Evaluation of portable Raman spectrometer with 1064 nm excitation for geological and forensic applications

A Raman spectroscopy based chemometric approach to predict the derived cetane number of hydrocarbon jet fuels and their mixtures

Fuel ignition quality, measured in the form of Derived Cetane Number (DCN), is an important part of integrating fuels, including sustainable aviation fuels, in compression ignition engines. DCN has been correlated with simulated and/or real spectroscopic measurements as well as other physical and chemical properties, but rarely have these correlations developed into a pathway to application. One application of the correlations is the use of miniaturized onboard fuel sensors that could assist, by using predicted DCN, in real-time feedforward engine control. To aid in the application of developing such DCN fuel sensors, Raman spectra coupled with chemometrics and a selection of influential spectral features were investigated. In this study, the Raman spectra were obtained from a database that included jet fuels, jet fuel mixtures, pure hydrocarbon components, and their weighted mixtures. The resulting Raman spectral database from the experimental measurements included spectra of components that span a wide range of DCNs and covered all the expected chemical functional groups present in a standard jet fuel. Chemometric models were developed to associate Raman spectra with DCN in subsets of the spectral range to aid in sensor miniaturization. The models were tested on jet fuels such as National Jet Fuel Combustion Program fuels designated A-1, A-2, and A-3 along with mixtures of jet fuels that spanned a wide range of DCN, simulating fuels that could represent real-world scenarios. An Artificial Neural Network (ANN) model trained on the fingerprint region (500 cm-1 - 1800 cm-1) of the Raman spectra was able to capture the non-linearity of the association between the Raman spectra and DCN with a test R2 score of 0.926, a test MSE of 3.61, and a test MPE of 3.41. Around 97 % of the unseen test samples were predicted within 10 % of the DCN measured with an Ignition Quality Tester. One hundred features of the fingerprint region influencing DCN predictions in the optimal ANN model were extracted using a Global Surrogate (GS) model. A reduced ANN model trained on only these one hundred features performed slightly better with a test R2 score of 0.935, test MSE of 3.19, test MPE of 3.20 and with the entire set of unseen test samples predicted within 10 % of the measured DCN. For assessing applicability of real-time and online DCN sensing, the Raman spectrometer was integrated with a flow cell capable of allowing measurements of DCN in flowing fuel samples and included the optimal ANN model of the fingerprint region and the 100-feature GS-ANN model on a Raspberry Pi computer. A number of unseen F-24/alcohol-to-jet fuel mixtures composed of unknown volumes were tested using the flow cell for DCN, and all of these samples were predicted within 10 % of the measured DCN.

The overview of analytical methods for studying of fossil natural resins

The review presents methods that are used frequently for multi-analytical study of fossil resins. The preliminary characterization relies on physical methods such as microhardness, density and fluorescence in UV light measurements. The spectroscopic methods: infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy are also presented in the paper. Besides that, the review also contains examples of the application of chromatographic methods: gas chromatography, thin layer chromatography, high-performance liquid chromatography, two-dimensional gas chromatography coupled to time-of-flight mass spectrometry as well as sample preparation methods for chromatographic studies such as pyrolysis. Additionally, thermal methods such as thermogravimetric analysis and differential scanning calorimetry also are covered by the review. Beside the examples of application, a detailed description with development history and perspective for further improvement are presented for each method. Moreover, fit-for-purpose assessment of each method is illustrated based on many examples from literature. The paper also contains examples of the application of multivariate statistical analysis and chemometric methods for comparing multiple properties of different fossil resin specimens for differentiation and classification purposes.

