Determination of caffeine in solid pharmaceutical samples by FTIR spectroscopy

Fourier transform infrared spectroscopy has been used for the quantitative determination of caffeine in several pharmaceutical products: acetyl salicylic acid, paracetamol and propyphenazone. The method is simple, rapid and selective, and allows the determination of caffeine without sample pretreatment and without separation from the matrix. Two techniques for measuring the infrared spectra of caffeine are described: transmission through pellets and diffuse reflectance from powder (DRIFT). In both methods, samples were diluted (1%) with KBr. Caffeine in pharmaceutical matrices was recovered within 5% error in pellets and 10% by DRIFT. Relative standard deviations were generally 1.5% for repeated measurements on a single pellet and 5% for measurements on different pellets. DRIFT in the vacuum mode gave rather large RSDs. The limit of detection of the pellet technique was about 0.5% caffeine in the original sample.     

Predicting digestibility of ammonia fiber explosion (AFEX)-treated rice straw

The enzymatic digestibility of ammonia fiber explosion (AFEX)-treated rice straw was modeled by statistically correlating the variability of samples to differences in treatment using several different analytical techniques. Lignin content and crystallinity index of cellulose affect enzymatic hydrolysis the most. X-ray diffraction was used to measure the crystallinity index (CrI), while fluorescence and diffuse reflectance infrared (DRIFT) spectroscopy measured the lignin content of the samples. Multivariate analysis was applied to correlate the enzymatic hydrolysis results of the various samples with X-ray diffraction and spectroscopic data. Principal component analysis (PCA) and multilinear regression (MLR) techniques did not accurately predict the digestibility of the rice straw samples. The best correlation (R value of 0.775) was found between the treatment conditions of the AFEX process and the concentration of xylose at 24 h after enzymatic hydrolysis.     

A comparative study of mid-infrared diffuse reflection (DR) and attenuated total reflection (ATR) spectroscopy for the detection of fungal infection on RWA2-corn

An investigation into the rapid detection of mycotoxin-producing fungi on corn by two mid-infrared spectroscopic techniques was undertaken. Corn samples from a single genotype (RWA2, blanks, and contaminated with Fusarium graminearum) were ground, sieved and, after appropriate sample preparation, subjected to mid-infrared spectroscopy using two different accessories (diffuse reflection and attenuated total reflection). The measured spectra were evaluated with principal component analysis (PCA) and the blank and contaminated samples were classified by cluster analysis. Reference data for fungal metabolites were obtained with conventional methods. After extraction and clean-up, each sample was analyzed for the toxin deoxynivalenol (DON) by gas chromatography with electron capture detection (GC-ECD) and ergosterol (a parameter for the total fungal biomass) by high-performance liquid chromatography with diode array detection (HPLC-DAD). The concentration ranges for contaminated samples were 880–3600 g/kg for ergosterol and 300–2600 g/kg for DON. Classification efficiency was 100% for ATR spectra. DR spectra did not show as obvious a clustering of contaminated and blank samples. Results and trends were also observed in single spectra plots. Quantification using a PLS1 regression algorithm showed good correlation with DON reference data, but a rather high standard error of prediction (SEP) with 600 g/kg (DR) and 490 g/kg (ATR), respectively, for ergosterol. Comparing measurement procedures and results showed advantages for the ATR technique, mainly owing to its ease of use and the easier interpretation of results that were better with respect to classification and quantification.     

Direct analysis of thin-layer chromatographic spots of narcotics by means of diffuse reflectance Fourier transform infrared spectroscopy

The technique of diffuse reflectance Fourier transform infrared spectrometry (DRIFT) as an in situ detection method was used for the qualitative and quantitative analysis of drugs (heroin, cocaine and codeine) separated by thin layer chromatography.It was found that at a given interferometer throughput and detector sensitivity the quality of the spectrum depends strongly in the type of the chromatographic thin layer used. A detection limit of approx. 2 g was attained on a microcrystalline cellulose thin layer with a dynamically aligned Bio-Rad Digilab FTS 60A/896 type interferometer and room temperature DTGS detector. A reliable qualitative analysis can be made with as little as 10 to 15 g drug per spot.     

