Showing papers in "Applied Spectroscopy in 2012"
TL;DR: The current state-of-the-art of analytical LIBS is summarized, providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools are discussed.
Abstract: The first part of this two-part review focused on the fundamental and diagnostics aspects of laser-induced plasmas, only touching briefly upon concepts such as sensitivity and detection limits and largely omitting any discussion of the vast panorama of the practical applications of the technique. Clearly a true LIBS community has emerged, which promises to quicken the pace of LIBS developments, applications, and implementations. With this second part, a more applied flavor is taken, and its intended goal is summarizing the current state-of-the-art of analytical LIBS, providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools. More specifically, we discuss instrumental and analytical approaches (e.g., double- and multi-pulse LIBS to improve the sensitivity), calibration-free approaches, hyphenated approaches in which techniques such as Raman and fluorescence are coupled with LIBS to increase sensitivity and information power, resonantly enhanced LIBS approaches, signal processing and optimization (e.g., signal-to-noise analysis), and finally applications. An attempt is made to provide an updated view of the role played by LIBS in the various fields, with emphasis on applications considered to be unique. We finally try to assess where LIBS is going as an analytical field, where in our opinion it should go, and what should still be done for consolidating the technique as a mature method of chemical analysis.
1,159 citations
TL;DR: The ability to obtain spatially resolved IR spectra as well as high-resolution chemical images collected at specific IR wavenumbers was demonstrated and it was shown that by taking advantage of the ability to arbitrarily control the polarization direction of the IR excitation laser, it was possible to obtain important information regarding molecular orientation in electrospun nanofibers.
Abstract: Polymer and life science applications of a technique that combines atomic force microscopy (AFM) and infrared (IR) spectroscopy to obtain nanoscale IR spectra and images are reviewed. The AFM-IR spectra generated from this technique contain the same information with respect to molecular structure as conventional IR spectroscopy measurements, allowing significant leverage of existing expertise in IR spectroscopy. The AFM-IR technique can be used to acquire IR absorption spectra and absorption images with spatial resolution on the 50 to 100 nm scale, versus the scale of many micrometers or more for conventional IR spectroscopy. In the life sciences, experiments have demonstrated the capacity to perform chemical spectroscopy at the sub-cellular level. Specifically, the AFM-IR technique provides a label-free method for mapping IR-absorbing species in biological materials. On the polymer side, AFM-IR was used to map the IR absorption properties of polymer blends, multilayer films, thin films for active devices such as organic photovoltaics, microdomains in a semicrystalline polyhydroxyalkanoate copolymer, as well as model pharmaceutical blend systems. The ability to obtain spatially resolved IR spectra as well as high-resolution chemical images collected at specific IR wavenumbers was demonstrated. Complementary measurements mapping variations in sample stiffness were also obtained by tracking changes in the cantilever contact resonance frequency. Finally, it was shown that by taking advantage of the ability to arbitrarily control the polarization direction of the IR excitation laser, it is possible to obtain important information regarding molecular orientation in electrospun nanofibers.
431 citations
TL;DR: The benefits and possibilities of using state-of-the-art hyphenated ICP-MS approaches for quantitative analysis are demonstrated with a focus on environmental and bio-analytical applications.
Abstract: This focal point review provides an overview of recent developments and capabilities of inductively coupled plasma mass spectrometry (ICP-MS) coupled with different separation techniques for applications in the fields of quantitative environmental and bio-analysis. Over the past years numerous technical improvements, which are highlighted in this review, have helped to promote the evolution of ICP-MS to one of the most versatile tools for elemental quantification. In particular, the benefits and possibilities of using state-of-the-art hyphenated ICP-MS approaches for quantitative analysis are demonstrated with a focus on environmental and bio-analytical applications.
229 citations
TL;DR: The sum of these recent advances is likely to provide unprecedented capability in measurement and scientific in-sight, which will present new opportunities for the applied spectroscopist.
Abstract: Infrared (IR) spectroscopic imaging seemingly matured as a technology in the mid-2000s, with commercially successful instrumentation and reports in numerous applications. Recent developments, however, have transformed our understanding of the recorded data, provided capability for new instrumentation, and greatly enhanced the ability to extract more useful information in less time. These developments are summarized here in three broad areas--data recording, interpretation of recorded data, and information extraction--and their critical review is employed to project emerging trends. Overall, the convergence of selected components from hardware, theory, algorithms, and applications is one trend. Instead of similar, general-purpose instrumentation, another trend is likely to be diverse and application-targeted designs of instrumentation driven by emerging component technologies. The recent renaissance in both fundamental science and instrumentation will likely spur investigations at the confluence of conventional spectroscopic analyses and optical physics for improved data interpretation. While chemometrics has dominated data processing, a trend will likely lie in the development of signal processing algorithms to optimally extract spectral and spatial information prior to conventional chemometric analyses. Finally, the sum of these recent advances is likely to provide unprecedented capability in measurement and scientific insight, which will present new opportunities for the applied spectroscopist.
