Showing papers in "Applied Spectroscopy in 1994"
TL;DR: In this article, acoustic tunable filters (AOTF) and liquid crystal tunable filter (LCTF) are evaluated for their suitability as fluorescence microscopy imaging spectrometers.
Abstract: Acousto-optic tunable filters (AOTF) and liquid crystal tunable filters (LCTF) are evaluated for their suitability as fluorescence microscopy imaging spectrometers. AOTFs are solid-state birefringent crystals that provide an electronically tunable spectral notch passband in response to an applied acoustic field. LCTFs also provide a notch passband that can be controlled by incorporating liquid crystal waveplate retarders within a Lyot birefringent filter. In this paper, spectroscopic performance and imaging quality are contrasted by evaluation of model systems. Studies include transmission imaging of standard resolution targets, multispectral fluorescence emission imaging of tagged polystyrene microspheres, and immunofluorescence imaging of neurotransmitters within rat-brainstem thin sections. In addition, the first use of LCTFs for Raman microscopy is demonstrated. Raman microscopy is a noninvasive spectral imaging technique that can provide chemically significant image contrast complementary to fluorescence microscopy without the use of stains or tags.
279 citations
TL;DR: A Fourier transform infrared spectroscopic method has been developed to analyze protein secondary structure by employing the amide III spectral region (1350-1200 cm-1).
Abstract: A Fourier transform infrared spectroscopic method has been developed to analyze protein secondary structure by employing the amide III spectral region (1350-1200 cm-1) Benefits of using the amide III region have been shown to be substantial The interference from the water vibration (~ 1640 cm-1) in the amide I region can be avoided when one is using the amide III band; furthermore, the amide III region also presents a more characterized spectral feature which provides easily resolved and better defined bands for quantitative analysis Estimates of secondary structure are accomplished with the use of Fourier self-deconvolution, second derivatization, and curve-fitting on original protein spectra The secondary structure frequency windows (α-helix, 1328-1289 cm-1; unordered, 1288-1256 cm-1; and β-sheets, 1255-1224 cm-1) have been obtained, and estimates of secondary structural contents are consistent with X-ray crystallography data for model proteins and parallel results obtained with the use of the amide I region We have further applied the analysis to the structural change of calsequestrin upon Ca2+ binding Treatment of calsequestrin with 1 mM Ca2+ results in the formation of crystalline aggregates accompanied by a 10% increase in α-helical structure, which is consistent with previous results obtained by Raman spectroscopy Thus the amide III region of protein IR spectra appears to be a valuable tool in estimating individual protein secondary structural contents
189 citations
TL;DR: In this paper, the authors demonstrate a different approach to set up a confocal Raman microscope using a stigmatic spectrograph and a CCD detector, which provides a depth resolution of ∼2 μm.
Abstract: Confocal Raman microspectroscopy has previously used pinholes placed at the back focal plane of the microscope to provide depth resolution along the optical axis. The process of optimizing the pinhole alignment can often be difficult and time-consuming. We demonstrate a different approach to setting up a confocal Raman microscope using a stigmatic spectrograph and a CCD detector. This arrangement is easy to use and provides a depth resolution of ∼2 μm.
156 citations
TL;DR: In this paper, a digital Fourier filter is combined with partial least squares regression to generate a calibration model for glucose that is insensitive to sample temperature, which is initially created by using spectra collected over the 5000 to 4000 cm-1 spectral range with samples maintained at 37°C.
Abstract: A digital Fourier filter is combined with partial least-squares (PLS) regression to generate a calibration model for glucose that is insensitive to sample temperature. This model is initially created by using spectra collected over the 5000 to 4000 cm-1 spectral range with samples maintained at 37°C. The analytical utility of the model is evaluated by judging the ability to determine glucose concentrations from a set of prediction spectra. Absorption spectra in this prediction set are obtained by ratioing single-beam spectra collected from solutions at temperatures ranging from 32 to 41°C to reference spectra collected at 37°C. The temperature sensitivity of the underlying water absorption bands creates large baseline variations in prediction spectra that are effectively eliminated by the Fourier filtering step. The best model provides a mean standard error of prediction across temperatures of 0.14 mM (2.52 mg/dL). The benefits of the Fourier filtering step are established, and critical experimental parameters, such as number of PLS factors, mean and standard deviation for the Gaussian shaped Fourier filter, and spectral range, are considered.