Variations in the chemical composition within pine (Pinus sylvestris) trunks determined by diffuse reflectance infrared spectroscopy and chemometrics

The feasibility of using DRIFT (diffuse reflectance infrared Fourier transform) spectroscopy combined with a multivariate analysis method (a PLS (projection to latent structures), regression) for predicting the distribution of the main organic constituents (cellulose, glucomannan, xylan, lignin, and extractives) within the Scots pine (Pinus sylvestris) stemwood was examined. PLS calibrations were carried out to establish a mathematical correlation between the data sets of conventional (“wet-chemistry-based”) wood analysis and the DRIFT spectra of the corresponding wood samples. Based on this approach, different surface maps on variations in the content of the main organic constituents within the stemwood matrix were shown.     

Specific Sorption Sites for Nitrogen in Zeolites NaLSX and LiLSX

Specific sorption sites for nitrogen, N₂, in NaLSX and LiLSX zeolites were investigated using a DRIFT spectroscopic method. Sorption of molecular hydrogen, H₂, by NaLSX or LiLSX zeolite at 77 K with DRIFT control of perturbation of sorbed molecules allowed to discriminate two or three different types of specific sorption sites in the respective zeolites. Their H–H stretching frequencies are 4077 and 4081 cm^–1 for NaLSX, and 4061, 4084 and 4129 cm^–1 for LiLSX. With reference to an independent investigation by methods of both sorption thermodynamics and molecular modeling for N₂ sorption on LiLSX, the first two of the corresponding bands were ascribed to H₂ sorption on lithium cations, Li⁺, localized in supercages of the faujasite, FAU, zeolite framework at sites SIII and SIII, while the latter band most likely belongs to H₂ sorption on Li⁺ cations at sites SII, and on hydroxyl groups, OH. Sorption of N₂ by Li⁺ cations at sites SIII and SIII is the strongest, resulting in a decrease of intensity of the corresponding DRIFT bands that stem from subsequent H₂ sorption. Nitrogen sorption by Li⁺ cations at sites SII is much weaker. Sorption of N₂ on Na⁺ cations at sites SIII in NaLSX zeolite is also stronger than by Na⁺ cations at sites SII.     

The effect of silane concentration on the adsorption of poly(vinyl acetate-co-maleate) and γ -methacryloxypropyl- trimethoxysilane onto E-glass fibers

The adsorption of a poly(vinyl acetate-co-maleate) (PVAM) emulsion onto E-glass fibers was investigated along with sizing formulations prepared by mixing the PVAM with varying concentrations of -methacryloxypropyltrimethoxysilane (MPS). The sized E-glass fibers were then characterized using Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Loss on Ignition (LOI) along with the DRIFT spectra indicated that the addition of silane to the PVAM emulsion caused a decrease in the amount of size on the fiber. The decrease in amount of size on the E-glass fibers did not coincide with a decrease in surface coverage, instead the XPS results indicated surface coverage had increased with silane addition. These results showed that small increases in the silane concentration appear to affect the amount of size adsorbed to the E-glass fibers     

Surface fine structure of hydrodesulfurization catalysts. New aspects of promoting effects of Co and Ni

By using the highpressure DRIFT, EXAFS, and TPDDRIFT methods, it is shown that the wellknown effects concerning Co–Mo/Al₂O₃ (i.e., promoting effect of Co or Ni, activating effect of catalyst presulfiding, and inhibiting effect of H₂S) are closely connected to each other. Some direct evidence of the interactions between Mo and Co on sulfided Co–Mo/Al₂O₃ is also shown.     

Thermal analysis (TG-DTA) and drift spectroscopy applied to investigate the evolution of humic acids in forest soil at different vegetation stages

Humic acids (HAs) extracted from soils developed under two Norwegian spruce (Picea abies, (L.) Karst) subalpine forests of northern Italy were characterized using chemical, thermal (TG-DTA) and spectroscopic (DRIFT) analyses. The samples were taken from five sites which differed in orientation (northern and southern exposure) and vegetal cover at different old age: grassland, regeneration, immature and mature stands. In general, the thermal patterns of HAs were similar (three exothermic reactions appeared around at 300, 400 and 500°C) in both sites in grasslands and regeneration while a considerable modification appeared in HA from stands of different age at northern and southern exposure site. DRIFT spectroscopy confirmed the differences observed through TG-DTA analysis. In particular the main structural changes were ascribed to modification of carbonyl group and of CH stretching in aliphatic components in each HAs from different sites.     