224 citations
TL;DR: A quick review of the types of standoff Raman systems that are being developed and that might be suitable for astrospectroscopy, a look at specific analytes that are of interest for planetary applications, planetary measurement opportunities and challenges that need to be solved, and the feasibility of making surface and plume planetary Raman measurements from an orbiting spacecraft are discussed.
Abstract: In this review, we discuss the current state of standoff Raman spectroscopy as it applies to remote planetary applications, including standoff instrumentation, the technique's ability to identify biologically and geologically important analytes, and the feasibility to make standoff Raman measurements under various planetary conditions. This is not intended to be an exhaustive review of standoff Raman and many excellent papers are not mentioned. Rather it is intended to give the reader a quick review of the types of standoff Raman systems that are being developed and that might be suitable for astrospectroscopy, a look at specific analytes that are of interest for planetary applications, planetary measurement opportunities and challenges that need to be solved, and a brief discussion of the feasibility of making surface and plume planetary Raman measurements from an orbiting spacecraft.
108 citations
TL;DR: The results of an evaluation of the LIBS probe combined with a high-resolution spectrometer are presented and rapid detection of isotopes of uranium and hydrogen and highly enriched samples of 6Li and 7Li are demonstrated.
Abstract: The development of field-deployable instruments to monitor radiological, nuclear, and explosive (RNE) threats is of current interest for a number of assessment needs such as the on-site screening of suspect facilities and nuclear forensics. The presence of uranium and plutonium and radiological materials can be determined through monitoring the elemental emission spectrum using relatively low-resolution spectrometers. In addition, uranium compounds, explosives, and chemicals used in nuclear fuel processing (e.g., tributyl-phosphate) can be identified by applying chemometric analysis to the laser-induced breakdown (LIBS) spectrum recorded by these spectrometers. For nuclear forensic applications, however, isotopes of U and Pu and other elements (e.g., H and Li) must also be determined, requiring higher resolution spectrometers given the small magnitude of the isotope shifts for some of these elements (e.g., 25 pm for U and 13 pm for Pu). High-resolution spectrometers will be preferred for several reasons but these must fit into realistic field-based analysis scenarios. To address the need for field instrumentation, we evaluated a previously developed field-deployable hand-held LIBS interrogation probe combined with two relatively new high-resolution spectrometers (λ/∆λ ∼ 75 000 and ∼44 000) that have the potential to meet field-based analysis needs. These spectrometers are significantly smaller and lighter in weight than those previously used for isotopic analysis and one unit can provide simultaneous wide spectral coverage and high resolution in a relatively small package. The LIBS interrogation probe was developed initially for use with low resolution compact spectrometers in a person-portable backpack LIBS instrument. Here we present the results of an evaluation of the LIBS probe combined with a high-resolution spectrometer and demonstrate rapid detection of isotopes of uranium and hydrogen and highly enriched samples of 6Li and 7Li.
108 citations
TL;DR: A fully automated and model-free baseline-correction method for vibrational spectra that iteratively applies a small, but increasing, moving average window in conjunction with peak stripping to estimate spectral baselines and is suitable for the fully automated baseline correction of large numbers of spectra.
Abstract: A fully automated and model-free baseline-correction method for vibrational spectra is presented. It iteratively applies a small, but increasing, moving average window in conjunction with peak stripping to estimate spectral baselines. Peak stripping causes the area stripped from the spectrum to initially increase and then diminish as peak stripping proceeds to completion; a subsequent increase is generally indicative of the commencement of baseline stripping. Consequently, this local minimum is used as a stopping criterion. A backup is provided by a second stopping criterion based on the area under a third-order polynomial fitted to the first derivative of the current estimate of the baseline-free spectrum and also indicates whether baseline is being stripped. When the second stopping criterion is triggered instead of the first one, a proportionally scaled simulated Gaussian baseline is added to the current estimate of the baseline-free spectrum to act as an internal standard to facilitate subsequent processing and termination via the first stopping criterion. The method is conceptually simple, easy to implement, and fully automated. Good and consistent results were obtained on simulated and real Raman spectra, making it suitable for the fully automated baseline correction of large numbers of spectra.
91 citations
TL;DR: In this article, the beamline design, microscope specifications, and initial results from the new mid-infrared beamline (IRENI) are reviewed, along with future enhancements and plans for implementation of similar, small-scale instruments.
Abstract: The beamline design, microscope specifications, and initial results from the new mid-infrared beamline (IRENI) are reviewed. Synchrotron-based spectrochemical imaging, as recently implemented at the Synchrotron Radiation Center in Stoughton, Wisconsin, demonstrates the new capability to achieve diffraction limited chemical imaging across the entire mid-infrared region, simultaneously, with high signal-to-noise ratio. IRENI extracts a large swath of radiation (320 hor. × 25 vert. mrads2) to homogeneously illuminate a commercial infrared (IR) microscope equipped with an IR focal plane array (FPA) detector. Wide-field images are collected, in contrast to single-pixel imaging from the confocal geometry with raster scanning, commonly used at most synchrotron beamlines. IRENI rapidly generates high quality, high spatial resolution data. The relevant advantages (spatial oversampling, speed, sensitivity, and signal-to-noise ratio) are discussed in detail and demonstrated with examples from a variety of disciplines, including formalin-fixed and flash-frozen tissue samples, live cells, fixed cells, paint cross-sections, polymer fibers, and novel nanomaterials. The impact of Mie scattering corrections on this high quality data is shown, and first results with a grazing angle objective are presented, along with future enhancements and plans for implementation of similar, small-scale instruments.