A Review of Pharmaceutical Robot based on Hyperspectral Technology

The quality and safety of medicinal products are related to patients’ lives and health. Therefore, quality inspection takes a key role in the pharmaceutical industry. Most of the previous solutions are based on machine vision, however, their performance is limited by the RGB sensor. The pharmaceutical visual inspection robot combined with hyperspectral imaging technology is becoming a new trend in the high-end medical quality inspection process since the hyperspectral data can provide spectral information with spatial knowledge. Yet, there is no comprehensive review about hyperspectral imaging-based medicinal products inspection. This paper focuses on the pivotal pharmaceutical applications, including counterfeit drugs detection, active component analysis of tables, and quality testing of herbal medicines and other medical materials. We discuss the technology and hardware of Raman spectroscopy and hyperspectral imaging, firstly. Furthermore, we review these technologies in pharmaceutical scenarios. Finally, the development tendency and prospect of hyperspectral imaging technology-based robots in the field of pharmaceutical quality inspection is summarized.

Nanostructure-Based Surface-Enhanced Raman Spectroscopy Techniques for Pesticide and Veterinary Drug Residues Screening

Pesticide and veterinary drug residues in food and environment pose a threat to human health, and a rapid, super-sensitive, accurate and cost-effective analysis technique is therefore highly required to overcome the disadvantages of conventional techniques based on mass spectrometry. Recently, the surface-enhanced Raman spectroscopy (SERS) technique emerges as a potential promising analytical tool for rapid, sensitive and selective detections of environmental pollutants, mostly owing to its possible simplified sample pretreatment, gigantic detectable signal amplification and quick target analyte identification via finger-printing SERS spectra. So theoretically the SERS detection technology has inherent advantages over other competitors especially in complex environmental matrices. The progress in nanostructure SERS substrates and portable Raman appliances will promote this novel detection technology to play an important role in future rapid on-site assay. This paper reviews the advances in nanostructure-based SERS substrates, sensors and relevant portable integrated systems for environmental analysis, highlights the potential applications in the detections of synthetic chemicals such as pesticide and veterinary drug residues, and also discusses the challenges of SERS detection technique for actual environmental monitoring in the future.

Temperature-Induced Chemical Changes in Lubricant Automotive Oils Evaluated Using Raman Spectroscopy

Automotive engine lubricating oils are not only intended to reduce friction between parts, but also act on the cooling of motor components and protection of metals against corrosion. To improve its properties and efficiency, additives are added to the base oil for different goals. However, over time of use, external factors modify its properties, such as the engine operating temperature, the frictional force between parts, the mixture of this oil with fuel before burning and with combustion products, causing loss of their efficiency. This work aimed to evaluate, with Raman spectroscopy technique, the temperature-induced changes related to degradation of mineral, semi-synthetic and synthetic automotive lubricating oils. Samples being subject to periodic heating cycle were kept to average temperature of 133 ℃, considering 8 h per day, for six days, until complete 48 h of heating. By analyzing the Raman spectra, it was possible to identify common peaks between the three types of oils and changes caused by heating cycles. Principal components analysis showed that the synthetic oil degraded in less extent than the semi-synthetic one, and this one degraded less than the mineral oil. Spectral models to predict the heating time based on the spectral variations identified using principal components analysis and the regression done using partial least squares, using the heating time as independent variable and the spectral features as dependent variables, was able to predict the heating time for each of oil types with high correlation and prediction error (r > 0.97 and error <4.0 h) for both principal components analysis and partial least squares regression models. Raman technique was able to identify chemical changes resulting from the heating of lubricant oils and to correlate these changes with the heating time, thus becoming a technique of interest for the preventive maintenance area.

Benzene Derivatives Analysis Using Aluminum Nitride Waveguide Raman Sensors

Raman spectroscopy using aluminum nitride (AlN) optical waveguides was demonstrated for organic compound analysis. The AlN waveguide device was prepared by reactive sputtering deposition and complementary-metal-oxide semiconductor (CMOS) processes. A fundamental waveguide mode was observed over a broad visible spectrum and the waveguide evanescent wave was used to excite the Raman signals of the test analytes. The performance of the waveguide sensor was characterized by measuring the Raman spectra of the benzene derivative mixtures consisting of benzene, anisole, and toluene. The compositions and concentrations were resolved by correlating the obtained Raman spectrum with the characteristic Raman peaks associated with C-C, C-H, and C-O functional groups. With the advantages of real-time detection and enhanced Raman signal intensity, the AlN waveguides provided a sensor platform for nondestructive and online chemical compound monitoring.