Sodium stearate adsorption onto titania pigment

The interaction of sodium stearate with titania pigment particles from aqueous suspension has been investigated using thermal analysis and infrared spectroscopy combined with electrochemical studies. Thermogravimetric analysis (TGA) was used both to determine the adsorption isotherm and to investigate the interaction behavior. Monolayer coverage is determined to be 0.95 mg/m(2); however, unlike the case with organic solvents, multilayer adsorption occurs. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, combined with TGA, revealed that the surface monolayer is chemically bound. DRIFT spectroscopic data also indicated that the stearate bridged across two aluminum atoms. Subsequent stearate layers were physisorbed to the stearate monolayer and were readily removed with acetone washing.     

In situ high-throughput study of drug polymorphism under controlled temperature and humidity using FT-IR spectroscopic imaging

Fourier transform infrared (FT-IR) spectroscopic imaging in combination with a controlled humidity cell was applied to simultaneously monitor crystallisation of several binary mixtures of two drugs under identical environment. The effect of relative humidity was studied on samples of binary mixtures of nifedipine and nitrendipine with different molar ratios as well as on amorphous nitrendipine. All samples were arranged in array format on the surface of BaF₂ window for simultaneous imaging using an infrared focal plane array detector. The effect of sample thickness on the analysis of imaging results was addressed using novel approach to create images. The thickness-independent images have been obtained by plotting the distribution of the wavenumber corresponding to the peak maximum of the ν(NH) vibrational mode which is sensitive to the formation of the various crystalline polymorphs. The FT-IR spectroscopic imaging approach described in this work can be utilised in further high-throughput studies of many samples under controlled environment.     

Surface characterization of functional poly(diacetylene) and poly(butadiene) mono- and multilayers

The surface properties of Langmuir-Blodgett mono- and multilayers of a variety of amphiphilic poly(diacetylene)s and poly(butadiene)s were investigated by contact angle, streaming potential, ellipsometry, and X-ray photoelectron spectroscopic (XPS) measurements. Captive air and octane angles varied between approximately 60° and 105° for hydrophobicx-layers and 31° to 46° for hydrophilic surfaces depending on the particular head group, whereas advancing angles determined via the vertical plate method are considerably higher. Negative streaming potentials were obtained for all surfaces. Positively charged monolayers yielded less negative- potential values (–28 mV) than negatively charged (–52 mV) or hydrophobic (–50 mV) layers. Ellipsometry measurements yielded an average layer thickness of 27±6 Å for 3 to 11 layers. X-ray photoelectron spectroscopy results qualitatively confirmed the expected composition. All of the samples, which were handled and stored in air after deposition and polymerization, were surface oxidized.Dedicated to Prof. Dr. F. H. Müller.     

Synthesis and structures of oligothioarylenecyclophosphonites

A new representative of phospho(scIII)crown ethers was obtained based on 4,4-thiodiphenol and tetraethyldiamide of phenylphosphonous acid. Thiaphospho(III)crown ethers can be prepared by different methods depending on the ratio of the initial reactants and the reaction conditions. The structures of the compounds obtained were confirmed by spectroscopic data and X-ray structural analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2313–2315, September, 1996.     

Quantitative analysis of functional groups in HDPE powder by DRIFT spectroscopy

FT-IR spectra of ethylene homopolymers and ethylene/1-hexene copolymers polymerized under different conditions were studied by transmission and diffuse reflection (DRIFT) spectroscopy. The absorbance spectra of film samples were compared with the DRIFT spectra of powders ground from the films. For determining the concentration of the methyl and unsaturated (vinyl, vinylidene and trans-vinylene) groups of polyethylene powders the DRIFT spectra were calibrated by comparing the IR intensities of the corresponding bands measured by the two methods. The results proved that the effect of differences in scattering of the polymer powder originating from the irregularity of the top surface, as well as the size and shape of the particles can be eliminated by the use of a proper internal standard. Linear correlation was established between the logarithms of the normalized intensities measured in absorbance and Kubelka-Munk units. In the case of polyethylene the selection of the internal reference band affects significantly the accuracy of the calibration due to the difference in the refractive indices of the crystalline and amorphous phases.     