148 citations
TL;DR: An analytical multicomponent method for the blood substrates total protein, glucose, total cholesterol, triglycerides, and urea in human EDTA plasma by FT-IR spectroscopy is described in this paper.
Abstract: An analytical multicomponent method for the blood substrates total protein, glucose, total cholesterol, triglycerides, and urea in human EDTA plasma by FT-IR spectroscopy is described. The spectra were obtained with the use of the attenuated total reflection technique. Partial least-squares was applied for multivariate calibration over optimized spectral ranges. The mean-square prediction errors for the population of 126 plasma samples of different patients calculated by cross-validation are in the range of clinical acceptance. Within an error variance analysis, the contributions of the reference method and the spectrometric measurement to the average (root mean square) prediction error have been estimated for each substrate, giving evidence of the limitations of the spectrometric method. The problem of the biocompatibility of the plasma has been investigated, and the protein adsorption onto the ATR crystal can be reduced to a constant and tolerable level by appropriate cleaning and rinsing. The potential for further improvement is discussed.
129 citations
TL;DR: In this article, a nanosecond time-resolved infrared spectroscopic system based on a dispersive scanning spectrometer has been constructed, which is an advanced version of a similar system reported in a previous paper; the time resolution has been improved from 1 μs to 50 ns and the sensitivity from 10-4 in intensity changes to 10-6.
Abstract: A nanosecond time-resolved infrared spectroscopic system based on a dispersive scanning spectrometer has been constructed. This is an advanced version of a similar system reported in a previous paper; the time resolution has been improved from 1 μs to 50 ns and the sensitivity from 10-4 in intensity changes to 10-6. These have been achieved by the use of a high-temperature ceramic infrared light source, a photovoltaic MCT detector, and a low-noise, wide-band preamplifier developed specifically for the present purpose. Time-resolved infrared spectra of a few samples of photochemical and photobiological interests are presented to show the capability of the system. The origin of the thermal artifacts, which have been found to hamper the time-resolved infrared measurements seriously, is shown to be due to the transient reflectance change induced by a small temperature jump. The future prospect of time-resolved infrared spectroscopy is discussed with reference to other methods including infrared laser spectroscopy and Fourier transform infrared spectroscopy.
116 citations
TL;DR: In this paper, the use of an indium antimonide (InSb) multichannel imaging detector for near-infrared absorption spectroscopic microscopy is described.
Abstract: Near-infrared spectroscopy is a sensitive, noninvasive method for chemical analyses, and its integration with imaging technologies represents a potent tool for the study of a wide range of materials. In this communication the use of an indium antimonide (InSb) multichannel imaging detector for near-infrared absorption spectroscopic microscopy is described. In particular, a 128 × 128 pixel InSb staring array camera has been combined with a refractive optical microscope and an acousto-optic tunable filter (AOTF) to display chemically discriminative, spatially resolved, vibrational spectroscopic images of biological and polymeric systems. AOTFs are computer-controlled bandpass filters that provide high speed, random wavelength access, wide spectral coverage, and high spectral resolution. Although AOTFs inherently have a wide range of spectroscopic applications, we apply this technology to NIR absorption microscopy between 1 and 2.5 μm. The spectral interval is well matched to the optical characteristics of both the NIR refractive microscope and the AOTF, thereby providing near-diffraction-limited performance with a practical spatial resolution of 1 to 2 μm. Design principles of this novel instrumentation and representative applications of the technique are presented for various model systems.
112 citations
TL;DR: In this paper, the lifetime of a series of crude oils at various concentrations have been measured for UV-visible excitation and emission wavelengths, and the lifetime results are compared with fluorescence spectra and quantum yields for these solutions.
Abstract: The fluorescence lifetimes of a series of crude oils at various concentrations have been measured for UV-visible excitation and emission wavelengths. The lifetime results are compared with fluorescence spectra and quantum yields for these solutions. The concentration effects of energy transfer and quenching are large and result in a significant decrease in fluorescence lifetimes for high concentrations and for heavy crude oils. Thus, radiationless processes dominate in energy transfer. At high concentrations, energy transfer produces large red shifts in fluorescence emission spectra, while quenching produces a large reduction in quantum yields. Stern-Volmer analyses of lifetime and quenching data show a linear dependence of energy transfer and quenching rates on concentration. The rate constants are consistent with collisions which are very efficient at energy transfer and quenching, and the rates of these two processes are comparable.
111 citations
TL;DR: In this article, a near-infrared surface-enhanced Raman scattering (NIR SERS) was detected with high sensitivity for two model compounds, crystal violet and the DNA base adenine, adsorbed on silver and gold colloidal particles in aqueous solutions.
Abstract: Near-infrared surface-enhanced Raman scattering (NIR SERS) was detected with high sensitivity for two model compounds, crystal violet and the DNA base adenine, adsorbed on silver and gold colloidal particles in aqueous solutions. The NIR SERS spectra were measured with a fiber-optic probe with the use of a Ti:sapphire laser at 850 nm as the excitation source and a charge-coupled device (CCD) as the detection system. In a step to achieve the optimal electromagnetic SERS-enhancement conditions, silver and gold sols were modified to shift their extinction spectra more to the NIR region. Surface enhancement factors for both crystal violet and adenine were estimated to be on the order of 106 and 108 for gold and silver, respectively. A larger enhancement factor was observed for adenine with NIR excitation than with visible excitation. The benefits of NIR SERS and its potential applications are discussed.
107 citations
TL;DR: In this article, the use of front-surface specular reflection FT-IR spectroscopy to characterize surface orientation in thick samples of poly(ethylene terephthalate) (PET) has been investigated.
Abstract: The use of front-surface specular reflection FT-IR spectroscopy to characterize surface orientation in thick samples of poly(ethylene terephthalate) (PET) has been investigated. It has been shown that, even for samples whose surface uniformity is less than perfect, absorption index spectra of excellent quality are obtained from the Kramers-Kronig transformation. These spectra provide detailed information, both qualitative and quantitative, on the molecular conformation and orientation of the polymer. Of particular interest are the strongly absorbing bands such as the carbonyl and ester peaks, which are generally saturated in transmission spectra. The reflection technique opens up the possibility of obtaining new information on conformational changes and orientation in PET through a detailed study of these peaks.
98 citations
TL;DR: The last decade has seen a significant increase in the utility of Raman measurements in academic, industrial, and governmental laboratories as mentioned in this paper, and applications to polymers, biological systems, process measurements, and many other areas are now possible because of the improvements in the basic spectroscopic instrumentation.
Abstract: The last decade has seen a significant increase in the utility of Raman measurements in academic, industrial, and governmental laboratories. Applications to polymers, biological systems, process measurements, and many other areas are now possible because of the improvements in the basic spectroscopic instrumentation. Most if not all of these improvements have started with new technology, often obtained from other fields, such as holographic filters, charge-coupled-device detectors, and diode-pumped lasers. With the use of this new technology, the performance of the various Raman instruments today offers unparalleled sensitivity and ease of use. This benefit has opened up many new fields where Raman measurements can be applied, as well as making the use of Raman data as easy as it is in the parallel technique of infrared spectroscopy.
TL;DR: In this paper, the authors proposed a scheme to measure standard Raman spectra under a scattering geometry set up on the basis of these vibrational modes, which was able to establish a database for standard spectrum of minerals and related inorganic crystals.
Abstract: Establishing a standard Raman spectral database for minerals and related inorganic crystals is a very important basis for further increasing the applications of Raman spectroscopy in the geosciences. However, the Raman spectral pattern of a crystal is a function not only of its composition and structure but also of the scattering geometry during the measurement. Therefore, the standard Raman spectrum of a crystal must be measured under well-defined standard conditions. It would be of great interest to establish a standard measuring configuration with which the characteristic Raman spectra of all mineral crystals could be obtained. Factor-group analysis of the main types of minerals indicates that almost all of them possess a Raman-active totally symmetric (TS) vibrational mode. Therefore, we propose a scheme to measure standard Raman spectra under a scattering geometry set up on the basis of these TS modes. Using this scheme, we were able to establish a database for standard Raman spectra of minerals and related inorganic crystals.
TL;DR: In this article, the authors compared the diffusion behavior and enrichment from aqueous solutions of three different chlorinated hydrocarbons (CHCs) into different polymers and investigated the influence of polymer properties such as glass transition temperature and crystallinity and the effect of the polymer background IR absorption and varying thicknesses of the polymers to the detectability.
Abstract: Polymer-coated attenuated total reflection (ATR) elements have been used to compare the diffusion behavior and enrichment from aqueous solutions of three different chlorinated hydrocarbons (CHCs)—mono-chlorobenzene (MCB), chloroform (CF), and tetrachloroethylene (TeCE)—into different polymers. The influence of polymer properties such as glass transition temperature and crystallinity and the effect of the polymer background IR absorption and varying thicknesses of the polymer membranes to the detectability were investigated. The crystallinity and the glass transition temperature have a very pronounced influence on the velocity of the diffusion process, whereas the partition coefficient influences the amount of CHC diffusing into the polymer membrane. The time constants for 90% saturation of the polymer with the test analytes are in the range of 8 to 40 min, depending on the nature of the polymer and analyte. A linear calibration graph was obtained for simultaneous detection of all three test analytes in the range from 5 mg/L to 100 mg/L CHC with detection limits of 1.5 to 2 mg/L. Coefficients for CHC partitioning between water and polymers measured by ATR/IR were in good agreement with values determined by GC/MS.
TL;DR: In this article, an optically transparent thin-layer electrochemical (OTTLE) cell was constructed for IR and UV-Vis spectroelectrochemical experiments at variable temperature.
Abstract: This article describes the construction of a novel optically transparent thin-layer electrochemical (OTTLE) cell for IR and UV-Vis spectroelectrochemical experiments at variable temperature The cell has a three-electrode set melt-sealed into a smooth polyethylene spacer which is sandwiched between two CaF2 windows The width of this spacer (018-020 mm) defines the thickness of the thin solution layer The whole electrode assembly is housed in a thermostated Cu block of the OTTLE cell which fits into a double-walled nitrogen-bath cryostat The experimental setup permits relatively fast electrolysis within the tested temperature range of 295 to 173 K under strictly anaerobic conditions and protection of light-sensitive compounds Other important merits of the cell design include lack of leakage, facile cleaning, almost negligible variation of the preset temperature, and facile manipulation in the course of the experiments The applicability of the variable-temperature IR/UV-Vis OTTLE cell is demonstrated by stabilization of a few electrogenerated carbonyl complexes of Mn(I) and Ru(II) with 3,5-di-tert butyl-1,2-benzo(semi)quinone (DB(S)Q) and N,N'-diisopropyl-1,4-diaza-1,3-butadiene (iPr-DAB) ligands, respectively, at appropriately low temperatures
TL;DR: In this article, a XeCl excimer laser was used to focus on a Zn plate in surrounding gas at low pressures (100-1500 Pa), and the characteristics of the resultant plasma were examined with the use of a unique time-resolved spectroscopic method.
Abstract: A XeCl excimer laser (20 ns, 15-70 mJ) has been focused on a Zn plate in surrounding gas at low pressures (100-1500 Pa). The characteristics of the resultant plasma are examined with the use of a unique time-resolved spectroscopic method. A density jump in the distribution of Zn atoms is clearly observed, which indicates the generation of a shock wave. Furthermore, it is proved that the relationships among the displacement length of the front of the emission of the Zn neutral emission line, the pressure of the ambient gas, and the energy of the laser pulse are in good agreement with the theoretical result for a blast wave explosion. An application is also presented to show that the plasma induced by a blast wave is excellent as a light source for emission spectrochemical analysis because of its very low background emission intensity.
TL;DR: In this paper, a laser ablation inductively coupled plasma mass spectrometry (LAICPMS) was applied as a method to determine elemental distribution in biological tissue specimens, providing spatial resolution down to 30 μm with the use of an infrared laser beam.
Abstract: Laser ablation inductively coupled plasma mass spectrometry (LAICPMS) has been applied as a method to determine elemental distribution in biological tissue specimens, providing spatial resolution down to 30 μm with the use of an infrared laser beam. Instrument operating parameters such as the laser energy and "dry plasma" tuning have been optimized to provide the high sensitivity and stability required for this type of analysis. In this work, "natural" internal standards (e.g., calcium and magnesium) have been investigated in an effort to establish and minimize the influence of signal variation associated with the instrumentation and the density of the samples themselves. Specimens studied include fish scales (for "elemental tagging"), rat kidney cross sections, and pig femur (to examine variation in the chemistry of the blood/bone interface).
TL;DR: In this article, a self-modeling multivariate mixture analysis has been developed for the extraction of information about pure components from that kind of mixture, especially when reference spectra are not available.
Abstract: In the analytical environment, spectral data resulting from analysis of samples often represent mixtures of several components. Extraction of information about pure components from that kind of mixture is a major problem, especially when reference spectra are not available. Self-modeling multivariate mixture analysis has been developed for this type of problem. In this paper, two examples will be used to show the potential of the technique for vibrational spectroscopy. Infrared microspectroscopic chemical imaging has been employed to improve spatial resolution for distinguishing differences between adjacent, nonidentical materials. The resolution of a 2- to 3-μm-thick inner layer, from a four-layer polymer laminate, has been achieved. The same approach has been utilized to extract pure component spectra out of a KBr pellet of a mixture of three compounds.
TL;DR: In this paper, the amide A/II band was used as a marker for the strength of hydrogen bonds in amide groups and showed a significant upward shift upon the thermal denaturation of pepsin.
Abstract: FT-NIR spectra have been measured for various polypeptides and proteins with different secondary structures to find an NIR marker band for the structure of the proteins and polypeptides. Their FT-IR spectra have also been obtained to assist in the interpretation of the FT-NIR spectra. Comparison between the FT-NIR and FT-IR spectra shows that there is a clear correlation between the frequency of an NIR band near 4855 cm-1, assignable to a combination of amide A and amide II, and that of an IR band near 3300 cm-1 due to amide A for the polypeptides investigated. Therefore, the NIR band (hereafter, we identify it as amide A/II) may be used as a practical indicator for the strength of hydrogen bonds in the amide groups, as in the case of amide A. The frequency of amide A/II changes little with the secondary structure for both the polypeptides and proteins, and thus it is rather difficult to use this band as a marker band of the secondary structure. For the globular proteins such as hemoglobin, albumin, and lysozyme, irrespective of their secondary structure, both amide A/II and amide A appear in similar positions. However, collagen (Type I, Type IV, and Type V) gives them much higher frequencies, suggesting that the hydrogen bonds in collagen are much weaker than those in typical globular proteins. The amide A/II band shows a significant upward shift upon the thermal denaturation of pepsin. This observation indicates that amide A/II can also be sed for monitoring the destruction of the hydrogen bonds in the amides induced by the denaturation.
TL;DR: The results demonstrate a rapid simple diffuse transmittance measurement of hemoglobin in unlysed blood and the reproducibility of the measurement was 0.63% (<0.1 g/dL).
Abstract: Visible and near-infrared transmittance (T) spectra of unlysed blood samples were obtained with an NIRSystems Model 6500 spectrophotometer modified for an open cell and a vertical light path. Without rigid control of the pathlength and temperature, we were able to measure hemoglobin content within a standard error of 0.43 g/dL using a single-term second-derivative ratio of log(1/T) data at 1740 and 1346 nm. Calibration was done on a set of 104 samples (two spectra of blood from 52 patients) having hemoglobin levels of 6.1 to 19.2 g/dL. Validation was done on an independent set of 56 samples (two spectra of blood from 28 patients) having hemoglobin levels of 7.2 to 19.0 g/dL. The reproducibility of the measurement, tested by computing the coefficient of variability of the 28 duplicated results, was 0.63% (<0.1 g/dL). The results demonstrate a rapid simple diffuse transmittance measurement of hemoglobin in unlysed blood.
TL;DR: In this article, the Fourier transform Raman (FT-R) spectra of polyiodides were used for resonance Raman spectroscopy and the results showed that the results were consistent with the I-·2I2, I3-I2 and I3·I2 descriptions.
Abstract: In resonance Raman (RR) spectroscopy, the laser excitation sources have often been found to be destructive towards polyiodides if compared with the milder conditions under which the Fourier transform Raman (FT-R) technique operates. In fact, our FT-R spectra of some model polyiodides—[(CH3)4]I5 (I5-bent), [(C2H5)4N]l7, and [(CH3)4N]I9—are significantly different from the literature RR data, give evidence of decomposition of the samples in RR, and are in agreement, respectively, with the I-·2I2, I3-·2I2 and (I-·2I2)·2I2 descriptions. In addition to the above-cited cases, the FT-R spectra of [Mn(modtc)3]I5 (modtc = morpholine carbodithioato) and [moH]I5 (moH = morpholinium) are reported. The crystal structures indicate that in these two compounds the I5- anions can be properly described as I-·2I2 and I3-·I2, respectively, and FT-R spectra agree well with this formulation. Moreover, the first FT-R spectrum of an I164- anion in [mo2ttl]2I16, ([mo2ttl]2+ = 3,5-di(N-morpholinio)-1,2,4-trithiolane), whose X-ray structure shows a sequence of two I3- ... I2 ... I-·I2 (I82-) interacting anions, is reported. A close correlation of the FT-Raman peaks with the molecular species, identified by the inter-atomic distances, is also observed in this case. Thus, a combination of X-ray structural data and FT-R data can provide a reasonable interpretation of the nature of the acceptor iodine moiety in charge-transfer polyiodide complexes.
TL;DR: In this article, a model of laser ablation and the subsequent interaction of ablated graphite particles with the laser-induced plasma was proposed to estimate the particle size of carbon thin films.
Abstract: Mechanisms of the deposition of carbon thin films by the laser ablation of graphite were investigated by monitoring the plasma emission. Parameters such as electron density, ionization temperature, and vibrational temperature during plasma growth were evaluated as a function of the laser power density and the surrounding atmosphere. Also, Raman spectra of the deposited films were measured so that the particle size can be estimated from the intensity ratio of the Raman bands around 1360 and 1580 cm-1, The increase in power density caused an increase in ionization temperature and vibrational temperature of carbon species in the plasma but a decrease of particle size of the deposited thin films. The existence of 10 Torr of helium as a surrounding atmosphere caused drastic changes in the plasma parameters. The films deposited with helium atmosphere showed a low optical band gap, which indicates heat restructuring of ablated graphite particles in the hot plasma. The results can be explained with a simple model of laser ablation and the subsequent interaction of ablated particles with the laser-induced plasma.
TL;DR: In this article, the peak positions and bandwidths of the first-order Raman bands, in the region 100 to 500 cm-1, were used as a measure of crystalline order.
Abstract: Crystalline disorder in thin films plays an important role in determining their properties. Disorder in the crystal structure of MoS2 films prepared by magnetron sputtering and pulsed laser deposition was evaluated with the use of Raman spectroscopy. The peak positions and bandwidths of the first-order Raman bands, in the region 100 to 500 cm-1, were used as a measure of crystalline order. In addition, a low-frequency feature was observed at 223 cm-1 that is not part of the normal first-order spectrum of a fully crystalline specimen. Data presented here demonstrate that this band is characteristic of crystalline disorder, and its intensity depends on the annealing history of the film. This behavior seems to be analogous to the disorder found in graphite thin films.
TL;DR: In this article, the effects of different types of artificial weathering conditions on the chemical composition of wood have been investigated, such as light only, water only, and light plus water.
Abstract: Diffuse reflectance infrared spectroscopy has been used to monitor the changes in functional groups on the surface of two woods (western redcedar and southern pine) when they are subjected to a range of artificial weathering conditions. The effects of light only, water only, and light plus water have been studied for a variety of exposure times. The changes in the chemical composition of the wood caused by light plus water is considerably greater than that caused by light only, whereas water alone causes no permanent chemical changes. The effects of some of these weathering conditions have been investigated for wood protected by varnish, for earlywood and latewood and for tangentially, radially, and cross-sectionally cut wood samples. The application of two coats of varnish was found to considerably reduce the weathering effects caused by UV radiation; earlywood undergoes light-only degradation faster than late wood; and the effect of weathering was found to be greatest for cross-sectional cut samples and least for radially cut samples. The weathering profile with depth of penetration has been studied in some detail for western redcedar, and our results show that, after 300 h of continual artificial weathering, the chemical changes are confined to the first 200 μm.
TL;DR: In this paper, a laser-induced breakdown spectroscopy (LIBS) was used in simultaneous quantitative elemental analysis of NIST transition metal alloy samples, where a plasma was formed by focusing a Nd:YAG laser onto the sample's surface inside a vacuum chamber.
Abstract: Laser-induced breakdown spectroscopy (LIBS) in an ultra-high vacuum is used in simultaneous quantitative elemental analysis of NIST transition metal alloy samples. A plasma is formed by focusing a Nd:YAG laser onto the sample's surface inside a vacuum chamber. UV-visible emission from excited species is monitored with the use of an optical multichannel analyzer (OMA). Linear calibration curves are shown for the elements (percent composition) Al (0.2-1.2%), Cu (0.021-0.49%), Fe (4.5-51.0%), Ni (30.8-80.3%), and Zn (6-12.8%) with the use of nonresonant lines. Detection limits (signal-to-noise = 3) vary with sample composition complexity from 0.0001% for Ni in a simple copper alloy (SRM 1111) to 0.16% for Al in a complex granular sample (SRM 349a). Absolute detection limits are estimated to be in the 20-200 μg/g range for the elements of interest. Simultaneous mass spectra were taken by sweeping the magnetic field of a mass spectrometer. Preliminary results showed the magnet could not be swept fast enough for multielement analysis. The use of a position-sensitive ion detection system is proposed.
TL;DR: In this paper, the authors used NIR spectroscopy for nondestructively discriminating tablets containing an active drug from two placebo tablet formulations inside blister-packaged clinical supplies without removing the tablets from the blind study tablet cards.
Abstract: Near-infrared spectroscopy was evaluated as a method for nondestructively discriminating tablets containing an active drug from two placebo tablet formulations inside blister-packaged clinical supplies without removing the tablets from the blind study tablet cards. A custom sampling device was constructed to allow the spectra of individual tablets to be collected. Spectra of 165 tables were acquired over the wavelength range of 400 to 2500 nm. These tablets were of two different sizes and three formulations. The second derivatives of the spectra were calculated and randomly divided into two groups, each containing approximately half the samples. A factor-based library/model was constructed with the use of the second-derivative spectra from one of the groups over the wavelength range from 1600 to 2500 nm. The model was then validated by predicting the identity of the tablets in the remaining group. The identity and formulation of all the tablets were correctly predicted. This model was then used to confirm the identity of thousands of clinical trial samples. Apart from being nondestructive, the NIR method is less labor and time intensive than the previously used TLC assay.
TL;DR: In this paper, the authors present accurate infrared absorption intensities of liquid toluene at 25°C. The accuracy is estimated from the agreement between the intensities measured by different spectroscopists using the same instrument in the same laboratory and also by different scientists in different laboratories using instruments made by different manufacturers.
Abstract: This paper presents accurate infrared absorption intensities of liquid toluene at 25°C. The accuracy is estimated from the agreement between the intensities measured by different spectroscopists using the same instrument in the same laboratory and also by different spectroscopists in different laboratories using instruments made by different manufacturers. The average agreement between integrated intensities over specific wavenumber ranges is about ±1.8%. The spectra from the different laboratories have been averaged, unweighted, to give intensity spectra of toluene that are presented as the best available. The use of data from different instruments in different laboratories has included the influence of systematic instrumental errors, so that the precision of the intensity data presented should be a better approximation to its accuracy than would be the case from an extensive study by one person on one instrument. The results obtained agree with the only measurements that have been made against a primary standard, the estimated accuracy of which is about 6%. The results are presented as graphs and tables of the molar absorption coefficient spectrum and the real and imaginary refractive index spectra between 6500 and 435 cm-1. The peak heights and the areas under the bands in the imaginary refractive index (i.e., absorption index) and molar absorption coefficient spectra are reported. The absorption index, k(v), and molar absorption coefficient, Em(v), values are believed to be accurate to an average ±2.5% at the peaks of 39 strong, medium, and weak bands and ±1.9% at the peaks of 51 very weak bands below 4100 cm-1. Above 4100 cm-1, 11 very weak bands have an average accuracy of ±1.3%. The baseline k(v) values are accurate to between ±3 and ±10%. The areas under bands or band groups in k(v) and ɛm(v) spectra are accurate to 2.4% on average, or 1.2% for strong, medium, and weak band groups between 3150 and 775 cm-1 with 0.002 < kmax < 0.112. The real refractive index, n(v), values are believed to be accurate to 0.2%.