Fossil Resins–Constraints from Portable and Laboratory Near-infrared Raman Spectrometers

Comparative studies of fossil resins of various ages, botanical sources, geological environments, and provenience were provided via a handheld portable Near-Infrared (NIR)-Raman spectrometer and benchtop instrument both working with laser line 1064 nm. The recorded Raman spectra of individual fossil resins were found to be sufficiently similar irrespective to the device type applied, i.e., handheld or benchtop. Thus, the portable equipment was found to be a sufficient tool for the preliminary identification of resins based on botanical and geographical origin criteria. The observed height ratio of 1640/1440 cm−1 Raman bands did not correlate well with the ages of fossil resins. Hence, it may be assumed that geological conditions such as volcanic activity and/or hydrothermal heating are plausible factors accelerating the maturation of resins and cross-linking processes.

Polarization influence and its mitigation on laser frequency noise measurement by a short-delayed self-homodyne interference method

This paper investigated how a polarization state influences frequency noise measurement accuracy of the short-delayed self-homodyne interference method. An autopolarization control method was demonstrated to mitigate polarization-induced fading (PIF) in a 120-deg phase difference Mach-Zehnder Interferometer (MZI). This method used a feedback adjustment with simulated annealing algorithm, which had the advantages of a short control period, high accuracy, and easy implementation. Frequency fluctuations' power spectral density and linewidth results measured by the improved MZI were consistent with the results of the Michelson interferometer, which used the Faraday rotator mirrors (FRMs) to overcome PIF. The novel MZI structure is unrestricted to FRMs and can extend the capability of the short-delayed self-homodyne interference technique for many special bands' laser frequency noise measurements such as visible bands.

Point-of-care testing in the early diagnosis of acute pesticide intoxication: The example of paraquat

Acute pesticide intoxication is a common method of suicide globally. This article reviews current diagnostic methods and makes suggestions for future development. In the case of paraquat intoxication, it is characterized by multi-organ failure, causing substantial mortality and morbidity. Early diagnosis may save the life of a paraquat intoxication patient. Conventional paraquat intoxication diagnostic methods, such as symptom review and urine sodium dithionite assay, are time-consuming and impractical in resource-scarce areas where most intoxication cases occur. Several experimental and clinical studies have shown the potential of portable Surface Enhanced Raman Scattering (SERS), paper-based devices, and machine learning for paraquat intoxication diagnosis. Portable SERS and new SERS substrates maintain the sensitivity of SERS while being less costly and more convenient than conventional SERS. Paper-based devices provide the advantages of price and portability. Machine learning algorithms can be implemented as a mobile phone application and facilitate diagnosis in resource-limited areas. Although these methods have not yet met all features of an ideal diagnostic method, the combination and development of these methods offer much promise.

Sensitive SERS nanotags for use with a hand-held 1064 nm Raman spectrometer

This is the first report of the use of a hand-held 1064 nm Raman spectrometer combined with red-shifted surface-enhanced Raman scattering (SERS) nanotags to provide an unprecedented performance in the short-wave infrared (SWIR) region. A library consisting of 17 chalcogenopyrylium nanotags produce extraordinary SERS responses with femtomolar detection limits being obtained using the portable instrument. This is well beyond previous SERS detection limits at this far red-shifted wavelength and opens up new options for SERS sensors in the SWIR region of the electromagnetic spectrum (between 950 and 1700 nm).