A Markov random field based approach to the identification of meat and bone meal in feed by near-infrared spectroscopic imaging

Contaminated meat and bone meal (MBM) in animal feedstuff has been the source of bovine spongiform encephalopathy (BSE) disease in cattle, leading to a ban in its use, so methods for its detection are essential. In this study, five pure feed and five pure MBM samples were used to prepare two sets of sample arrangements: set A for investigating the discrimination of individual feed/MBM particles and set B for larger numbers of overlapping particles. The two sets were used to test a Markov random field (MRF)-based approach. A Fourier transform infrared (FT-IR) imaging system was used for data acquisition. The spatial resolution of the near-infrared (NIR) spectroscopic image was 25 μm?×?25 μm. Each spectrum was the average of 16 scans across the wavenumber range 7,000-4,000 cm^?1, at intervals of 8 cm^?1. This study introduces an innovative approach to analyzing NIR spectroscopic images: an MRF-based approach has been developed using the iterated conditional mode (ICM) algorithm, integrating initial labeling-derived results from support vector machine discriminant analysis (SVMDA) and observation data derived from the results of principal component analysis (PCA). The results showed that MBM covered by feed could be successfully recognized with an overall accuracy of 86.59 % and a Kappa coefficient of 0.68. Compared with conventional methods, the MRF-based approach is capable of extracting spectral information combined with spatial information from NIR spectroscopic images. This new approach enhances the identification of MBM using NIR spectroscopic imaging.

Determination of uranium and thorium concentration in some Egyptian rock samples

Uranium (U) and thorium (Th) isotopes and their several radioactive descendants found in soil, rock, water, plants, air, etc., contribute to the natural radiation exposure of the population. Phosphate rocks are really rich natural sources of uranium and thorium among the other minerals forming the earth's crust. U and Th concentrations in some Egyptian phosphate samples were determined using a nuclear track registration methodology and -ray spectroscopy. The resulting latent tracks from all -decaying isotopes in both U and Th series were recorded in plastic detectors. A uniquely sensitive polycarbonate CR-39 nuclear detector was used. Results showed that the U and Th concentration in the samples studied range from about 4.0 up to 35.0 ppm and from 11.0 to 124.0 ppm, respectively. Results are discussed within the frame work of track formation methodology in plastic and -ray spectroscopic analysis.     

Comparison between thermal analysis and mass spectroscopic studies of uranyl oxinates

The 5,7-dichloro, 5,7-dibromo, 5,7-diiodo and 5,6-dinitro derivatives of oxine (ligandsL ₁,–L ₄) were used to prepare uranyl chelates (A ₁–A ₄). Thermal analysis (DTA) and mass spectroscopic studies were performed. The stoichiometries of the chelates were determined by elemental analysis, molecular weight determination applying an -spectroscopic liquid scintillation counter and mass spectral measurements. The uranylligand ratios were found to be 11 for A₁, 13 for A₂, 12 (monohydrate) for A₃, and 12 forA ₄. The correlation between the thermal analysis and mass spectra was examined. The activation energy required for each step of thermal degradation of the ligands and chelates was calculated. The natures of most of the molecular ions obtained in the mass spectra were also explained.     

Physicochemical and Catalytic Properties of La1 – xCaxFeO3 – 0.5x Perovskites Prepared Using Mechanochemical Activation

The phase composition of La_{1 – x} Ca _x FeO_{3 – 0.5x} perovskites synthesized from preactivated oxides was studied by powder X-ray diffraction analysis and differential dissolution. The system does not form a continuous series of homogeneous solid solutions. No intermediate samples from this series are monophasic. It was found that the synthesis under nonequilibrium conditions (mechanical activation + calcination at 900° for 4 h) resulted in nonequilibrium microheterogeneous solid solutions with degrees of calcium substitution for lanthanum of no higher than 0.5. A longer calcination (for 16 h) or an increase in the calcination temperature of solutions up to 1100 ° decreased the calcium content of the samples down to x 0.2 because of the formation of a brownmillerite phase. The catalytic activity of the test samples in the oxidation of CO changed nonmonotonically with x, and it was maximum at x = 0.5–0.6, which correlates with the maximum density of interphase boundaries in these samples.     

Rapid speciation of Se(IV) and Se(VI) by flow injection–capillary electrophoresis system with contactless conductivity detection

A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM l-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 g L^–1 and 7.5 g L^–1 for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations.