Backscatter Mode Research Articles

Quantitative Transmission Raman Spectroscopy of Pharmaceutical Tablets and Capsules

Quantitative analysis of pharmaceutical formulations using the new approach of transmission Raman spectroscopy has been investigated. For comparison, measurements were also made in conventional backscatter mode. The experimental setup consisted of a Raman probe-based spectrometer with 785 nm excitation for measurements in backscatter mode. In transmission mode the same system was used to detect the Raman scattered light, while an external diode laser of the same type was used as excitation source. Quantitative partial least squares models were developed for both measurement modes. The results for tablets show that the prediction error for an independent test set was lower for the transmission measurements with a relative root mean square error of about 2.2% as compared with 2.9% for the backscatter mode. Furthermore, the models were simpler in the transmission case, for which only a single partial least squares (PLS) component was required to explain the variation. The main reason for the improvement using the transmission mode is a more representative sampling of the tablets compared with the backscatter mode. Capsules containing mixtures of pharmaceutical powders were also assessed by transmission only. The quantitative results for the capsules' contents were good, with a prediction error of 3.6% w/w for an independent test set. The advantage of transmission Raman over backscatter Raman spectroscopy has been demonstrated for quantitative analysis of pharmaceutical formulations, and the prospects for reliable, lean calibrations for pharmaceutical analysis is discussed.

A non-invasive in vitro technique for the three-dimensional quantification of microdamage in trabecular bone

An accurate analysis and quantification of microdamage is critical to understand how microdamage affects the mechanics and biology of bone fragility. In this study we demonstrate the development and validation of a novel in vitro micro-computed tomography (microCT) method that employs lead–uranyl acetate as a radio-opaque contrast agent for automated quantification of microdamage in trabecular bone. Human trabecular bone cores were extracted from the femoral neck, scanned via microCT, loaded in unconfined compression to a range of apparent strains (0.5% to 2.25%), stained in lead–uranyl acetate, and subsequently re-scanned via microCT. An investigation of the regions containing microdamage using the backscatter mode of a scanning electron microscope (BSEM) showed that the lead–uranyl sulfide complex was an effective contrast agent for microdamage in bone. Damaged volume fraction (DV/BV), as determined by microCT, increased exponentially with respect to applied strains and proportionately to mechanically determined modulus reduction ( p < 0.001). Furthermore, the formation of microdamage was observed to occur before any apparent stiffness loss, suggesting that the localized tissue yielding occurs prior to the structural yielding of trabecular bone. This non-invasive in vitro technique for the detection of microdamage using microCT may serve as a valuable complement to existing morphometric analyses of bone.

Multiwall carbon nanotube/epoxy composites produced by a masterbatch process

A masterbatch process based on a minicalander (three-roller mill) and a vacuum dissolver was developed in order to produce multiwall carbon nanotube/epoxy composites with loading fractions of 0.5, 1.0, and 2.0 wt.%. TEM and SEM analyses were performed to investigate the dispersion results. A contrast imaging in the SEM backscattering mode revealed a homogeneous distribution of carbon nanotubes in the whole volume of the material. Furthermore, an interesting correlation was found to exist between the network structure formed by the nanotubes in the epoxy matrix and the appearance of fracture surface of the nanocomposites. Furthermore, the nanocomposites exhibited an electrical conductivity in the regime of some 10−2 S/m.

New resonant backscattering mode in a small-size quantum interferometer

New resonant backscattering mode in a small-size quantum interferometer

Addition of cement to lime-based mortars: Effect on pore structure and vapor transport

The main focus of this work is to determine the effect of cement addition, a common practice in many restorations, on the pore structure of lime-based mortars. A second target is to establish correlations between microstructure and water vapor transport across the mortar, which is a key characteristic of building decay. In order to achieve these objectives, we prepared a set of mortars consisting of air-hardening lime with a progressively increasing cement content, as well as a mortar containing hydraulic lime. Several different techniques, most notably mercury intrusion porosimetry and scanning electron microscopy in the backscatter mode, were used to investigate the pore structure. The results from these procedures led to the conclusion that porosity and pore size are progressively reduced as cement content increases. Moreover, an excellent correlation between pore radius parameter and the vapor diffusion coefficient was established. Hydraulic lime mortar exhibited textural parameters and diffusivity values halfway between those of the different lime/cement mixes studied.

In-Situ SEM Observations of Moving Interfaces during Recrystallisation

To obtain further progress and a more detailed understanding of the mechanisms involved in recrystallisation, new and more accurate techniques such as in-situ observations are necessary. This innovative method has been used to monitor the recrystallisation process in a FEGSEM equipped with hot stage. Observations are done in backscatter mode with particular attention to orientation contrast. EBSD maps of the observed areas can be acquired before and after recrystallisation. Details of the movement of the interfaces between the recrystallised region and the parent structure are recorded and analysed. The results show that the grain boundaries observed do not move smoothly but with a jerky motion. The recrystallising front sweeps through small areas, corresponding to single sub-grains or small groups of them, very rapidly and then stops at other sub-grain boundaries for varying time before progressing to the following area.

New resonant backscattering mode in a small-size quantum interferometer

Giant conductance oscillations quasi-periodic in the gate voltage are observed in the open state of a small-size quantum interferometer (of effective radius r ≈ 100 nm) based on the high-mobility 2D electron gas of an AlGaAs/GaAs heterojunction. These oscillations presumably result from the multiparticle effects that occur in the interferometer arms and give rise to a strong backscattering and to conductance peaks, whose period corresponds to a one-electron change in the number of electrons in the arms.

Study of materials using Mössbauer spectroscopy

A comprehensive review is presented of the recent contributions Mössbauer spectroscopy has made in materials science and engineering. After a brief introduction to the basic methodology, examples of the application of 57Fe and 119Sn Mössbauer spectroscopy in both transmission and back-scattering mode are presented and discussed. Recent technological and software developments of this technique are also included. Coverage is further extended to recent, pertinent developments in space research and also in biological science and technology where Mössbauer techniques are very widely used. Efforts have also been made to cover applications to archaeological samples where Mössbauer spectroscopy is an important analytical tool.

Fabrication of Porous Nb2O5 by Plasma Electrolysis Anodization and Electrochemical Characterization of the Oxide

Porous electrodes were fabricated by applying anodic pulses of and duration to pure Nb in phosphate buffered saline solution (PBS), aiming at biomaterial applications. The porosity of the oxide could be controlled by the number of pulses. X-ray photoelectron spectroscopy analysis confirmed the oxide to be . The electrochemical behavior and interfacial properties of the porous were characterized in PBS by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). EIS measurements indicate that the oxide film has a two-layer structure with a compact inner layer and a porous outer layer, and the pores were sealed by precipitates during long-time aging in PBS. The two-layer structure of the oxide film was observed by examination of the cross section using scanning electron microscopy in backscatter mode. The CV measurements reveal that the oxide exhibits an electrochemical “rectifying” property. It is stable over a wide potential range but shows hydrogen uptake upon cathodic polarization below vs .

Resolution of fine fibrous C-S-H in backscatter SEM examination

Secondary electron mode SEM images of hardened cement paste (obtained on fracture surfaces) have been published since the early 1970s. Most such images emphasized fine fibrous or dendritic C-S-H structures, which are commonly found in porous areas preferentially exposed by fracturing. Such fibrous structures are not generally seen in backscatter-mode SEM images obtained on polished surfaces. Examination with a high-resolution field-emission SEM (FE-SEM) instrument in the backscatter mode resolves these fibrous C-S-H structures, and suggests that failure to image them in conventional backscatter SEM is primarily due to inadequate resolution.

Conceiving an Easy-to-Understand and Automated Polarimeter: Application to a Study of Collagen

In this paper, the authors describe the design and the experimentation of a polarimeter aimed at characterizing the properties of some scattering materials (e.g., a scattering liquid containing a foreign body, or skin components, such as collagen). The polarimeter presents the advantage of offering an easy understanding of Stokes and Mueller formalism. Thus, it is typically suited for university students in physics (Master's level), giving them a clear understanding of polarization and birefringence. Another application is possible in schools of engineering, where students may use their design abilities to improve the apparatus performance. Apparatus automation was performed as well, providing easier use for experiment (commodity of use, reproducibility, and possible multiplication of measurements). The apparatus was tested in transillumination and backscattering modes. More generally, measurements can be performed with angles varying from 0/spl deg/ to 150/spl deg/ between the propagation direction and the line from the sensor to the sample material. In addition, the sensor can be either a photodiode (results presented here) or a two-dimensional (2-D) sensor charge-coupled device (CCD) camera. As an application, the apparatus was used to differentiate irradiated and nonirradiated collagen.