TL;DR: A flow injection system incorporating a microcolumn of activated alumina was combined with inductively coupled plasma mass spectrometry for on-line trace enrichment and determination of uranium in surface waters and sea water as discussed by the authors.
Abstract: A flow injection system incorporating a microcolumn of activated alumina was combined with inductively coupled plasma mass spectrometry for on-line trace enrichment and determination of uranium in surface waters and sea water. Deposition of uranium was effected with the use of a basic alumina microcolumn, and injection of nitric acid (250 μL, 2M) served to elute retained species to the ICP. A sample volume of 14 mL resulted in a preconcentration factor of 40, and precision at the 50-ng 1-1 level was 4.5% (RSD). The procedure was applied to mineral waters, river water, and sea water, and accuracy was assessed through either analysis of certified reference waters or recovery experiments.
TL;DR: In this article, the thermally induced breakdown of ethylene-vinyl acetate (EVA) copolymers was studied, and it was shown that EVA undergoes a two-step decomposition: an acetate pyrolysis of the copolymer leaving a polyunsaturated linear hydrocarbon, followed by the breakdown of the hydrocarbon backbone to produce a large number of straight-chain hydrocarbon products.
Abstract: With a combination of information from TG/IR and GC/IR measurements of the trapped gases, characterization of complex polymer decompositions can be made. In this paper, the thermally induced breakdown of ethylene-vinyl acetate (EVA) copolymers was studied. Results show that EVA undergoes a two-step decomposition: an acetate pyrolysis of the copolymer leaving a polyunsaturated linear hydrocarbon, followed by the breakdown of the hydrocarbon backbone to produce a large number of straight-chain hydrocarbon products.
TL;DR: In this paper, the infrared spectra of trimethyl phosphate (TMP), triethyl phosphate and tri-n-butyl phosphate were obtained for argon and nitrogen matrices, and the peak widths of the sharpest features in matrix-isolated spectra were typically 2 cm-1.
Abstract: Matrix-isolation infrared spectra of trimethyl phosphate (TMP), triethyl phosphate (TEP), and tri-n-butyl phosphate (TBP), in argon and nitrogen matrices, are reported for the first time. The peak widths of the sharpest features in our matrix-isolated spectra are typically 2 cm-1, compared with peak widths of 40 cm-1 seen in liquids for these compounds. Comparison with the vapor-phase spectrum of TMP reported earlier indicates that TMP is trapped in two different conformations in these matrices. Similar spectra were also obtained for TEP. Our matrix-isolated spectra indicate that the intramolecular hydrogen bonding (which is believed to be responsible for the lowering of the P=O frequency in the C3, conformer relative to the C3 conformer in these compounds) is stronger in TEP than in TMP. In the case of TBP, the peak widths were larger (8-10 cm-1) than those obtained for TMP and TEP. This observation is probably due to a distribution of conformers that may be trapped in the matrix, as a result of the increased alkyl chain length in TBP.
TL;DR: In this article, it was shown that ES-MS is suitable for the direct determination of ionic species in solution and that it is applicable to the determination of organometallic compounds.
Abstract: Electrospray mass spectrometry (ES-MS) is shown to be suited for the direct determination of ionic species in solution. Examples used in this investigation of ES-MS for elemental speciation determinations included several inorganic ionic species of chlorine, iodine, sulfur, and iron. These species were differentiated on the basis of differences in the molecular form and/or the oxidation state of the analyte ion. The inorganic complexes of silver-cyanide and iron-fluoride were also measured in this assessment. Finally it is shown that ES-MS is applicable to the determination of organometallic compounds. While ES-MS is not an ideal speciation technique, there is considerable evidence to indicate that ES-MS can become an invaluable tool with which species distributions in a wide range of sample types may be probed.