Showing papers in "Applied Spectroscopy in 2002"
TL;DR: In this paper, the effect of surface-enhanced Raman scattering (SERS) is exploited to detect the native chemical constituents of living cells, such as DNA and phenylalanine.
Abstract: Ultrasensitive Raman measurements in single living cells are possible through exploiting the effect of surface-enhanced Raman scattering (SERS). Colloidal gold particles (60 nm in size) that are deposited inside cells as "SERS-active nanostructures" result in strongly enhanced Raman signals of the native chemical constituents of the cells. Particularly strong field enhancement can be observed when gold colloidal particles form colloidal clusters. The strongly enhanced Raman signals allow Raman measurements of a single cell in the 400-1800 cm-1 range with 1-μm lateral resolution in relatively short collection times (1 second for one mapping point) using 3-5 mW near-infrared excitation. SERS mapping over a cell monolayer with 1-μm lateral resolution shows different Raman spectra at almost all places, reflecting the very inhomogeneous chemical constitution of the cells. Colloidal gold supported Raman spectroscopy in living cells provides a tool for sensitive and structurally selective detection of native chemicals inside a cell, such as DNA and phenylalanine, and for monitoring their intracellular distributions. This might open up exciting opportunities for cell biology and biomedical studies.
583 citations
TL;DR: In this paper, the authors compared the electronic structure of molecules and solid-state materials such as semiconductors, and found that molecules have the same energy gap as insulators.
Abstract: C rystalline inorganic so lids can be divided electronically into three well-known classes: metals, semiconductors, and insulators. In these extended solids, atomic orbitals overlap to give nearly continuous electronic energy levels known as bands.1 Metals are electronically characterized by having a partially lled band; semiconductors have a lled band (the valence band) separated from the (mostly) empty conduction band by a bandgap Eg, corresponding to the familiar HOMOLUMO energy gap for small molecules. Insulators are conceptually the same as semiconductors in their electronic structure, except that the bandgap is larger in insulators (Fig. 1). In terms of Egs, metals have Eg less than ;0.1 eV; semiconductors have Egs from ;0.5 to ;3.5 eV; and insulators have Eg . ;4 eV. (1 eV 5 1.602 3 10219 J 5 8065.5 cm21). There are some key differences, however, between the electronic structure of molecules and solid-state materials such as semiconductors.
207 citations
TL;DR: In this article, several algorithms are proposed to achieve automatic fluorescence rejection (AFR) based on shifted excitation Raman difference spectroscopy, which is mathematically linear and can be automated.
Abstract: Sample fluorescence is detrimental to Raman spectroscopic analysis. Several algorithms are proposed to achieve automatic fluorescence rejection (AFR) based on shifted excitation Raman difference spectroscopy. The algorithms are mathematically linear and can be automated. The methods are based on a wavelength-tunable laser and the measurement and calibration of both the Raman and the excitation spectra. Applying the AFR methods to highly fluorescent samples significantly reduces the fluorescence background and reveals weak Raman features unidentifiable using traditional methods. Fixed pattern "noise" associated with the background can be completely removed. The merits of each algorithm are discussed and the best excitation frequency shift to perform the analysis is found to be comparable to the widths of major Raman peaks.
179 citations
TL;DR: In this paper, partial least-squares regression (PLS) was used to estimate the active substance content of a pharmaceutical tablet using NIR transmittance and Raman spectroscopy chemometric calibrations.
Abstract: In this study, near-infrared (NIR) transmittance and Raman spectroscopy chemometric calibrations of the active substance content of a pharmaceutical tablet were developed using partial least-squares regression (PLS). Although the active substance contained the strongly Raman active C≡N functional group, the best results were obtained with NIR transmittance, which highlights the difference between (microscopic) surface sampling and whole tablet diffuse transmittance sampling. The tablets exist in four dosages with only two different concentrations of active substance (5 mg (5.6% w/w), and 10, 15, and 20 mg (8.0% w/w) active substance per tablet). A calibration on all four dosages resulted in a prediction error expressed as the root mean squared error of cross-validation (RMSECV) of 0.30% w/w for the NIR transmittance calibration. The corresponding error when using Raman spectra was 0.56% w/w. Specially prepared calibration batches covering the range 85-115% of the nominal content for each dosage were added to the first sample set, and NIR transmittance calibrations on this set - containing coated as well as uncoated tablets - gave a further reduction in prediction errors to 0.21-0.289% w/w. This corresponds to relative prediction errors (RMSECV/ynom) of 2.6-3.7%. This is a reasonably low error when compared to the error of the chromatographic reference method, which was estimated to 3.5%.
178 citations
TL;DR: Vapor generation is a widespread method used for the determination of metals, metalloids, and organometallic compounds as mentioned in this paper, which may result in their transfer from a condensed phase to the gas phase.
Abstract: V apor generation is a widespread method used for the determination of metals , metalloids, and organometallic compounds. Contrary to common belief, a signi cant number of metal(oid)s form volatile species, many of which occur in nature. Vapor generation is a process wherein nonvolatile (usually ionic-metallic or organometallic) compounds form volatile or semivolatile species through chemical, physical, or biological processes that may result in their transfer from a condensed phase to the gas phase. It is now well known that numerous volatile and semivolatile metal compounds are present in our environment as a consequence of both anthropogenic and natural processes. For example, metal hydrides can be formed in many environmental settings where reducing conditions prevail. Donard 1 noted release of tin hydride from a model seawater-sediment system more than ten years ago. Several reports have also highlighted detection of metal hydrides
162 citations
TL;DR: In this article, Fourier transform infrared (FT-IR) spectroscopy is used for characterizing waste organic matter, its decomposition, and stabilization in rotting processes, using a specific set of differently treated input materials, originating from various composting plants.
Abstract: A series of experiments has shown that FT-IR (Fourier transform infrared) spectroscopy is a helpful tool for characterizing waste organic matter, its decomposition, and stabilization in rotting processes. A specific set of differently treated input materials, originating from various composting plants, was chosen to reflect a wide range of spectroscopic properties. The approach to FT-IR spectra interpretation is presented. Changes of relative absorbances of the band at 2925 cm-1 (methylene groups of aliphatics) reflect the progress and dynamics of composting processes. Different processes can be compared by the specific development of their 2925 cm-1 band. Nitrate was quantified by calibrating nitrate band heights with added amounts of KNO3. The concentrations and band heights (absorbances) were linearly correlated (R2 = 0.9968, SD = 0.001). Bands of inorganic components are useful to assess the decomposition process because they also indicate the development of organic matter. Different wastes can be distinguished by their fingerprint region (1500-900 cm-1). This region also reveals fresh and undecomposed materials. The presence or absence of specific bands provides information about the decomposition status of materials.
129 citations
TL;DR: In this paper, an extended inverted signal correction (EISC) method for separating scattering from absorbance in spectroscopic measurements is presented and compared to multiplicative signal correction and existing modifications of this.
Abstract: A new extended method for separating, e.g., scattering from absorbance in spectroscopic measurements, extended inverted signal correction (EISC), is presented and compared to multiplicative signal correction (MSC) and existing modifications of this. EISC preprocessing is applied to near-infrared transmittance (NIT) spectra of single wheat kernels with the aim of improving the multivariate calibration for protein content by partial least-squares regression (PLSR). The primary justification of the EISC method is to facilitate removal of spectral artifacts and interferences that are uncorrelated to target analyte concentration. In this study, EISC is applied in a general form, including additive terms, multiplicative terms, wavelength dependency of the light scatter coefficient, and simple polynomial terms. It is compared to conventional MSC and derivative methods for spectral preprocessing. Performance of the EISC was found to be comparable to a more complex dual-transformation model obtained by first calculating the second derivative NIT spectra followed by MSC. The calibration model based on EISC preprocessing performed better than models based on the raw data, second derivatives, MSC, and MSC followed by second derivatives.
117 citations
TL;DR: In this paper, a new analytical method based on the Raman spectroscopy of the ν(OH) stretching vibration of water was developed for the determination of the concentration of chloride in aqueous solutions with the goal of reconstructing the bulk ion content of fluid inclusions that are relics of paleo-fluid circulation in rocks.
Abstract: A new analytical method, based on the Raman spectroscopy of the ν(OH) stretching vibration of water, has been developed for the determination of the concentration of chloride in aqueous solutions with the goal of reconstructing the bulk ion content of fluid inclusions that are relics of paleo-fluid circulation in rocks. The method involves calibrating the area of one band of the spectrum difference between pure water and solutions of appropriate composition with respect to the chloride concentration. Calibration curves were constructed for the major geological chemical salts LiCl, NaCl, KCl, CaCl2, and MgCl2, and NaCl-CaCl2 systems. The application to fluid inclusions has been confirmed using synthetic fluid inclusions. For cubic minerals such as fluorite, the calibration curve for the NaCl system correctly estimates the chlorinity. For birefringent minerals, such as quartz, the Raman spectrum of the aqueous solution depends on the orientation of the host crystal. The crystal must be oriented in such a way that one axis of the ellipse of the indicatrix projects parallel to the spectrometer slit. This method complements micro-thermometric data and allows the determination of chlorinity when ice-melting temperature cannot be used.
110 citations
TL;DR: In this article, the influence of the matrix on the laser-induced spectroscopy of magnesium was investigated, and a relative error of ~10% and a precision of 10-20% were obtained for the determination of Mg in several certified samples.
Abstract: The goal of this research was to investigate the influence of the matrix on the laser-induced spectroscopy of magnesium. Powdered samples were used and were presented to the measurement as thin distributions on adhesive tape. A wide range of NIST certified reference materials were used as samples. With careful sample preparation and correction for sample surface density on the tape (determined by weighing), reasonable consistency in the Mg signal intensity was obtained regardless of sample matrix. Relative error of ~10% and a precision of 10-20% were obtained for the determination of Mg in several certified samples.
102 citations
TL;DR: In this article, the use of remote pulsed laser Raman spectroscopy for mineral analysis at distances from 10 to 66 m on planetary surfaces has been explored using a small pulsed Nd:YAG laser and a 5-in. telescope coupled to a spectrograph with an optical fiber.
Abstract: There is a need for an instrument that can be used for remote in situ identification of biogenic and a-biogenic minerals, various types of ices, and organic and inorganic materials on planetary surfaces. In this paper, we explore the use of remote pulsed laser Raman spectroscopy for mineral analysis at distances from 10 to 66 m on planetary surfaces. We have constructed a remote Raman system utilizing a small pulsed Nd:YAG laser and a 5-in. telescope coupled to a spectrograph with an optical fiber. The performance of our system is demonstrated by presenting spectra of benzene and marble (calcium carbonate) while varying the integration time (i.e., number of laser shots), as well as single laser shot spectra of marble while decreasing laser power. Finally, Raman spectra of representatives of several different mineral groups are presented, including hydrated substances, carbonates, silicates (e.g., olivine, pyroxene, feldspars, etc.), water, and ice.
96 citations
TL;DR: In this paper, a combination of Fourier transform infrared (FT-IR) spectroscopy and microscopy, FT-IR microspectroscopy, has been used to characterize sections of human colorectal adenocarcinoma.
Abstract: A combination of Fourier transform infrared (FT-IR) spectroscopy and microscopy, FT-IR microspectroscopy, has been used to characterize sections of human colorectal adenocarcinoma. In this report, a database of 2601 high quality FT-IR point spectra from 26 patient samples and seven different histological structures was recorded and analyzed. The computer-based analysis of the IR spectra was carried out in four steps: (1) an initial test for spectral quality, (2) data pre-processing, (3) data reduction and feature selection, and (4) classification of the tissue spectra by multivariate pattern recognition techniques such as hierarchical clustering and artificial neural network analysis. Furthermore, an example of how spectral databases can be utilized to reassemble false color images of tissue samples is presented. The overall classification accuracy attained by optimized artificial neural networks reached 95%, highlighting the great potential of FT-IR microspectroscopy as a potentially valuable, reagent-free technique for the characterization of tissue specimens. However, technical improvements and the compilation of validated spectral databases are essential prerequisites to make the infrared technique applicable to routine and experimental clinical analysis.
TL;DR: In this paper, the authors investigated the Raman spectrum of heme myoglobin adsorbed on silver colloidal nanoparticles at very low concentrations and found that the single molecule limit is approached.
Abstract: The extremely large cross-section available from metallic surface enhancement has been exploited to investigate the Raman spectrum of heme myoglobin adsorbed on silver colloidal nanoparticles at very low concentrations. The study has been performed on particles both in solution and immobilized onto a polymer-coated glass surface. In both the cases, we have observed striking temporal fluctuations in the surface-enhanced resonance Raman spectroscopy (SERRS) spectra collected at short times. A statistical analysis of the temporal intensity fluctuations and of the associated correlations of the Raman signals has allowed us to verify that the single molecule limit is approached. The possible connections of these fluctuations with the entanglement of the biomolecule within the local minima of its rough energy landscape is discussed.
TL;DR: In their modiµ ed forms, room-temperature ionic liquids (RTILs), with no measurable vapor pressure, can be used as replacements for select organic solvents as discussed by the authors.
Abstract: One of the biggest problems posed to the chemical industry is to continuously deal with the fact that all chemical plants rely heavily on toxic, hazardous, and ammable organic solvents. Newly rediscovered (in their modi ed forms) room-temperature ionic liquids (RTILs), with no measurable vapor pressure, can be used as replacements for select organic solvents. RTILs are organic salts composed of anions and cations that are in liquid state at ambient conditions. The new generation of RTILs have the potential to act as environmentally benign solvent media for many industrially important chemical processes.1 Recently, these novel RTILs have shown promise toward important applications such as synthesis, catalysis, polymerization, separation, and extraction processes. 2 The RTILs utilized in the aforementioned applications are usually prepared according to the most effective synthetic procedure. Current literature on RTILs indicates that some research groups occassionally prepare their own RTILs, while others purchase RTILs that are commercially available. However, it is fairly clear that the synthetic pathways involved in the preparation of RTILs can introduce a variety of impurities, such as residual sodium and chloride ions, organic impurities, and, per-
TL;DR: In this article, the ion exchange polymer membrane was used to concentrate and immobilize the metal ions and then ablated with the focused energy of a Nd:YAG laser at 1064 nm.
Abstract: Elemental analysis of solutions can be achieved by concentrating and immobilizing the metal ions into a commercially available ion exchange polymer membrane followed by laser-induced breakdown spectroscopy. Two methods of sample preparation were investigated: filtering the solution through the ion exchange membrane with suction, and placing the membrane in the solution and allowing the ions to equilibrate with the membrane. The membrane was then ablated with the focused energy of a Nd:YAG laser at 1064 nm. The emitted light was collected by an echelle spectrometer through a fiber-optic cable and detected with an intensified charge-coupled device (CCD). Ten different metals, most covered by the Resource Conservation and Recovery Act (RCRA), were studied. The concentrations of barium, cadmium, chromium, cobalt, copper, silver, lead, mercury, nickel, and zinc can be measured simultaneously with limits of detection ranging from 2 μg/mL to 4 ng/mL. The linear range is 2-6 orders of magnitude depending upon the element and sampling method. The major advantages of the technique are the multielement capability and the ease of sample preparation.
TL;DR: In this article, the authors used fiber-optics reflectance spectroscopy to identify pigments in pictorial layers of works of art thanks to a spectra database of dry powdered mineral pigments.
Abstract: Fiber-optics reflectance spectroscopy is used to identify pigments in pictorial layers of works of art thanks to a spectra database of dry powdered mineral pigments. Measurements are noninvasive, without any contact, and can be implemented in situ, without moving the work of art under investigation from its conservation place. The experimental device, using the special back-scattering configuration, is briefly presented. The protocol leading to the constitution of the spectra database of dry mineral pigments is described. Unlike other studies, this protocol has been developed to emphasize multiple scattering of light by elementary pigments in comparison with specular reflection on the surface of the sample. In these conditions, the diffuse reflectance spectrum is the label of the mineral pigment. The numerical processing of pigment identification is detailed. Both the influences of the roughness of the studied surface and of a possible varnish layer are taken into account when numerical identification is implemented. Several applications on patrimonial works of art are reported.
TL;DR: In this paper, the authors reported a system for collecting spectrally resolved fluorescent lifetime images, which was combined with two-dimensional spectral imaging in a programmable array microscopy (sFLIM) system with a resolution of 50λ/Δλ and a wavelength range of ~430-750 nm.
Abstract: We report a system for collecting spectrally resolved fluorescent lifetime images. Frequency domain fluorescence lifetime detection was combined with two-dimensional spectral imaging in a programmable array microscope. The spectroscopic fluorescence lifetime imaging microscopy (sFLIM) system has a resolution of ~50 (λ/Δλ) in the current arrangement and a wavelength range of ~430-750 nm. With the sFLIM system, we recorded the lifetime spectra of rhodamine 6G, rhodamine B, and the DNA intercalation dye propidium iodide (PI) in cuvettes and an EGFP-fusion of the histone 2A variant D protein in Drosophila salivary gland explants in the presence and absence of PI. In the absence of PI, the EGFP-fusion exhibited a lifetime of 2.7 ns with little variation in wavelength. The lifetime of PI alone ranged from ~1 ns in buffer to ~18 ns when intercalated in the nuclei of intact cells. The combination of EGFP and PI in the Drosophila salivary gland explants exhibited strong fluorescence resonance energy transfer (FRET), a result consistent with the known nucleosomal structure of eukaryotic chromatin.
TL;DR: In this paper, the authors investigated the relationship between thickness and absorption of cellulose and found that the relationship was exponential with the wavelength and had an exponential relationship with the thickness of the cellulose substrate.
Abstract: The depth near-infrared (NIR) radiation penetrates into a sample during spectral acquisitions in NIR reflectance microscopy was investigated for pharmaceutical materials. Cellulose and its derivatives are widely used as excipients for pharmaceuticals and hence, were the basis for this study. The evaluation of the depth of sample contributing to the measured reflected radiation (information depth) was achieved using varying thicknesses of cellulose placed on top of a substrate. Analyzing the change in the absorption profile of the substrate showed the relationship between thickness and absorption to be exponential. The information depth was evaluated using the point where the substrate signal was reduced by 50%, termed the DP50 value. The DP50 value ranged from 39 to 61 μm at ~1675 nm, but was found to have an exponential relationship with wavelength. Longer wavelengths had less penetration into the sample; at 2380 nm the DP50 was ~27 μm but this increased to ~180 μm at 1100 nm. The sample size was determined using the information depth and an approximate model for the contributing sample volume. Sample size was found to be within the range of 0.03-418 μg of sample per NIR spectrum depending on the wavelength used.
TL;DR: In this paper, a methodology that allows identification and quantitative determination of individual acidic and neutral diterpenes in natural mixtures, using the computer-aided analysis of their 13C-NMR spectra, was presented.
Abstract: We report a methodology that allows identification and quantitative determination of individual acidic and neutral diterpenes in natural mixtures, using the computer-aided analysis of their 13C-NMR spectra The analytical procedure was validated on artificial mixtures and then applied to authentic oleoresins of Pinus nigra Up to eleven diterpenes, which represented 63% of the total composition of the oleoresin, were identified and quantified without previous separation or derivatization
TL;DR: Time-resolved spectroscopy in the visible and near-infrared (NIR) regions was used in a feasibility study for analysis of solid pharmaceuticals as discussed by the authors, where the light was focused onto the surface of tablets, and the transmitted light was detected by a time-resolving streak camera.
Abstract: Time-resolved spectroscopy in the visible and near-infrared (NIR) regions was used in a feasibility study for analysis of solid pharmaceuticals. The objective of the experiments was to study the interaction of light with pharmaceutical solids and to investigate the usefulness of the method as an analytical tool for spectroscopic analysis. In these experiments, a pulsed Ti:sapphire laser and white light generation in water was utilized to form a pulsed light source in the visible/NIR region. The light was focused onto the surface of tablets, and the transmitted light was detected by a time-resolving streak camera. Two types of measurements were performed. First, a spectrometer was put in front of the streak camera for spectral resolution. Secondly, the signal originating from different locations of the sample was collected. Time-resolved and wavelength/spatially resolved data were generated and compared for a number of different samples. The most striking result from the experiments is that the typical optical path length through a 3.5-mm-thick tablet is about 20-25 cm. This indicates very strong multiple scattering in these samples. Monte Carlo simulations and comparison with experimental data support very high scattering coefficients on the order of 500 cm-1. Furthermore, the data evaluation shows that photons with a particular propagation time through the sample contain a higher chemical contrast than other propagation times or than steady-state information. In conclusion, time-resolved NIR spectroscopy yields more information about solid pharmaceutical samples than conventional steady-state spectroscopy.
TL;DR: In this paper, a simplified preferential solvation model based on the weighted mole-fraction probe response was used to evaluate the hydrogen-bond-donating ability of room-temperature ionic liquids (RTILs).
Abstract: Room-temperature ionic liquids (RTILs) have shown tremendous promise as replacements for the toxic and volatile organic solvents used in many applications. Depending on a particular application, addition of a "green" cosolvent can very easily modify/alter the physicochemical properties of the RTILs in a favorable fashion. Solvatochromic probe behavior within binary RTIL 1-butyl-3-methyl imidazolium hexafluorophosphate (BMIMPF6) + ethanol solutions are investigated using four popular probes, pyrene, 1-pyrenecarboxaldehyde, 1,3-bis-(1-pyrenyl)propane, and Reichardt's betaine dye. A simplified preferential solvation model based on the weighted mole-fraction probe response shows that the pyrene cybotactic region is rich in BMIMPF6 in comparison to the bulk composition. However, 1-pyrenecarboxaldehyde and 1,3-bis-(1-pyrenyl)propane solvation environments clearly indicate a cybotactic region dominated by ethanol. Reichardt's betaine dye shows absorbance maxima lower than that observed in either of the two neat components, BMIMPF6 or ethanol. This probe is well known to manifest the hydrogen-bond-donating (HBD) ability of the solvent system. HBD ability also depends on the dipolarity/polarizability of the solvent system. Ethanol has a higher HBD ability but lower dipolarity/polarizability than BMIMPF6. As the mole fraction of ethanol is increased, the increase in the HBD ability of the binary BMIMPF6 + ethanol solution is manifested through the unusual Reichardt's dye response.
TL;DR: In this article, a Raman spectrum of single nanometer-sized particles (nano-particles) trapped by laser tweezers was obtained for the first time using an oil-immersed objective lens with high numerical aperture.
Abstract: We have obtained a Raman spectrum of single nanometer-sized particles (nano-particles) trapped by laser tweezers for the first time. The microscope used in this study is a new version of our Raman tweezers microscope (RTM); it contains an oil-immersed objective lens with high numerical aperture to increase the force of the optical radiation pressure of the near-infrared laser beam to trap single organic and biological nanoparticles and provides sufficient sensitivity for the Raman measurement of the trapped nano-particles. The confocal arrangement in the system completely eliminates the Raman signal of the oil under the objective lens. The RTM provides a Raman spectrum of a single polystyrene latex bead about 40 nm in diameter with an exposure time of 3 s and allows us to determine its molecular species. Furthermore, the RTM enables us to count the number of nanoparticles in the focal spot of the laser beam from the Raman spectra of trapped nanoparticles.
TL;DR: In this paper, the essential oils of various commercial citrus species were studied by ATR/FT-IR as well as NIR-FT Raman spectroscopy using principal component analysis (PCA).
Abstract: The essential oils of various commercial citrus species were studied by ATR/FT-IR as well as NIR-FT Raman spectroscopy. Some of the most relevant monoterpene components occurring in the oil, such as limonene and γ-terpinene, show characteristic key bands in the IR and Raman spectra, which are useful for making a quantitative distinction between different oil types. Applying principal component analysis (PCA) to the spectral data, the individual citrus products are located, in most cases, as separated clusters in a 3-dimensional factor space. Cross-validation statistics showed that a partial least-square (PLS) algorithm was able to produce high quality predictions of the relative oil composition as well as general quality parameters. Both complementary spectroscopic techniques described in this study have the potential to replace existing analytical procedures because they are capable of faster quality control measurements and they allow on-line analyses during distillation or extraction processes to be performed.
TL;DR: In this paper, the distribution of poly(tetrafluoroethylene) clusters of 10 to 30 μm are randomly distributed in a polyamide matrix and silicone oil can be found at the cluster matrix interface.
Abstract: Morphological studies were performed on a polymer blend, used as a friction bearing, consisting of polyamide 6.6 (80%), poly-(tetrafluoroethylene) (18%), and silicone oil (2%). Raman imaging, FT-IR imaging, scanning electron microscopy with energy-dispersive X-ray spectrometry, and microthermal analysis determined the distribution of poly(tetrafluoroethylene) clusters in the polyamide matrix. Each characterization method allows qualitative identification of the main components and provides information about cluster size and distribution. It is proved that poly(tetrafluoroethylene) clusters of 10 to 30 μm are randomly distributed in a polyamide matrix and that silicone oil can be found at the cluster matrix interface. The good agreement that was obtained in our investigations indicates high reliability of the results since all applied methods are based on different chemical and physical properties. This combined approach revealed information about the morphology of the blend for a better understanding of its working principle and enhanced knowledge for its processing. A comparison of the different methods employed in this study highlights their advantages and limitations for polymer analyses.
TL;DR: In this paper, the effect of particle size on Raman intensity has been measured for a number of crystalline solids with a fiber-optic-based Raman spectrometer.
Abstract: The effect of particle size on Raman intensity has been measured for a number of crystalline solids with a fiber-optic-based Raman spectrometer. Particle sizes ranged from 76 to 605 μm. Materials examined were sodium nitrate, sodium chlorate, sodium bromate, potassium ferrocyanide, potassium ferricyanide, and copper(II) sulfate. Raman intensity was found to decrease with increasing particle size. The factors responsible for this trend are discussed. We conclude that the major factor is diffuse reflectance that enhances the overlap between the excitation and collection beams. The depth of sample contributing to the Raman signal has been examined for both powders and tablets as a function of powder particle size. Materials examined in this study were sodium nitrate, sodium sulfate, sodium chlorate, sodium bromate, potassium ferrocyanide, potassium ferricyanide, and copper(II) sulfate. For nonabsorbing powders, the depth of sample contributing to the signal exceeded 15 mm. The effect of the pressure used in forming tablets on the Raman signal strength and reproducibility has been examined for sodium nitrate. The Raman intensity was found to decrease with increasing pressure until a tablet of constant density was formed. The effect of particle size and particle size mismatch on the sodium nitrate Raman signal in binary mixtures with potassium chloride, potassium bromide, and potassium iodide has been examined. Good reproducibility was found to require matching of component particle sizes.
TL;DR: In this article, the authors show that the optical enhancements generated by noble metal structures can be greatly ampliµ ed in the presence of nanoscale noble metal structure, including molecular luminescence, photochemistry, molecular absorbance, optical transmission, and nonlinear processes.
Abstract: T he ef ciency of optical processes can be greatly ampli ed in the presence of nanoscale noble metal structures. Enhancement has been observed for a multitude of optical phenomena, including molecular luminescence,1–4 photochemistry,5–8 molecular absorbance,9 –12 optical transmission,13 ,14 and nonlinear processes15,16 such as second harmonic generation17,18 and hyper-Rayleigh scattering.19 ,20 Recently, the unique properties of noble metal structures have been utilized for imaging w ith sub-wavelength resolution,21–25 chemical and biological sensors,26–32 and novel photonic devices.33–41 The optical enhancements generated by noble metal structures are
TL;DR: In this article, an online detector system using laser-induced breakdown spectroscopy (LIBS) for the analysis of copper chromated arsenate (CCA) treated wood products is described.
Abstract: This paper details the design, implementation, and field evaluation of an online detector system using laser-induced breakdown spectroscopy (LIBS) for the analysis of copper chromated arsenate (CCA) treated wood products. The LIBS-based instrument functioned by creating the laser-induced plasma directly on the sample surface while wood was translated under the detector system, and was successful in discriminating between CCA treated wood and untreated wood products based on the atomic emission signal of chromium. The system was optimized for plasma emission collection both in and out of the laser focal plane and temporally optimized for chromium analysis using a compact, non-intensified charge-coupled device (CCD)/spectrometer unit. Using either single laser pulse spectra or 5-shot and 10-shot spectral averages, the accuracy of LIBS-based analysis ranged from 92 to 100% for identifying both CCA treated and untreated wood samples from the waste stream at a construction and demolition debris recycling center. Additional implementation issues are discussed in the context of LIBS-based on-line sorting of construction and demolition wood debris.
TL;DR: A detailed optimization study for laser-produced steel plasmas using time-integrated, spatially resolved emission spectroscopy in the vacuum ultraviolet (VUV) (40-160 nm) is presented in this paper.
Abstract: A detailed optimization study for laser-produced steel plasmas using time-integrated, spatially resolved emission spectroscopy in the vacuum ultraviolet (VUV) (40-160 nm) is presented. The influences of the laser focusing lens type, laser power density, laser wavelength, laser pulse energy, ambient atmospheres, and pressure, as well as spatial distribution of emitting species, on the emission characteristics of the steel plasmas are investigated. The aim of the work is to improve the detection power of the technique for the quantitative determination of carbon in solid steel alloys. In most of the work, Q-switched Nd:YAG (1064 nm, 820 mJ max. energy) laser pulses were used to create the steel plasmas. For the laser harmonics investigations, a second Q-switched Nd:YAG laser system that generated radiation at the second, third, and fourth harmonics as well as at the fundamental was employed. Air, argon, and helium were used as the surrounding atmospheres, and the pressure was varied from 0.005 mbar to 5.0 mbar depending on the gas composition. A 1 m normal incidence vacuum spectrometer, equipped with a 1200 grooves/mm concave reflective grating, was used to disperse the VUV radiation. The radiation was detected by a back-illuminated, anti-reflection coated, charge-coupled device (CCD) array detector. In general, the emission characteristics of the VUV spectral lines studied are similar to those previously investigated in the UV-visible spectral range. An unprecedented limit of detection for carbon in steels of 1.2 ± 0.2 μg/g was measured in this work.
TL;DR: In this article, the use of a reconstructed data matrix based on the significant scores and loading vectors obtained from the principal component analysis (PCA) of raw spectral data is proposed as a method to improve the data quality for 2D correlation analysis.
Abstract: The direct combination of chemometrics and two-dimensional (2D) correlation spectroscopy is considered. The use of a reconstructed data matrix based on the significant scores and loading vectors obtained from the principal component analysis (PCA) of raw spectral data is proposed as a method to improve the data quality for 2D correlation analysis. The synthetic noisy spectra were analyzed to explore the novel possibility of the use of PCA-reconstructed spectra, which are highly noise suppressed. 2D correlation analysis of this reconstructed data matrix, instead of the raw data matrix, can significantly reduce the contribution of the noise component to the resulting 2D correlation spectra.
TL;DR: In this paper, the major vibrational modes in the Stokes Raman spectra were assigned and could be attributed to the four main sugars found in the honeys, and the chemometric clustering method of discriminant function analysis indicated that the major differences between the honey samples were due to their botanical origin rather than their country of origin.
Abstract: Raman spectroscopy was investigated for its ability to discriminate between honey samples from different floral and geographical origins. The major vibrational modes in the Stokes Raman spectra were assigned and could be attributed to the four main sugars found in the honeys. The chemometric clustering method of discriminant function analysis indicated that the major differences between the honeys was due to their botanical origin rather than their country of origin, and this was confirmed by artificial neural network analyses. We consider the noninvasive nondestructive analysis of honey by Raman spectroscopy to be an alternative to the laborious and highly specialized mellisopalynology typing method currently used to identify the floral origin of honey.
TL;DR: In this paper, aqueous samples containing trace amounts of metal ions in 0.8 M HCl were ablated with an ArF laser and the signal to noise ratio was optimized when the laser fluence was about 10 J cm-2, while the detector gate delay and width were 1-2 μs and 3-4 μs, respectively.
Abstract: Aqueous samples containing trace amounts of metal ions in 0.8 M HCl were ablated with an ArF laser. Plasma emissions were monitored for elemental analysis. The signal-to-noise ratio was optimized when the laser fluence was about 10 J cm-2, while the detector gate delay and width were 1-2 μs and 3-4 μs, respectively. During that time, the temperature and electron density of the induced plasma were also measured spectroscopically. The temperature dropped from about 0.5 to about 0.3 eV, while the density remained fairly constant at about 3 × 1016 cm-3. Background-free spectrochemical analysis was therefore possible. The detection limits for Na, Ca, Ba, and Pb were 0.4, 3, 7, and 300 ppb, respectively. These are 20 to 1000 times better than the best achieved by non-193-nm laser-induced breakdown spectroscopy.