Focus on Analytical Equipment

Focus on Analytical Equipment

The Human Bone–Oxidized Titanium Implant Interface: A Light Microscopic, Scanning Electron Microscopic, Back‐Scatter Scanning Electron Microscopic, and Energy‐Dispersive X‐Ray Study of Clinically Retrieved Dental Implants

Surface modification of titanium implants by anodic oxidation may lead to enhanced bone integration. For instance, in vivo studies have demonstrated formation of more bone contacts in less time than for turned control implants. In addition, oxidized implants have shown a higher resistance to torque forces, indicating a strong interlock between bone and the oxide layer. However, the structure of the oxidized titanium-bone interface in high resolution is not known. The aim of the study was to analyze the human bone-oxidized titanium interface at a high-resolution level. Of particular interest was the relationship between bone tissue and the pores of the surface oxide. Twelve clinically retrieved implants with an oxidized surface (TiUnite, Nobel Biocare AB, Göteborg, Sweden) were used. Seven were regular dental implants and five were experimental mini-implants and had been subjected to immediate, early, or no loading. They were retrieved after 5 to 9 months of healing and were processed and analyzed using light microscopy, scanning electron microscopy (SEM) in normal and back-scatter (BS-SEM) modes, and energy-dispersive x-ray (EDX) analysis techniques. Bone formation was observed to occur from adjacent bone structures toward the implant surface, and it was evident that bone formation had occurred at the implant surface. SEM, BS-SEM, and EDX revealed that mineralized bone had grown into the pores of the surface oxide layer, including pores with small diameters (< 2 microm). The clinically retrieved oxidized implants showed evidence of bone growth into the pores of the surface oxide layer. The findings indicate the establishment of a strong interlock between the bone and the oxidized titanium implant, which is suggested to be beneficial for clinical performance.

Photochemistry of 2-(2‘-Hydroxyphenyl)benzothiazole Encapsulated in Nanosized Zeolites

The in situ incorporation and characterization of 2-(2‘-hydroxyphenyl)benzothiazole (HBT) in the cages of nanosized FAU zeolites is reported. We demonstrate the advantage of using colloidal zeolite solutions to perform subpicosecond transient experiments on nanosized host/guest systems. FAU molecular sieve is prepared from precursor solutions containing as organic template only tetramethylammonium hydroxide (TMA) or both molecules HBT and TMA, using a hydrothermal treatment at 90 °C for 70 h. In situ dynamic light scattering investigations of the precursor solutions and the crystalline suspensions are performed with the original sample concentrations using a backscattering mode. The radius of the amorphous entities formed in the TMA-containing precursor solutions is about 25 nm, while that of the amorphous species in the HBT/TMA precursor solution is about 15 nm. The final particle size of FAU and HBT/FAU colloidal zeolites is 100 and 80 nm, respectively. The encapsulation of HBT with different concentrat...

The localization of occluded matrix proteins in calcareous spicules of sea urchin larvae

The sea urchin embryo forms calcareous endoskeletal spicules composed of calcite and an occluded protein matrix. Though the latter is approximately 0.1% of of the mass, the composite has substantially altered material properties, e.g., conchoidal fracture planes and increased hardness. Experiments were conducted to examine the localization of matrix proteins occluded in the mineral by use of immunocytochemistry coupled with scanning electron microscopy (SEM). The isolated, unfixed spicules were etched under relatively gentle conditions and exposed to affinity purified antibodies made against two different matrix proteins, as well as an antibody to the entire constellation of matrix proteins. Immunogold tagged secondary antibody was used to observe antibody localization in the back scatter mode of SEM. All proteins examined were very widely distributed throughout the calcite, supporting a model of the structure in which a multiprotein assemblage is woven with fine texture around microcrystalline domains of calcite. Gentle etching revealed a laminar arrangement of calcite solubility, consistent with a stepwise deposition of matrix and mineral to increase girth of the spicule.

