotropic phase behaviour of sodium oleate as studied by FT-Raman spectroscopy and X-ray diffraction

The thermotropic behaviour of sodium oleate (NaOl) has been studied in the temperature range 10–125°C by using Fourier transform-Raman spectroscopy, X-ray diffraction and differential scanning calorimetry (DSC). The temperature dependence of conformationally sensitive bands in the CH₂ stretching (2800–2900 cm⁻¹), C–C stretching (1050–1150 cm⁻¹) and CH₃ rocking region (830–900 cm⁻¹) has been used to characterize the order/disorder behaviour of alkyl chains. It is found that in phase I, NaOl exhibits the crystalline ordered lamellar structure with a repeat period of 4.51 nm. The first broad peak in the DSC trace is due to superposition of two transitions (phase I to phase II and phase II to phase III), therefore, it is not possible to determine the lamellar structure of phase II. This broad transition from phase I to phase III is associated with the melting of methyl-sided chains and increase in gauche conformers in carboxylate-sided chains. Finally, NaOl undergoes a transition from crystalline to a liquid crystalline phase IV, which is associated with the melting of the carboxylate-sided chain.     

In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.     

Application of FT-Raman spectroscopy for the characterisation of new functionalised macromers

Fourier transform (FT)-Raman spectroscopy has been used extensively for the characterisation of polymers, especially polymers containing functional groups. New macromers with unsaturation have been synthesised using a living anionic polymerisation process. The reactions of living polystyryllithium with butadiene, followed by the capping reaction with mono or tri-functional chlorosilane norbornene were investigated. Characterisations by NMR and GPC have confirmed the formation of these macromers, but FT-Raman spectroscopy has revealed interesting information related to the isomerisation of the butadiene spacer in the polymer backbone.     

Monitoring the kappa number of bleached pulps based on FT-Raman spectroscopy

Cellulose - A new strategy was proposed to determine the Kappa number of bleached Eucalyptus globulus kraft pulps based on FT-Raman spectroscopy. Before modeling, smoothing (Savitzky-Golay),...     

A study of amber and copal samples using FT-Raman spectroscopy.

FT-Raman spectra were collected from fossil resins originating from a variety of geographical locations. The spectral profiles of most of the fossil resins could be related to modern resins containing diterpenoid components with predominantly labdane skeletons. The spectra collected from the fossil resin sample from Borneo differed from other fossil resins and was found to contain triterpenoid components. The differences in the spectral profile of fossil resins containing diterpenoid components are shown to relate to differences in level of maturation rather than geographical origin. FT-Raman spectra of fossil resins cannot be used to distinguish source although the degree of maturation can be used as an indicator to narrow the range of possible geographical origins.     

A study of binary adsorption of aromatics in completely siliceous zeolite ZSM-5 by FT-Raman spectroscopy

In the present work, binary adsorption of p-xylene and toluene in completely siliceous zeolite ZSM-5 was examined by FT-Raman spectroscopy in combination with powder X-ray diffraction. The results indicate that at total loadings of < or = 4 molecules per unit cell (u.c.) both p-xylene and toluene molecules prefer to reside at the intersections of straight and zigzag channels. The structure of the sorbate/sorbent complexes likely belongs to orthorhombic. At high loadings of 7 and 8 molecules/u.c., the framework of the zeolite transforms to another orthorhombic phase. In this high-loaded phase, toluene molecules are distributed evenly in both the channel intersection and the midsection of straight channel. Although p-xylene has access to both the channel intersection and the zigzag channel, it does show a slight preference for the channel intersection. The adsorptive behavior of these aromatics at intermediate total loadings of 5 and 6 molecules/u.c. is more complicated because the zeolitic framework is a mixture of two different orthorhombic phases.     

Laser-induced fluorescence and FT-Raman spectroscopy for characterizing patinas on stone substrates

This article reports on a compositional investigation of stone patinas: thin colored layers applied for protective and/or aesthetic purposes on architectural or sculptural substrates of cultural heritage. The analysis and classification of patinas provide important information of historic and artistic interest, as their composition reflects local practices, the availabilities of different materials, and the development of technological knowledge during specific historical periods. Model patinas fabricated according to traditional procedures and applied onto limestone, and a historic patina sample from the main façade of the San Blas Monastery in Lerma (a village in the province of Burgos, Spain), were analyzed by laser-induced fluorescence and Fourier transform Raman spectroscopy. The results obtained demonstrate the ability of these two analytical techniques to identify the key components of each formulation and those of the reaction products which result from the chemical and mineralogical transformations that occur during aging, as well as to provide information that can aid the classification of different types of patinas.

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Figure Cross section of model patina (left) and FT-Raman spectrum of historic patina from the façade of San Blas Monastery, Lerma, Burgos, Spain (right).