Showing papers in "Applied Spectroscopy in 2018"
TL;DR: The technologies used in portable spectroscopy are outlined, their applications are discussed, both qualitative and quantitative, and how instrument developers and vendors have approached giving actionable answers to non-scientists are discussed.
Abstract: Until very recently, handheld spectrometers were the domain of major analytical and security instrument companies, with turnkey analyzers using spectroscopic techniques from X-ray fluorescence (XRF) for elemental analysis (metals), to Raman, mid-infrared, and near-infrared (NIR) for molecular analysis (mostly organics). However, the past few years have seen rapid changes in this landscape with the introduction of handheld laser-induced breakdown spectroscopy (LIBS), smartphone spectroscopy focusing on medical diagnostics for low-resource areas, commercial engines that a variety of companies can build up into products, hyphenated or dual technology instruments, low-cost visible-shortwave NIR instruments selling directly to the public, and, most recently, portable hyperspectral imaging instruments. Successful handheld instruments are designed to give answers to non-scientist operators; therefore, their developers have put extensive resources into reliable identification algorithms, spectroscopic libraries or databases, and qualitative and quantitative calibrations. As spectroscopic instruments become smaller and lower cost, “engines” have emerged, leading to the possibility of being incorporated in consumer devices and smart appliances, part of the Internet of Things (IOT). This review outlines the technologies used in portable spectroscopy, discusses their applications, both qualitative and quantitative, and how instrument developers and vendors have approached giving actionable answers to non-scientists. It outlines concerns on crowdsourced data, especially for heterogeneous samples, and finally looks towards the future in areas like IOT, emerging technologies for instruments, and portable hyphenated and hyperspectral instruments.
292 citations
TL;DR: This paper reviews common calibration transfer techniques, mostly related to instrument differences, and the mathematics of the uncertainty between instruments when making spectroscopic measurements of identical samples, and does not specifically address calibration maintenance or reference laboratory differences.
Abstract: Calibration transfer for use with spectroscopic instruments, particularly for near-infrared, infrared, and Raman analysis, has been the subject of multiple articles, research papers, book chapters, and technical reviews. There has been a myriad of approaches published and claims made for resolving the problems associated with transferring calibrations; however, the capability of attaining identical results over time from two or more instruments using an identical calibration still eludes technologists. Calibration transfer, in a precise definition, refers to a series of analytical approaches or chemometric techniques used to attempt to apply a single spectral database, and the calibration model developed using that database, for two or more instruments, with statistically retained accuracy and precision. Ideally, one would develop a single calibration for any particular application, and move it indiscriminately across instruments and achieve identical analysis or prediction results. There are many technical aspects involved in such precision calibration transfer, related to the measuring instrument reproducibility and repeatability, the reference chemical values used for the calibration, the multivariate mathematics used for calibration, and sample presentation repeatability and reproducibility. Ideally, a multivariate model developed on a single instrument would provide a statistically identical analysis when used on other instruments following transfer. This paper reviews common calibration transfer techniques, mostly related to instrument differences, and the mathematics of the uncertainty between instruments when making spectroscopic measurements of identical samples. It does not specifically address calibration maintenance or reference laboratory differences.
122 citations
TL;DR: Recent developments that demonstrate potential for point of care impact and major trends in spectroscopic analyses ranging from in vivo measurements to that of ex vivo bodily fluids to extracted and processed tissues are provided.
Abstract: Vibrational spectroscopy and imaging promise molecular information that can be rapidly acquired without the need for specialized stains or dyes, thereby potentially simplifying and speeding up necessary analyses for interventions in many facets of modern day healthcare. The salient characteristics of vibrational spectroscopy for molecular analyses, using non-perturbative optical measurements, and employing computational analysis of data, are especially useful near the point of care as assessments can be made with fewer reagents, under pressure of time and accuracy while not requiring extensive specialized human expertise. Significant technological development has occurred and many seminal proof of concept studies have been conducted to demonstrate the utility and vast potential of spectroscopic methods. Accordingly, a number of studies have focused on pushing the fundamental performance limits of spectroscopic methods while others have focused on specific problems where the use of vibrational spectroscopy promises to change the standard of care. Despite this impressive progress, however, the application area is still maturing and rapidly evolving. A vast array of potential applications continues to be assessed while others need further technological developments. In this review, we focus on recent developments that demonstrate potential for point of care impact and major trends that can lead, in turn, to improved spectroscopic technology. We provide focused examples of ‘‘case studies’’ and major trends in spectroscopic analyses ranging from in vivo measurements to that of ex vivo bodily fluids to extracted and processed tissues. In each case, the uniting theme is that information to the clinician is enabled closer to the patient, allowing for a shorter time between identification of the need for analyses and availability of information that guides care. Raman Spectroscopy for Intraoperative and In Vivo Diagnostics
79 citations
TL;DR: This review provided a systematic outline of the historical development of LSFM, detailed discussion on the variants and improvements of LsfM, and delineation on the most recent technological advancements of L SFM and its potential applications in single molecule/particle detection, single-molecule super-resolution imaging, imaging intracellular dynamics of a single cell, multicellular imaging.
Abstract: The introduction of light sheet fluorescence microscopy (LSFM) has overcome the challenges in conventional optical microscopy. Among the recent breakthroughs in fluorescence microscopy, LSFM had been proven to provide a high three-dimensional spatial resolution, high signal-to-noise ratio, fast imaging acquisition rate, and minuscule levels of phototoxic and photodamage effects. The aforementioned auspicious properties are crucial in the biomedical and clinical research fields, covering a broad range of applications: from the super-resolution imaging of intracellular dynamics in a single cell to the high spatiotemporal resolution imaging of developmental dynamics in an entirely large organism. In this review, we provided a systematic outline of the historical development of LSFM, detailed discussion on the variants and improvements of LSFM, and delineation on the most recent technological advancements of LSFM and its potential applications in single molecule/particle detection, single-molecule super-resolution imaging, imaging intracellular dynamics of a single cell, multicellular imaging: cell-cell and cell-matrix interactions, plant developmental biology, and brain imaging and developmental biology.
51 citations
TL;DR: The current trends and future prospects of integrating Raman/SERS-isotopic labeling and cell sorting technologies in parallel are summarized, to link genotype-to-phenotype in order to define community function of unculturable microbial cells in mixed microbial communities which possess admirable traits such as detoxification of pollutants and recycling of essential metals.
Abstract: The microbial world forms a huge family of organisms that exhibit the greatest phylogenetic diversity on Earth and thus colonize virtually our entire planet. Due to this diversity and subsequent complex interactions, the vast majority of microorganisms are involved in innumerable natural bioprocesses and contribute an absolutely vital role toward the maintenance of life on Earth, whilst a small minority cause various infectious diseases. The ever-increasing demand for environmental monitoring, sustainable ecosystems, food security, and improved healthcare systems drives the continuous search for inexpensive but reproducible, automated and portable techniques for detection of microbial isolates and understanding their interactions for clinical, environmental, and industrial applications and benefits. Surface-enhanced Raman scattering (SERS) is attracting significant attention for the accurate identification, discrimination and characterization and functional assessment of microbial cells at the single cell level. In this review, we briefly discuss the technological advances in Raman and Fourier transform infrared (FT-IR) instrumentation and their application for the analysis of clinically and industrially relevant microorganisms, biofilms, and biological warfare agents. In addition, we summarize the current trends and future prospects of integrating Raman/SERS-isotopic labeling and cell sorting technologies in parallel, to link genotype-to-phenotype in order to define community function of unculturable microbial cells in mixed microbial communities which possess admirable traits such as detoxification of pollutants and recycling of essential metals.
51 citations
TL;DR: Fluorescence spectroscopy combined with chemometrics showed its robustness to identify and quantify the specified adulterant in pure EVOO.
Abstract: Due to high price and nutritional values of extra virgin olive oil (EVOO), it is vulnerable to adulteration internationally. Refined oil or other vegetable oils are commonly blended with EVOO and t...
45 citations
TL;DR: The SIMCA analysis provides a suitable analytical tool for the correct assignment of the type of polymer on the basis of the NIR spectra measured with the handheld spectrometers, and shows that the five polymer commodities cluster in the score plots of their first three principal components (PCs).
Abstract: For sustainable utilization of raw materials and environmental protection, the recycling of the most common polymers—polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvin...
43 citations
TL;DR: A rapid coal analyzer based on laser-induced breakdown spectroscopy (LIBS) was developed for rapid quality analysis of pulverized coal and it is shown that it is capable of performing reliable and accurate analysis of coal quality.
Abstract: Determination of coal quality plays a major role in coal-fired power plants and coal producers for optimizing the utilization efficiency and controlling the quality. In this work, a rapid coal analyzer based on laser-induced breakdown spectroscopy (LIBS) was developed for rapid quality analysis of pulverized coal. The structure of the LIBS apparatus was introduced in detail. To avoid time-consuming and complicated sample preparation, a pulverized feeding machine was designed to form a continuously stable coal particle flow. The standard deviation (SD) of characteristic peaks was used to estimate the spectral valid data in this experiment. Coupled with cluster analysis, artificial neural networks and genetic algorithm are employed as a nonlinear regression method in order to indicate the relationship between coal quality and the corresponding plasma spectra. It is shown that the average absolute error of ash, volatile matter, fixed carbon, and gross calorific value for the validation set is 0.82%, 0.85%, 0.96%, and 0.48 MJ/kg. The average standard deviation of repeated samples is 1.64%, 0.92%, 1.08%, and 0.86 MJ/kg, showing a high sample-to-sample repeatability. This rapid coal analyzer is capable of performing reliable and accurate analysis of coal quality.
43 citations
TL;DR: The employed SC source operates in the spectral region of 1.2–4.6 µm, filling the spectral gap where quantum cascade lasers lack broader availability and the real-time capability of the setup is demonstrated by monitoring the evaporation of liquid 2-propanol.
Abstract: Mid-infrared (MIR) supercontinuum (SC) lasers are an attractive new option in the field of IR spectroscopy, especially for standoff detection. Supercontinuum radiation unites high brightness, high ...
41 citations
TL;DR: This viewpoint focuses on the key features that contributed to the influential, problem-solving character of LIBS and discusses current achievements in standoff LIBS methods, underwater solids inspection, and single nanoparticle analysis.
Abstract: Laser-induced breakdown spectroscopy (LIBS) is currently considered one of the most active research areas in the field of analytical spectroscopy. Over the years, scientists and engineers have focused on the development of LIBS as a tool for chemical measurements, with significant efforts in developing new devices, methods, and data processing algorithms to improve the analytical performance of LIBS. In combination with tailored excitation methods using multipulse, multiwavelength laser systems, substantial improvements in detection power, representativeness, accuracy, and sampling throughput have been achieved. Development of LIBS instruments with extended capabilities for energy delivery to the sample using ultrashort laser pulses has been undertaken, which has permitted a better understanding of the underlying issues of LIBS; notably, laser interaction with matter, plasma dynamics, and properties. As a result, LIBS has emerged as a powerful alternative for chemical analysis in a wide front of applications, from geological exploration to industrial inspection, from environmental monitoring to biomedical and forensic analysis, from cultural heritage to homeland security. While LIBS certainly has practical utility in many laboratory-based chemical measurements, the true potential of this technology becomes apparent when it is used for applications inaccessible to more conventional analytical techniques. Inspection of the elemental composition of distant objects and LIBS analysis underwater solids constitute examples of the exclusive capabilities of LIBS. Since detailed account of plasma fundamentals, instruments, methods and applications of LIBS can be found in the extensive literature on the topic, this viewpoint focuses on the key features that contributed to the influential, problem-solving character of LIBS. We take the perspective of our own work in the field and discuss current achievements in standoff LIBS methods, underwater solids inspection, and single nanoparticle analysis. We then introduce the strategies used for improving the detection power of LIBS and discuss the use of LIBS in combination with other spectroscopic tools. Finally, we identify challenges that merit further attention, by underlining some possible ways to solve the most common impediments for advancement of LIBS towards an enabling analytical technology. Standoff LIBS
41 citations
TL;DR: The results showed the potential of using a NIR portable spectrophotometer combined with a ML approach for differentiation of chicken parts in the processing industry.
Abstract: Identification of different chicken parts using portable equipment could provide useful information for the processing industry and also for authentication purposes. Traditionally, physical–chemica...
TL;DR: A comparison between the values of model parameters of solutions with BSA and without BSA allowed to conclude that the main effect of BSA is the formation of strongly bound hydration shells in the immediate proximity to the protein molecule.
Abstract: Terahertz time-domain spectroscopy (THz-TDS) was used to determine the spectra (range = 1.2–120 cm−1) of aqueous solutions of bovine serum albumin (BSA) at pH range 2.5–10. Under each of the selected pH, BSA molecules exist in a different conformation, compared to other pH values. The spectra were used to calculate the functions of the dielectric permittivity of BSA solutions. Dielectric functions of the aqueous phase of BSA solutions were calculated based on the Bruggeman model, without the contribution of BSA itself. Fitting of the dielectric functions was performed using a model which includes three water spectral bands: two relaxation bands with relaxation times of about 8.28 and 0.3 ps and a vibrational band with a maximum of about 180 cm−1. The parameters of these bands were determined through fitting and physical interpretation at the molecular level can be provided for each of them. A comparison between the values of model parameters of solutions with BSA and without BSA allowed to conclude that the main effect of BSA is the formation of strongly bound hydration shells in the immediate proximity to the protein molecule. At the same time, the structure of more distant layers of the hydration shells is destroyed, with an increased formation of free water molecules. Some differences are observed in the effect of different BSA conformations on the aqueous phase of solution. The proposed approach can be generalized and applied for studying of a wide class of biological macromolecules in aqueous solutions.
TL;DR: In this article, the effect of perturbations to the spectrum from atomic and molecular line processes on the spectrum of the sky-averaged intensity spectrum has been examined, and the current status of the understanding of the cosmic background from radio to γ-ray energies has been discussed.
Abstract: Cosmic background (CB) radiation, encompassing the sum of emission from all sources outside our own Milky Way galaxy across the entire electromagnetic spectrum, is a fundamental phenomenon in observational cosmology. Many experiments have been conceived to measure it (or its constituents) since the extragalactic Universe was first discovered; in addition to estimating the bulk (cosmic monopole) spectrum, directional variations have also been detected over a wide range of wavelengths. Here we gather the most recent of these measurements and discuss the current status of our understanding of the CB from radio to γ-ray energies. Using available data in the literature, we piece together the sky-averaged intensity spectrum and discuss the emission processes responsible for what is observed. We examine the effect of perturbations to the continuum spectrum from atomic and molecular line processes and comment on the detectability of these signals. We also discuss how one could, in principle, obtain a complete census of the CB by measuring the full spectrum of each spherical harmonic expansion coefficient. This set of spectra of multipole moments effectively encodes the entire statistical history of nuclear, atomic, and molecular processes in the Universe.
TL;DR: Analysis of unknown samples indicated that the prediction results of these samples were found comparable to those obtained by inductively coupled plasma mass spectrometry analysis, suggesting that LIBS has potential to quantify REEs in geological minerals/ores.
Abstract: Laser-induced breakdown spectroscopy (LIBS) was used to detect rare earth elements (REEs) in natural geological samples. Low and high intensity emission lines of Ce, La, Nd, Y, Pr, Sm, Eu, Gd, and Dy were identified in the spectra recorded from the samples to claim the presence of these REEs. Multivariate analysis was executed by developing partial least squares regression (PLS-R) models for the quantification of Ce, La, and Nd. Analysis of unknown samples indicated that the prediction results of these samples were found comparable to those obtained by inductively coupled plasma mass spectrometry analysis. Data support that LIBS has potential to quantify REEs in geological minerals/ores.
TL;DR: This work reviews recent progress and perspectives in the nanoscale analysis of anisotropic materials using an extended version of the atomic force microscopy–infrared (AFM-IR) technique, which includes polarization control of the incoming light and bridges the gap in IR spectroscopic analysis of local anisotrop material properties.
Abstract: Infrared techniques enable nondestructive and label-free studies of thin films with high chemical and structural contrast. In this work, we review recent progress and perspectives in the nanoscale analysis of anisotropic materials using an extended version of the atomic force microscopy-infrared (AFM-IR) technique. This advanced photothermal technique, includes polarization control of the incoming light and bridges the gap in IR spectroscopic analysis of local anisotropic material properties. Such local anisotropy occurs in a wide range of materials during molecular nucleation, aggregation, and crystallization processes. However, analysis of the anisotropy in morphology and structure can be experimentally and theoretically demanding as it is related to order and disorder processes in ranges from nanoscopic to macroscopic length scales, depending on preparation and environmental conditions. In this context IR techniques can significantly assist as IR spectra can be interpreted in the framework of optical models and numerical calculations with respect to both, the present chemical conditions as well as the micro- and nanostructure. With these extraordinary analytic possibilities, the advanced AFM-IR approach is an essential puzzle piece in direction to connect nanoscale and macroscale anisotropic thin film properties experimentally. In this review, we highlight the analytic possibilities of AFM-IR for studies on nanoscale anisotropy with a set of examples for polymer, plasmonic, and polaritonic films, as well as aggregates of large molecules and proteins.
TL;DR: It was determined that the HH LIBS method was able to clearly discern the rare earths elements of interest in the glass or uranium matrices, and demonstrates the ability to rapidly identify elemental constituents in sub-percent levels in a uranium matrix.
Abstract: A portable handheld laser-induced breakdown spectroscopy (HH LIBS) instrument was evaluated as a rapid method to qualitatively analyze rare earth elements in a uranium oxide matrix. This research is motivated by the need for development of a method to perform rapid, at-line chemical analysis in a nuclear facility, particularly to provide a rapid first pass analysis to determine if additional actions or measurements are warranted. This will result in the minimization of handling and transport of radiological and nuclear material and subsequent exposure to their associated hazards. In this work, rare earth elements (Eu, Nd, and Yb) were quantitatively spiked into a uranium oxide powder and analyzed by the HH LIBS instrumentation. This method demonstrates the ability to rapidly identify elemental constituents in sub-percent levels in a uranium matrix. Preliminary limits of detection (LODs) were determined with values on the order of hundredths of a percent. Validity of this methodology was explored by employing a National Institute of Standards and Technology (NIST) standard reference materials (SRM) 610 and 612 (Trace Elements in Glass). It was determined that the HH LIBS method was able to clearly discern the rare earths elements of interest in the glass or uranium matrices.
TL;DR: A CF-LIBS quantitative analysis method based on the auto-selection of internal reference line and the optimized estimation of plasma temperature and the promising potential of in situ and real-time application is proposed.
Abstract: The quantitative analysis accuracy of calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is severely affected by the self-absorption effect and estimation of plasma temperature. Herein, a CF-LIBS quantitative analysis method based on the auto-selection of internal reference line and the optimized estimation of plasma temperature is proposed. The internal reference line of each species is automatically selected from analytical lines by a programmable procedure through easily accessible parameters. Furthermore, the self-absorption effect of the internal reference line is considered during the correction procedure. To improve the analysis accuracy of CF-LIBS, the particle swarm optimization (PSO) algorithm is introduced to estimate the plasma temperature based on the calculation results from the Boltzmann plot. Thereafter, the species concentrations of a sample can be calculated according to the classical CF-LIBS method. A total of 15 certified alloy steel standard samples of known compositions and elemental weight percentages were used in the experiment. Using the proposed method, the average relative errors of Cr, Ni, and Fe calculated concentrations were 4.40%, 6.81%, and 2.29%, respectively. The quantitative results demonstrated an improvement compared with the classical CF-LIBS method and the promising potential of in situ and real-time application.
TL;DR: Original approaches by which transmission Fourier transform infrared, attenuated total reflection (ATR) FT-IR, and Raman spectroscopy can be confidently used to quantify bone mineral crystallinity are described and recommended.
Abstract: Bone mineral crystallinity is an important factor determining bone quality and strength. The gold standard method to quantify crystallinity is X-ray diffraction (XRD), but vibrational spectroscopic...
TL;DR: An automated baseline correction method based on iterative morphological operations that can adaptively determine the structuring element first and then gradually remove the spectral peaks during iteration to get an estimated baseline is proposed.
Abstract: Raman spectra usually suffer from baseline drift caused by fluorescence or other reasons. Therefore, baseline correction is a necessary and crucial step that must be performed before subsequent processing and analysis of Raman spectra. An automated baseline correction method based on iterative morphological operations is proposed in this work. The method can adaptively determine the structuring element first and then gradually remove the spectral peaks during iteration to get an estimated baseline. Experiments on simulated data and real-world Raman data show that the proposed method is accurate, fast, and flexible for handling different kinds of baselines in various practical situations. The comparison of the proposed method with some state-of-the-art baseline correction methods demonstrates its advantages over the existing methods in terms of accuracy, adaptability, and flexibility. Although only Raman spectra are investigated in this paper, the proposed method is hopefully to be used for the baseline correction of other analytical instrumental signals, such as IR spectra and chromatograms.
TL;DR: The use of dual-domain regression models, which were built utilizing a wavelet prism decomposition and paired with transfer by orthogonal projection, for the calibration transfer of near-infrared (NIR) spectra are reported.
Abstract: We report the use of dual-domain regression models, which were built utilizing a wavelet prism decomposition and paired with transfer by orthogonal projection, for the calibration transfer of near-infrared (NIR) spectra. The new method is based on obtaining specific frequency components for a spectrum via wavelet analysis, projecting the frequency components of the primary instrument onto the subspace orthogonal to the mean instrumental difference between spectra from the primary and the secondary instrument, and weighting each frequency component model according to the cross-validation error of the frequency components of the projected primary instrument's spectra to generate a stacked ensemble model robust to contributions to the spectra from instrumental variations. The method, which does not require property values from the secondary data set, is tested on three NIR data sets, and is compared with orthogonal projection in the wavelength domain, orthogonal signal correction, and with model updating approaches. For the data sets we examined, we show that the prediction performance of the new method is competitive with orthogonal projections in the wavelength domain, as well as orthogonal signal correction and model updating approaches, both of which require property values for spectra from the secondary instrument. Examination of the spectral data reconstructed from the projected frequency components indicates that aspects of the data that may be attributable to instrumental or physical phenomena (i.e., instrumental baseline shifts or discretized intensity changes which may be attributed to scatter) are suppressed, but those associated with the chemical phenomena are retained. The benefits of orthogonal projection on each individual frequency component are further corroborated by the fact that the models based on frequency component projection generalize better to unseen instruments compared with the other methods.
TL;DR: Results show that SHRS does have the ability of in situ analysis or standoff detection for simulants of CWAs, and the potential feasibility of standoff detection of SHRS for CWAs simulants has been proved.
Abstract: Raman spectroscopic detection is one of the suitable methods for the detection of chemical warfare agents (CWAs) and simulants. Since the 1980s, many researchers have been dedicated to the research of chemical characteristic of CWAs and simulants and instrumental improvement for their analysis and detection. The spatial heterodyne Raman spectrometer (SHRS) is a new developing instrument for Raman detection that appeared in 2011. It is already well-known that SHRS has the characteristics of high spectral resolution, a large field-of-view, and high throughput. Thus, it is inherently suitable for the analysis and detection of these toxic chemicals and simulants. The in situ and standoff detection of some typical simulants of CWAs, such as dimethyl methylphosphonate (DMMP), diisopropyl methylphosphonate (DIMP), triethylphosphate (TEP), diethyl malonate (DEM), methyl salicylate (MES), 2-chloroethyl ethyl sulfide (CEES), and malathion, were tried. The achieved results show that SHRS does have the ability of in situ analysis or standoff detection for simulants of CWAs. When the laser power was set to as low as 26 mW, the SHRS still has a signal-to-noise ratio higher than 5 in in situ detection. The standoff Raman spectra detection of CWAs simulants was realized at a distance of 11 m. The potential feasibility of standoff detection of SHRS for CWAs simulants has been proved.
TL;DR: The aerosol-LIBS system performed well in monitoring the U concentration and it is expected that the system could be used to quantitatively determine the U compositions within the normal operational concentrations of U in pyroprocessing molten salts.
Abstract: In this current study, the molten salt aerosol-laser-induced breakdown spectroscopy (LIBS) system was used to measure the uranium (U) content in a ternary UCl3-LiCl-KCl salt to investigate and assess a near real-time analytical approach for material safeguards and accountability. Experiments were conducted using five different U concentrations to determine the analytical figures of merit for the system with respect to U. In the analysis, three U lines were used to develop univariate calibration curves at the 367.01 nm, 385.96 nm, and 387.10 nm lines. The 367.01 nm line had the lowest limit of detection (LOD) of 0.065 wt% U. The 385.96 nm line had the best root mean square error of cross-validation (RMSECV) of 0.20 wt% U. In addition to the univariate calibration approach, a multivariate partial least squares (PLS) model was developed to further analyze the data. Using partial least squares (PLS) modeling, an RMSECV of 0.085 wt% U was determined. The RMSECV from the multivariate approach was significantly better than the univariate case and the PLS model is recommended for future LIBS analysis. Overall, the aerosol-LIBS system performed well in monitoring the U concentration and it is expected that the system could be used to quantitatively determine the U compositions within the normal operational concentrations of U in pyroprocessing molten salts.
TL;DR: A correlation-based SPA (CB-SPA) is proposed to apply the successive projections algorithm in regions with consistent correlation and the result shows that CB-SPA can select variable subsets with more valuable variables and less multi-collinearity.
Abstract: Near-infrared spectroscopy is an efficient, low-cost technology that has potential as an accurate method in detecting the nitrogen content of natural rubber leaves. Successive projections algorithm (SPA) is a widely used variable selection method for multivariate calibration, which uses projection operations to select a variable subset with minimum multi-collinearity. However, due to the fluctuation of correlation between variables, high collinearity may still exist in non-adjacent variables of subset obtained by basic SPA. Based on analysis to the correlation matrix of the spectra data, this paper proposed a correlation-based SPA (CB-SPA) to apply the successive projections algorithm in regions with consistent correlation. The result shows that CB-SPA can select variable subsets with more valuable variables and less multi-collinearity. Meanwhile, models established by the CB-SPA subset outperform basic SPA subsets in predicting nitrogen content in terms of both cross-validation and external prediction. Moreover, CB-SPA is assured to be more efficient, for the time cost in its selection procedure is one-twelfth that of the basic SPA.
TL;DR: Univariate and multivariate statistical analysis methods showed that the contents of major mineral elements were higher in lactose-free dairy milk than those in dairy milk.
Abstract: Laser-induced breakdown spectroscopy (LIBS) technique was used to compare various types of commercial milk products. Laser-induced breakdown spectroscopy spectra were investigated for the determination of the elemental composition of soy and rice milk powder, dairy milk, and lactose-free dairy milk. The analysis was performed using radiative transitions. Atomic emissions from Ca, K, Na, and Mg lines observed in LIBS spectra of dairy milk were compared. In addition, proteins and fat level in milks can be determined using molecular emissions such as CN bands. Ca concentrations were calculated to be 2.165 ± 0.203 g/L in 1% of dairy milk fat samples and 2.809 ± 0.172 g/L in 2% of dairy milk fat samples using the standard addition method (SAM) with LIBS spectra. Univariate and multivariate statistical analysis methods showed that the contents of major mineral elements were higher in lactose-free dairy milk than those in dairy milk. The principal component analysis (PCA) method was used to discriminate four milk samples depending on their mineral elements concentration. In addition, proteins and fat level in dairy milks were determined using molecular emissions such as CN band. We applied partial least squares regression (PLSR) and simple linear regression (SLR) models to predict levels of milk fat in dairy milk samples. The PLSR model was successfully used to predict levels of milk fat in dairy milk sample with the relative accuracy (RA%) less than 6.62% using CN (0,0) band.
TL;DR: The resulting OB-CD2 strategy is shown to more accurately estimate Raman scattering rates of each chemical component, when compared to the original OB- CD, thus facilitating chemical classification at speeds as fast as 3 μs per measurement and the collection of Raman images in under a second.
Abstract: The previously described optimized binary compressive detection (OB-CD) strategy enables fast hyperspectral Raman (and fluorescence) spectroscopic analysis of systems containing two or more chemical components. However, each OB-CD filter collects only a fraction of the scattered photons and the remainder of the photons are lost. Here, we present a refinement of OB-CD, the OB-CD2 strategy, in which all of the collected Raman photons are detected using a pair of complementary binary optical filters that direct photons of different colors to two photon counting detectors. The OB-CD2 filters are generated using a new optimization algorithm described in this work and implemented using a holographic volume diffraction grating and a digital micromirror device (DMD) whose mirrors are programed to selectively direct photons of different colors either to one or the other photon-counting detector. When applied to pairs of pure liquids or two-component solid powder mixtures, the resulting OB-CD2 strategy is shown to more accurately estimate Raman scattering rates of each chemical component, when compared to the original OB-CD, thus facilitating chemical classification at speeds as fast as 3 μs per measurement and the collection of Raman images in under a second.
TL;DR: The results indicate that water structure is sensitive to temperature and the oligopeptide in aqueous solution improves the thermal stability of the water species.
Abstract: Investigating the interaction between oligopeptide and water is essential for understanding the structure, dynamics and function of proteins. Temperature-dependent near-infrared (NIR) spectroscopy and independent component analysis (ICA) were employed to study the interaction between oligopeptide and water in aqueous solution. The NIR spectra of two homo-oligopeptides, penta-aspartic acid (D5) and penta-lysine (K5), in aqueous solution of different concentration were measured at different temperature (30-90 ℃). Independent component analysis was performed to extract the spectral information that changes with temperature. The independent components (ICs) representing the spectral information of NH and CH2 groups were obtained. Compared with D5, the two groups in K5 change significantly at higher temperature. The result may suggest that K5 has stronger interaction with water than D5. Moreover, three ICs that contain the spectral information of the water species with no (S0), one (S1), and two (S2) hydrogen-bonds were obtained. It was shown that the spectral intensity of S0 and S1 increases while that of S2 decreases with the temperature, and the changes of oligopeptide solutions are weaker than those of pure water. The results indicate that water structure is sensitive to temperature and the oligopeptide in aqueous solution improves the thermal stability of the water species. When oligopeptide is added, the spectral intensity of S0 and S2 decreases and that of S1 increases for D5 solution, but the intensity of all the three species decreases for K5 solution. Furthermore, the concentration effect of K5 was found to be stronger than D5. The result may reveal that D5 combines with water molecule through forming one hydrogen bond but K5 interacts with water through a different way.
TL;DR: A novel algorithm based on wavelet transform that contains denoising and baseline correction is presented to automatically extract Raman signals, and it is noteworthy that this algorithm requires few human interventions, which enables automatic denoisation and background removal.
Abstract: Noise and fluorescent background are two major problems for acquiring Raman spectra from samples, which blur Raman spectra and make Raman detection or imaging difficult. In this paper, a novel algorithm based on wavelet transform that contains denoising and baseline correction is presented to automatically extract Raman signals. For the denoising section, the improved conventional-scale correlation denoising method is proposed. The baseline correction section, which is performed after denoising, basically consists of five aspects: (1) detection of the peak position; (2) approximate second derivative calculation based on continuous wavelet transform is performed using the Haar wavelet function to find peaks and background areas; (3) the threshold is estimated from the peak intensive area for identification of peaks; (4) correction of endpoints, spectral peaks, and peak position; and (5) determine the endpoints of the peak after subtracting the background. We tested this algorithm for simulated and experimental Raman spectra, and a satisfactory denoising effect and a good capability to correct background are observed. It is noteworthy that this algorithm requires few human interventions, which enables automatic denoising and background removal.
TL;DR: In this article, the effects of thermal boundary layers on tunable diode laser absorption spectroscopy (TDLAS) measurement results were quantified when using the line-of-sight (LOS) TDLAS under conditions with s...
Abstract: The effects of thermal boundary layers on tunable diode laser absorption spectroscopy (TDLAS) measurement results must be quantified when using the line-of-sight (LOS) TDLAS under conditions with s...
TL;DR: It is concluded that for unpolished samples, laser Raman microprobe analysis is most effective as a means of identifying pyrite, and the presence of solid solution therein, when laser power is low enough to avoid substantial heating.
Abstract: Two probable causes of variability in the Raman spectrum of unpolished pyrite are well recognized, in principle, but not always in practice, namely: (1) downshifting of band positions due to laser heating; and (2) variations in the ratios of band intensities due to crystallographic orientation of the sample with respect to the laser's dominant polarization plane. The aims of this paper are to determine whether these variations can be used to acquire additional information about pyrites. Here, using laser Raman microprobe analysis of natural, unpolished pyrite samples, we investigate the magnitude of downshifting of band positions associated with laser heating of different sizes of pyrite grains. We demonstrate that the magnitude of this effect can be large (up to ∼10 cm-1), negatively proportional to grain size, of greater magnitude than the effect typically attributable to natural intersample differences in trace element (TE) solid solution, and of similar magnitude among bands. Through Raman analysis of naturally occurring faces on pyrite samples at various angles of rotation, we also demonstrate that the three most common faces on pyrite can be distinguished by the ratio of the intensities of the dominant bands. We conclude that for unpolished samples, laser Raman microprobe analysis is most effective as a means of identifying pyrite, and the presence of solid solution therein, when laser power is low enough to avoid substantial heating. Once pyrite has been identified, higher laser powers can be used to produce spectra whose ratios of band intensities indicate the face or crystallographic plane being irradiated.
TL;DR: This paper reports the use of laboratory methods that measure the IR hemispherical reflectance of solids using an integrating sphere and have applied it to the identification of mineral mixtures, with widely varying percentages of uranium mineral content.
Abstract: The identification of minerals, including uranium-bearing species, is often a labor-intensive process using X-ray diffraction (XRD), fluorescence, or other solid-phase or wet chemical techniques. W...