Electron microprobe imaging for the characterization of polymer matrix composites

Traditionally, image analysis of polymer matrix composite (PMC) materials has been achieved through optical microscopy and, to a lesser extent, scanning electron microscopy. In this study, image analysis using an electron microprobe in backscatter mode is introduced as a method to provide a qualitative comparison of void content and fiber packing in PMC materials. Composite parts were fabricated using a vacuum-assisted resin transfer molding (VARTM) process and another process known as the composites pressure resin infusion system (ComPRIS). Voids were observed in the composite specimens fabricated by the VARTM process, where resin infusion is driven by vacuum. No significant voids were observed in the composite specimens fabricated by the ComPRIS process, where resin infusion is driven by pressure. The apparent difference in void content is attributed to the difference in the resin infusion driving force, i.e. vacuum versus pressure. Backscattered electron imaging of samples using an electron microprobe proved to be a suitable technique for imaging PMC surfaces.

Reaction products of densified silica fume agglomerates in concrete

Most silica fume currently used in concrete is in the dry densified form and consists of agglomerates of sizes between 10 μm and several millimeters. Many of these agglomerates may break down only partially in normal concrete mixing. Examination of various mature silica-fume-bearing concretes using backscatter mode scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis shows that such agglomerates have reacted in situ and given rise to recognizable types of reaction products filling the space within the original outline of the agglomerate. One type is “quiescent,” and usually shows no evidence of volume instability. EDX spectra indicate that the product formed within such grains is C-S-H of very low Ca/Si ratio, with modest alkali contents. Other silica fume agglomerates may undergo a distinct alkali–silica-type reaction (ASR), with the reaction product found within the original outline of the agglomerate having significantly less calcium and usually much higher alkali contents than the quiescent type. Such reacted agglomerates show evidence of local expansion, shrinkage cracking (on drying), and other features common to ASR. Both types may be found within the same concrete, sometimes in close proximity. It further appears that exposure to seawater may convert previously formed reaction products of silica fume agglomerates to magnesium silicate hydrates.

FT–Raman spectrometry determination of Malathion in pesticide formulations

A fast and environmentally friendly method has been developed for Fourier transform–Raman (FT–Raman) spectrometry determination of Malathion in pesticide emulsifiable concentrate formulations. The method is based on the measurement of intensity peak height values at 1737cm−1 Raman shift corrected using a baseline defined at 1900cm−1. Samples were diluted with CHCl3 and the FT–Raman spectra collected in back-scattering mode over 3.3min at a nominal resolution of 4cm−1 accumulating 50 scans per spectra and using a laser power of 1250mW. The developed procedure provided a limit of detection of 1.8% w/w in the original sample. Results found by FT–Raman spectrometry were statistically comparable with those obtained by flow injection Fourier transform infrared spectrometry, FIA–FTIR, and gas chromatography (GC) and were in good agreement with those reported by the manufacturer. The FT–Raman developed procedure reduces drastically the chlorinated solvent waste generation and avoids the contact of the operator with toxic products, being a fast alternative to the CIPAC recommended GC procedure.

Approximate analytical solution of the Takagi equations for X-ray diffraction in the backscattering mode from a cylindrically bent crystal

The dynamic diffraction of a spherical X-ray wave from a cylindrically bent crystal in the backscattering mode has been theoretically studied. An approximate analytical solution of the system of Takagi differential equations is obtained under certain conditions imposed on the coordinates of atoms inside the crystal.

Non-destructive and clean prediction of aviation fuel characteristics through Fourier transform-Raman spectroscopy and multivariate calibration

The combination of Fourier transform (FT)-Raman spectroscopy and partial least squares (PLS) regression is proposed to be used in off-line kerosene quality control. Here, six important physico-chemical properties have been studied: Abel flash point, initial boiling point (IBP), 10% of distilled sample, final boiling point (FBP), total percentage of aromatic compounds (% aromatics) and viscosity. The Raman spectra were obtained directly from standard 2 ml glass vials ( 12 mm×32 mm), using a Bruker RFS 100 FT-Raman spectrometer, equipped with a 1064 nm Nd:YAG laser and a Ge detector, in back-scattering mode and accumulating 25 scans (150 s acquisition time) with a laser power of 300 mW. All Raman spectra were unit normalized in order to avoid the influence of the laser power into the regression models. Different Raman shift spectral ranges have been evaluated, the 193.5–1688.1 cm −1 region being the most satisfactory one. Corrected standard errors of prediction of 1.9, 2.3, 2.8 °C, 0.19 cSt and 0.7% were obtained for flash point, IBP, FBP, viscosity and % aromatics, respectively. The influences of the glass vials, sample positioning and laser power have been studied, as well.