89 citations
TL;DR: Aluminum stearate, a common paint additive, is found to influence the distribution of zinc carboxylates more strongly than pigment composition or oil type, and results in higher concentrations and more pronounced separation of saturated C16 and C18 chain zinc car boxylates in the margin of paint nearest the polyester substrate.
Abstract: Zinc oxide is a prevalent industrial-age pigment that readily reacts with fatty acids in oil-based paints to form zinc carboxylates. Zinc stearate aggregates are associated with deterioration in late nineteenth and twentieth century paintings. The current study uses both conventional and synchrotron Fourier transform infrared spectroscopy (FT-IR) to investigate metal carboxylate composition in a range of naturally aged artists' oil paints and reference paint film draw-downs. The paints contain zinc oxide alone or in combination with lead white, titanium white, and aluminum stearate and are prepared with linseed and safflower oils. Attenuated total reflectance (ATR)-FT-IR using the conventional source identifies marked differences in carboxylate profiles between exposed and protected surfaces in a large number of samples. Synchrotron FT-IR microspectroscopy of thin paint cross-sections maps metal carboxylate distributions at high spatial resolution and resolves broad concentration gradients and micrometer-scale phase separation of carboxylate species. Aluminum stearate, a common paint additive, is found to influence the distribution of zinc carboxylates more strongly than pigment composition or oil type. The presence of aluminum stearate results in higher concentrations and more pronounced separation of saturated C16 and C18 chain zinc carboxylates in the margin of paint nearest the polyester substrate. The presence of aluminum stearate in association with zinc oxide has a clear influence on zinc carboxylate formation and distribution, with potential implications for long term stability of vulnerable paintings.
84 citations
TL;DR: The LIBS spectra of tap water were recorded using the pre-concentration method and are discussed in comparison with the results from inductively coupled plasma atomic emission spectroscopy (ICP-AES).
Abstract: We report a simple sub parts per million (sub-ppm) detection method for heavy metals in water by laser-induced breakdown spectroscopy (LIBS). Filter papers were used as the substrates for both transforming aqueous solutions to solid samples and for pre-concentrating dissolved heavy metal ions. The amount of sample uptake was 1.2 g by soaking a filter paper. This provides limit-of-detection (LOD) values of 2.7 and 0.36 ppm for Pb and Cr, respectively. The LODs could be improved remarkably by pre-concentrating the heavy metal ions. When a 40 g sample solution was evaporated on a filter paper, the LODs of 75 and 18 parts per billion (ppb) were obtained for Pb and Cr, respectively. Moreover, by either increasing the evaporated amount of sample solution or applying an argon gas flow, further improvement of the LODs was found to be very promising. The LIBS spectra of tap water were recorded using the pre-concentration method and are discussed in comparison with the results from inductively coupled plasma atomic emission spectroscopy (ICP-AES). We could observe strong emission lines of Ca, Mg, K, Cu, and Sr in the tap water, of which concentrations were determined to be 6.3, 1.3, 1.1, 0.64, and 0.046 ppm, respectively, by ICP-AES. Our method shows promise as a fast, reliable, water-quality monitoring tool for heavy-metal concentrations as well as for hardness.
68 citations
TL;DR: The most widely used intensity-based biosensing assays are covered first, including nucleic acid probe-based signal amplification methods, then fluorescence lifetime, fluorescence anisotropy, and fluorescence correlation spectroscopy Assays are introduced, respectively.
Abstract: Nucleic acid fluorescent probes are playing increasingly important roles in biological sensing in recent years. In addition to the conventional functions of single-stranded DNA/RNA to hybridize with their complementary strands, affinity nucleic acids (aptamers) with specific target binding properties have also been developed, which has greatly broadened the application of nucleic acid fluorescent probes to the detection of a large variety of analytes, including small molecules, proteins, ions, and even whole cells. Another chemical property of nucleic acids is to act as substrates for various nucleic acid enzymes. This property can be utilized not only to detect those enzymes and screen their inhibitors, but also employed to develop effective signal amplification systems, which implies extensive applications. This review mainly covers the biosensing methods based on the above three types of nucleic acid fluorescent probes. The most widely used intensity-based biosensing assays are covered first, including nucleic acid probe-based signal amplification methods. Then fluorescence lifetime, fluorescence anisotropy, and fluorescence correlation spectroscopy assays are introduced, respectively. As a rapidly developing field, fluorescence imaging approaches are also briefly summarized.
TL;DR: This study suggested a direct way of determining cotton cellulose CI by calibrating XRD with the use of CIIR as references and developed a simple XRD algorithm in place of a time-consuming and subjective curve-fitting process.
Abstract: Despite considerable efforts in developing curve-fitting protocols to evaluate the crystallinity index (CI) from X-ray diffraction (XRD) measurements, in its present state XRD can only provide a qualitative or semi-quantitative assessment of the amounts of crystalline or amorphous fraction in a sample. The greatest barrier to establishing quantitative XRD is the lack of appropriate cellulose standards, which are needed to calibrate the XRD measurements. In practice, samples with known CI are very difficult to prepare or determine. In a previous study, we reported the development of a simple algorithm for determining fiber crystallinity information from Fourier transform infrared (FT-IR) spectroscopy. Hence, in this study we not only compared the fiber crystallinity information between FT-IR and XRD measurements, by developing a simple XRD algorithm in place of a time-consuming and subjective curve-fitting process, but we also suggested a direct way of determining cotton cellulose CI by calibrating XRD with the use of CI(IR) as references.
TL;DR: In this article, the authors present a review of the state-of-the-art FUV spectroscopy of liquid and solid phases in the 140-280 nm region, which they refer to as the far-UV (FUV) region.
Abstract: Ultraviolet (UV) spectroscopy has long been used together with visible (Vis) spectroscopy to investigate electronic transitions of a molecule. Most studies of the electronic structure of molecules using UV spectroscopy have been carried out in the 190-380 nm region because commercial UV-Vis spectrometers are available only for that region. The wavelength region shorter than 190 nm is also very rich in information about the electronic states and structure of a molecule, but the absorptivity is very high in this region, and thus, this region has been employed to investigate mainly the electronic states and structure of gas molecules. Because condensed-phase materials with high molecular density do not transmit much light in the shorter wavelength region of the UV, reflection spectroscopy has been used to observe spectra of solid samples in the wavelength region shorter than 190 nm. However, for liquid samples one cannot generally use either absorption spectroscopy or specular reflection spectroscopy. Accordingly, UV spectroscopy in this region for liquid samples has been a relatively undeveloped research area. To solve the above difficulties of UV spectroscopy in the wavelength region shorter than 190 nm we have recently developed a totally new UV spectrometer based on attenuated total reflection (ATR) that enables us to measure spectra of liquid and solid samples in the 140-280 nm region. We will show that spectroscopy in the wavelength region shorter than 190 nm holds considerable promise not only in basic science but also in applications such as qualitative and quantitative analysis, on-line monitoring, environmental geochemical analysis, and surface analysis. The purpose of the present review paper is to report recent progress in UV spectroscopy of solid and liquid phases in the 140-280 nm region. In this review, we refer to the 120-200 nm region to as the far-UV (FUV) region. The term “vacuum UV region” is no longer appropriate for the 120-200 nm region because most recent spectrometers used in this region are not evacuated but instead incorporate a nitrogen purge. This review consists of eight parts: (1) introduction to FUV spectroscopy, (2) brief history of FUV spectroscopy, (3) development of new FUV spectrometers, (4) FUV studies of liquid water and aqueous solutions, (5) FUV spectra of organic molecules in the liquid states, (6) band assignments by quantum chemical calculations, (7) potential applications of FUV spectroscopy in liquid and solid states; and (8) future prospects of FUV spectroscopy.
TL;DR: In this paper, laser-induced breakdown spectroscopy (LIBS) was applied to the evaluation of total element concentrations in mixtures of soils and fertilizers, and loose powder samples of these mixtures were analyzed using LIBS.
Abstract: Online analysis of nutrients in soil would be beneficial in soil and agronomic sciences as it could lead to real-time adjustment of the level of nutrients in soils. Laser-induced breakdown spectroscopy (LIBS) yields a real-time signal that could be correlated with the total elemental concentration in soils, and, hopefully, to the available fraction of the element in soils. As a first step in developing a technique for the real-time evaluation of the nutrient concentration in soils, in this study LIBS was applied to the evaluation of total element concentrations in mixtures of soils and fertilizers. Two fertilizers were mixed with soil in several concentrations, and loose powder samples of these mixtures were analyzed using LIBS. Calibration curves for three macroelements, calcium (Ca), magnesium (Mg), and phosphorus (P), and two microelements, iron (Fe) and sodium (Na), in the samples allowed determination of detection and quantification limits for total elements in soils. The correlation coefficients (r2) between total element concentrations and the LIBS signal were above 0.85 for all elements; however, we note that Ca showed evidence of self-absorption. The quantification limits were below typical total element concentration in soils; however, matrix effects demanded one calibration curve for each element and for each soil/fertilizer mixture.
TL;DR: In this article, the authors presented a standoff Raman spectra of various inorganic and organic compounds obtained from a distance of 120 m using single laser pulse excitation during daylight hours.
Abstract: The capability to analyze and detect the composition of distant samples (minerals, organics, and chemicals) in real time is of interest for various fields including detecting explosives, geological surveying, and pollution mapping. For the past 10 years, the University of Hawaii has been developing standoff Raman systems suitable for measuring Raman spectra of various chemicals in daytime or nighttime. In this article we present standoff Raman spectra of various minerals and chemicals obtained from a distance of 120 m using single laser pulse excitation during daytime. The standoff Raman system utilizes an 8-inch Meade telescope as collection optics and a frequency-doubled 532 nm Nd : YAG laser with pulse energy of 100 mJ/pulse and pulse width of 10 ns. A gated intensified charge-coupled device (ICCD) detector is used to measure time-resolved Raman spectra in daytime with detection time of 100 ns. A gate delay of 800 ns (equivalent to target placed at 120 m distance) was used to minimize interference from the atmospheric gases along the laser beam path and near-field scattering. Reproducible, good quality single-shot Raman spectra of various inorganic and organic chemicals and minerals such as ammonium nitrate, potassium perchlorate, sulfur, gypsum, calcite, benzene, nitrobenzene, etc., were obtained through sealed glass vials during daytime. The data indicate that various chemicals could easily be identified from their Raman fingerprint spectra from a far standoff distance in real time using single-shot laser excitation.
TL;DR: The development and validation of an ultraviolet (UV) spectral calibration for the prediction of tannin concentration in red wines and efficient calibration transfer to other laboratories was clearly demonstrated, with all instruments in the study effectively giving identical results on a transfer set.
Abstract: Information relating to tannin concentration in grapes and wine is not currently available simply and rapidly enough to inform decision-making by grape growers, winemakers, and wine researchers. Spectroscopy and chemometrics have been implemented for the analysis of critical grape and wine parameters and offer a possible solution for rapid tannin analysis. We report here the development and validation of an ultraviolet (UV) spectral calibration for the prediction of tannin concentration in red wines. Such spectral calibrations reduce the time and resource requirements involved in measuring tannins. A diverse calibration set (n = 204) was prepared with samples of Australian wines of five varieties (Cabernet Sauvignon, Shiraz, Merlot, Pinot Noir, and Durif), from regions spanning the wine grape growing areas of Australia, with varying climate and soils, and with vintages ranging from 1991 to 2007. The relationship between tannin measured by the methyl cellulose precipitation (MCP) reference method at 280 nm and tannin predicted with a multiple linear regression (MLR) calibration, using ultraviolet (UV) absorbance at 250, 270, 280, 290, and 315 nm, was strong (r2val = 0.92; SECV = 0.20 g/L). An independent validation set (n = 85) was predicted using the MLR algorithm developed with the calibration set and gave confidence in the ability to predict new samples, independent of the samples used to prepare the calibration (r2val = 0.94; SEP = 0.18 g/L). The MLR algorithm could also predict tannin in fermenting wines (r2val = 0.76; SEP = 0.18 g/L), but worked best from the second day of ferment on. This study also explored instrument-to-instrument transfer of a spectral calibration for MCP tannin. After slope and bias adjustments of the calibration, efficient calibration transfer to other laboratories was clearly demonstrated, with all instruments in the study effectively giving identical results on a transfer set.
TL;DR: A new compact system for time-domain diffuse optical spectroscopy of highly scattering media operating in the wavelength range from 1100 nm to 1700 nm is presented, characterized by linear behavior up to absorption values of about 3.4 cm−1.
Abstract: We present a new compact system for time-domain diffuse optical spectroscopy of highly scattering media operating in the wavelength range from 1100 nm to 1700 nm. So far, this technique has been exploited mostly up to 1100 nm: we extended the spectral range by means of a pulsed supercontinuum light source at a high repetition rate, a prism to spectrally disperse the radiation, and a time-gated InGaAs/InP single-photon avalanche diode working up to 1700 nm. A time-correlated single-photon counting board was used as processing electronics. The system is characterized by linear behavior up to absorption values of about 3.4 cm−1 where the relative error is 17%. A first measurement performed on lipids is presented: the absorption spectrum shows three major peaks at 1200 nm, 1400 nm, and 1700 nm.
TL;DR: The results illustrate the quantitative capabilities of Raman-MCR as a solvation-shell spectroscopy, including fundamental limitations arising from “intensity” and “rotational” ambiguities.
Abstract: Raman spectroscopy and multivariate curve resolution (Raman-MCR) are combined to yield a powerful spectroscopic method for identifying solute-induced perturbations of solvent molecules. The principles and applications of the resulting solvation-shell spectroscopy are described and illustrated using both numerical model spectra and experimental Raman spectra, including water in acetone and aqueous OH−, as well as of both neutral and ionic acetic acid solutions. The results illustrate the quantitative capabilities of Raman-MCR as a solvation-shell spectroscopy, including fundamental limitations arising from “intensity” and “rotational” ambiguities.
TL;DR: The rapid progress made in the applications of Raman spectroscopy to deep-ocean science is reviewed, including detection of the structure and composition of complex thermogenic gas hydrates both occurring naturally on the sea floor and in controlled sea floor experiments designed to simulate the growth of such natural systems.
Abstract: We review the rapid progress made in the applications of Raman spectroscopy to deep-ocean science. This is made possible by deployment of instrumentation on remotely operated vehicles used for providing power and data flow and for precise positioning on targets of interest. Early prototype systems have now been replaced by compact and robust units that have been deployed well over 100 times on an expeditionary basis over a very wide range of ocean depths without failure. Real-time access to the spectra obtained in the vehicle control room allows for expedition decision making. Quantification of some of the solutes in seawater or pore waters observed in the spectra is made possible by self-referencing to the ubiquitous v(2) water bending peak. The applications include detection of the structure and composition of complex thermogenic gas hydrates both occurring naturally on the sea floor and in controlled sea floor experiments designed to simulate the growth of such natural systems. New developments in the ability to probe the chemistry of sediment pore waters in situ, long thought impossible candidates for Raman study due to fluorescence observed in recovered samples, have occurred. This permits accurate measurement of the abundance of dissolved methane and sulfide in sediment pore waters. In areas where a high gas flux is observed coming out of the sediments a difference of about X30 between in situ Raman measurement and the quantity observed in recovered cores has been found. New applications under development include the ability to address deep-sea biological processes and the ability to survey the sea floor chemical conditions associated with potential sub-sea geologic CO2 disposal in abandoned oil and gas fields.
TL;DR: Raman spectroscopy with 1064 nm excitation offers advantages over alternative techniques for biomass characterization, including low spectral backgrounds, higher spectral resolution, short analysis times, and nondestructive analyses.
Abstract: Biomass representing different classes of bioenergy feedstocks, including woody and herbaceous species, was measured with 1064 nm Raman spectroscopy. Pine, oak, poplar, kenaf, miscanthus, pampas grass, switchgrass, alfalfa, orchard grass, and red clover were included in this study. Spectral differences have been identified with an emphasis on lignin guaiacyl and syringyl monomer content and carotenoid compounds. The interpretation of the Raman spectra was correlated with 13C-nuclear magnetic resonance cross-polarization/magic-angle spinning spectra of select biomass samples. Thioacidolysis quantification of guaiacyl and syringyl monomer composition and the library of Raman spectra were used as a training set to develop a principal component analysis model for classifying plant samples and a principal component regression model for quantifying lignin guaiacyl and syringyl composition. Raman spectroscopy with 1064 nm excitation offers advantages over alternative techniques for biomass characterization, including low spectral backgrounds, higher spectral resolution, short analysis times, and nondestructive analyses.
TL;DR: Optical extinction and diffuse reflection spectra of cancerous and normal prostate tissues in the 750 to 860 nm spectral range were measured and the cutoff diameter dmax of the normal tissue is larger than that of the cancerous tissue.
Abstract: Optical extinction and diffuse reflection spectra of cancerous and normal prostate tissues in the 750 to 860 nm spectral range were measured. Optical extinction measurements using thin ex vivo prostate tissue samples were used to determine the scattering coefficient (μ(s)), while diffuse reflection measurements using thick prostate tissue samples were used to extract the absorption coefficient (μ(a)) and the reduced scattering coefficient (μ'(s)). The anisotropy factor (g) was obtained using the extracted values of μ(s) and μ'(s). The values of fractal dimension (D(f)) of cancerous and normal prostate tissues were obtained by fitting to the wavelength dependence of μ'(s). The number of scattering particles contributing to μ(s) as a function of particle size and the cutoff diameter d(max) as a function of g were investigated using the fractal soft tissue model and Mie theory. Results show that d(max) of the normal tissue is larger than that of the cancerous tissue. The cutoff diameter d(max) is observed to agree with the nuclear size for the normal tissues and the nucleolar size for the cancerous tissues. Transmission spectral polarization imaging measurements were performed that could distinguish the cancerous prostate tissue samples from the normal tissue samples based on the differences between their absorption and scattering parameters.
TL;DR: It was found that the ratio of hydrogen to carbon was an important indicator of organic compounds such as uric acid and can lead to preventive therapeutic strategies and treatment methods for urological patients.
Abstract: Kidney stones were analyzed using laser-induced breakdown spectroscopy (LIBS), utilizing a high resolution multi-channel charge-coupled device (CCD) spectrometer and a nanosecond-pulse Nd : YAG laser. The kidney stones were also characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques for comparative analysis. It was found that the ratio of hydrogen (H) to carbon (C) was an important indicator of organic compounds such as uric acid. Advantages of LIBS, especially with regards to amount of sample required and sample preparation as well as the ability to carry out elemental analysis and classification of kidney stones simultaneously, over other analytical techniques such as XRD and XRF are discussed. The common minor elements detected in the kidney stones include P, S, Si, Ti, and Zn. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) of broadband LIBS spectra were employed for classifying different types of kidney stones. The results are beneficial in understanding kidney stone formation processes, which can lead to preventive therapeutic strategies and treatment methods for urological patients.
TL;DR: This paper presents a semi-blind deconvolution method to improve the spectral resolution that does not assume a known PSF but models it as a parametric function in combination with the a priori knowledge about the characteristics of the instrumental response.
Abstract: Deconvolution has become one of the most used methods for improving spectral resolution. Deconvolution is an ill-posed problem, especially when the point spread function (PSF) is unknown. Non-blind deconvolution methods use a predefined PSF, but in practice the PSF is not known exactly. Blind deconvolution methods estimate the PSF and spectrum simultaneously from the observed spectra, which become even more difficult in the presence of strong noise. In this paper, we present a semi-blind deconvolution method to improve the spectral resolution that does not assume a known PSF but models it as a parametric function in combination with the a priori knowledge about the characteristics of the instrumental response. First, we construct the energy functional, including Tikhonov regularization terms for both the spectrum and the parametric PSF. Moreover, an adaptive weighting term is devised in terms of the magnitude of the first derivative of spectral data to adjust the Tikhonov regularization for the spectrum. Then we minimize the energy functional to obtain the spectrum and the parameters of the PSF. We also discuss how to select the regularization parameters. Comparative results with other deconvolution methods on simulated degraded spectra, as well as on experimental infrared spectra, are presented.
TL;DR: In this article, the dispersion of the absolute differential Raman cross-sections of ammonium nitrate (NH4NO3), pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), nitroamine (HMX), and cyclotrimethylene-trinitramine (RDX) in acetonitrile and water solutions between 204 and 257 nm was measured.
Abstract: We measured the dispersion of the absolute-differential Raman cross-sections of ammonium nitrate (NH4NO3), pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), nitroamine (HMX), and cyclotrimethylene-trinitramine (RDX) in acetonitrile and water solutions between 204 and 257 nm. The ultraviolet (UV) resonance Raman/differential Raman cross-sections of NH4NO3, PETN, TNT, HMX, and RDX dramatically increase as the excitation wavelength decreases deep into the UV to 204 nm. NH4NO3, PETN, and RDX are best resonance-enhanced by the 204 nm excitation used here, while the optimum excitation wavelength for TNT and HMX is ∼230 nm. The excitation profile of TNT roughly follows its absorption band shape. The excitation profiles for the different Raman bands of each explosive molecule differ, indicating that multiple-excitation wavelength spectra are not redundant and can offer additional information on the species present. We see no evidence of any nonlinear spectral response or sample degradation at the fluences and spectral accumulation times used here. However, we previously observed such phenomena at longer spectral accumulation times and higher fluences. These results are promising for the development of standoff deep-UV Raman methods for explosive molecule determinations.
TL;DR: The spectroscopic approach to investigating spatial distribution of the composite components was helpful in evaluating CNC dispersion in the composite at the microscopic level, which helped explain the relatively modest reinforcement of PP by the CNCs.
Abstract: Raman spectroscopy was used to analyze cellulose nanocrystal (CNC) -polypropylene (PP) composites and to investigate the spatial distribution of CNCs in extruded composite filaments. Three composites were made from two forms of nanocellulose (CNCs from wood pulp and the nano-scale fraction of microcrystalline cellulose) and two of the three composites investigated used maleated PP as a coupling agent. Raman maps, based on cellulose and PP bands at 1098 and 1460 cm−1, respectively, obtained at 1 μm spatial resolution showed that the CNCs were aggregated to various degrees in the PP matrix. Of the three composites analyzed, two showed clear existence of phase-separated regions: Raman images with strong PP and absent/weak cellulose or vice versa. For the third composite, the situation was slightly improved but a clear transition interface between the PP-abundant and CNC-abundant regions was observed, indicating that the CNC remained poorly dispersed. The spectroscopic approach to investigating spatial distribution of the composite components was helpful in evaluating CNC dispersion in the composite at the microscopic level, which helped explain the relatively modest reinforcement of PP by the CNCs.
TL;DR: The quenching of the luminescence intensity of the UV excitonic emission due to self-absorption and multiple scattering phenomena has been investigated, pointing out the possible difficulty of detecting this signal with negative consequences in the diagnostics of works of art.
Abstract: Zinc oxide has been widely used as a white artist pigment since the end of the eighteenth century. The luminescence properties of this compound have received great interest during the last decades for promising applications in different fields of material science, but their diagnostic implications in the cultural-heritage context have been poorly exploited. This paper is intended to provide a clear picture of the luminescence behavior of zinc white in oil paintings. With this aim, three white pigments and three highly pure (analytical grade) zinc oxides were studied as powder substrates and as painting models by ultraviolet-visible (UV-VIS) fluorescence and Fourier transform infrared (FT-IR) spectroscopy. The quenching of the luminescence intensity of the UV excitonic emission due to self-absorption and multiple scattering phenomena has been investigated, pointing out the possible difficulty of detecting this signal with negative consequences in the diagnostics of works of art. By contrast, the UV emission is notably enhanced by interaction with the binder, whereas the visible emission decreases. This phenomenon is probably due to the formation of covalent bonds between zinc atoms and carboxylates from the lipidic medium that are chemisorbed on zinc oxide surfaces.
TL;DR: Silver nanoparticles were deposited spontaneously from their aqueous solution on a porous silicon (PS) layer and the morphology of the metallic layers and their SERS activity were influenced by the concentrations of the silver ion solutions used for deposition.
Abstract: Silver nanoparticles were deposited spontaneously from their aqueous solution on a porous silicon (PS) layer. The PS acts both as a reducing agent and as the substrate on which the nanoparticles nucleate. At higher silver ion concentrations, layers of nanoparticle aggregates were formed on the PS surface. The morphology of the metallic layers and their SERS activity were influenced by the concentrations of the silver ion solutions used for deposition. Raman measurements of rhodamine 6G (R6G) and crystal violet (CV) adsorbed on these surfaces showed remarkable enhancement of up to about 10 orders of magnitude.
TL;DR: The polymorphic shifts observed between α- and β-phases of this energetic material are reported and the conditions leading to the favoring of one phase over the other are discussed.
Abstract: The United States Army and the first responder community are evaluating optical detection systems for the trace detection of hazardous energetic materials. Fielded detection systems must be evaluated with the appropriate material concentrations to accurately identify the residue in theater. Trace levels of energetic materials have been observed in mutable polymorphic phases and, therefore, the systems being evaluated must be able to detect and accurately identify variant sample phases observed in spectral data. In this work, we report on the novel application of drop-on-demand technology for the fabrication of standardized trace 1,3,5-trinitro-1,3,5-triazine (RDX) samples. The drop-on-demand sample fabrication technique is compared both visually and spectrally to the more commonly used drop-and-dry technique. As the drop-on-demand technique allows for the fabrication of trace level hazard materials, concerted efforts focused on characterization of the polymorphic phase changes observed with low concentrations of RDX commonly used in drop-on-demand processing. This information is important when evaluating optical detection technologies using samples prepared with a drop-on-demand inkjet system, as the technology may be “trained” to detect the common bulk α phase of the explosive based on its spectral features but fall short in positively detecting a trace quantity of RDX (β-phase). We report the polymorphic shifts observed between α- and β-phases of this energetic material and discuss the conditions leading to the favoring of one phase over the other.
TL;DR: In this paper, the authors used infrared and Raman spectroscopy to infer the presence of the carbonate group and evaluate carbonate substitution in bioapatite structure and showed evidence for the partial replacement of [OH] by [CO3] (A-type substitution).
Abstract: We studied pathological bioapatite from patients undergoing valvular replacement due to severe aortic and mitral stenosis. Three different types of mineralized human cardiac valves were analyzed. We used infrared and Raman spectroscopy to infer the presence of the carbonate group and evaluate the carbonate substitution in bioapatite structure. The Raman spectra showed that the pathological bioapatite is a B-type “carbonate-apatite” (CO32? for PO43?) similar to the major mineralized products derived from normal biomineralization processes occurring in the human body. Fourier transform infrared spectra (FT-IR) confirmed the B-type carbonate substitution (CO32? for PO43?) and showed evidence for the partial replacement of [OH] by [CO3] (A-type substitution). The carbonate content of the samples inferred by the spectroscopic measurements is in good agreement with the range of values estimated for biological apatite. On the contrary, the crystal size of the pathological apatite estimated using the percentage area of the component at 1059 cm?1 of the infrared spectrum is in the nanometer range and it is significantly smaller than the crystal size of normal mineralized tissues.
TL;DR: Investigating the effect of experimental designs on prediction performance of quantitative models based on NIRS using a five-component formulation as a model system suggested that experimental-design selection for calibration-model development is critical, and optimum performance can be achieved with efficient experimental designs.
Abstract: Near-infrared spectroscopy (NIRS) is a valuable tool in the pharmaceutical industry, presenting opportunities for online analyses to achieve real-time assessment of intermediates and finished dosage forms. The purpose of this work was to investigate the effect of experimental designs on prediction performance of quantitative models based on NIRS using a five-component formulation as a model system. The following experimental designs were evaluated: five-level, full factorial (5-L FF); three-level, full factorial (3-L FF); central composite; I-optimal; and D-optimal. The factors for all designs were acetaminophen content and the ratio of microcrystalline cellulose to lactose monohydrate. Other constituents included croscarmellose sodium and magnesium stearate (content remained constant). Partial least squares-based models were generated using data from individual experimental designs that related acetaminophen content to spectral data. The effect of each experimental design was evaluated by determining the statistical significance of the difference in bias and standard error of the prediction for that model's prediction performance. The calibration model derived from the I-optimal design had similar prediction performance as did the model derived from the 5-L FF design, despite containing 16 fewer design points. It also outperformed all other models estimated from designs with similar or fewer numbers of samples. This suggested that experimental-design selection for calibration-model development is critical, and optimum performance can be achieved with efficient experimental designs (i.e., optimal designs).