A portable SERS method for the determination of uric acid using a paper-based substrate and multivariate curve resolution

This paper presents a portable quantitative method for the on-site determination of uric acid in urine using surface-enhanced Raman spectroscopy (SERS) and gold nanoparticle-coated paper as a substrate. A procedure was developed for the rapid preparation of cost-effective SERS substrates that enabled the adequate control of a homogeneous active area and the use of small quantities of gold nanoparticles per substrate. The standard addition method and multivariate curve resolution-alternating least squares (MCR-ALS) were applied to compensate for the matrix effect and to address overlapping bands between uric acid and interference SERS spectra. The proposed methodology demonstrated better performance than conventional univariate methods (in terms of linearity, accuracy and precision), a wide linear range (0-3.5 mmol L(-1)) and an adequate limit of detection (0.11 mmol L(-1)). For the first time, a portable SERS method coupled with chemometrics was developed for the routine analysis of uric acid at clinically relevant concentrations with minimal sample preparation and easy extension for the on-site determination of other biomarkers in complex sample matrices.

Determining Gender by Raman Spectroscopy of a Bloodstain

The development of novel methods for forensic science is a constantly growing area of modern analytical chemistry. Raman spectroscopy is one of a few analytical techniques capable of nondestructive and nearly instantaneous analysis of a wide variety of forensic evidence, including body fluid stains, at the scene of a crime. In this proof-of-concept study, Raman microspectroscopy was utilized for gender identification based on dry bloodstains. Raman spectra were acquired in mapping mode from multiple spots on a bloodstain to account for intrinsic sample heterogeneity. The obtained Raman spectroscopic data showed highly similar spectroscopic features for female and male blood samples. Nevertheless, support vector machines (SVM) and artificial neuron network (ANN) statistical methods applied to the spectroscopic data allowed for differentiating between male and female bloodstains with high confidence. More specifically, the statistical approach based on a genetic algorithm (GA) coupled with an ANN classification showed approximately 98% gender differentiation accuracy for individual bloodstains. These results demonstrate the great potential of the developed method for forensic applications, although more work is needed for method validation. When this method is fully developed, a portable Raman instrument could be used for the infield identification of traces of body fluids and to obtain phenotypic information about the donor, including gender and race, as well as for the analysis of a variety of other types of forensic evidence.

The interface between forensic science and technology: how technology could cause a paradigm shift in the role of forensic institutes in the criminal justice system

In this paper, the importance of modern technology in forensic investigations is discussed. Recent technological developments are creating new possibilities to perform robust scientific measurements and studies outside the controlled laboratory environment. The benefits of real-time, on-site forensic investigations are manifold and such technology has the potential to strongly increase the speed and efficacy of the criminal justice system. However, such benefits are only realized when quality can be guaranteed at all times and findings can be used as forensic evidence in court. At the Netherlands Forensic Institute, innovation efforts are currently undertaken to develop integrated forensic platform solutions that allow for the forensic investigation of human biological traces, the chemical identification of illicit drugs and the study of large amounts of digital evidence. These platforms enable field investigations, yield robust and validated evidence and allow for forensic intelligence and targeted use of expert capacity at the forensic institutes. This technological revolution in forensic science could ultimately lead to a paradigm shift in which a new role of the forensic expert emerges as developer and custodian of integrated forensic platforms.

Hand-portable liquid chromatographic instrumentation

Over the last four decades, liquid chromatography (LC) has experienced an evolution to smaller columns and particles, new stationary phases and low flow rate instrumentation. However, the development of person-portable LC has not followed, mainly due to difficulties encountered in miniaturizing pumps and detectors, and in reducing solvent consumption. The recent introduction of small, non-splitting pumping systems and UV-absorption detectors for use with capillary columns has finally provided miniaturized instrumentation suitable for high-performance hand-portable LC. Fully integrated microfabricated LC still remains a significant challenge. Ion chromatography (IC) has been successfully miniaturized and applied for field analysis; however, applications are mostly limited to inorganic and small organic ions. This review covers advancements that make possible more rapid expansion of portable forms of LC and IC.

Selection of Portable Spectrometers for Planetary Exploration: A Comparison of 532 nm and 785 nm Raman Spectroscopy of Reduced Carbon in Archean Cherts

Knowledge and understanding of the martian environment has advanced greatly over the past two decades, beginning with NASA's return to the surface of Mars with the Pathfinder mission and its rover Sojourner in 1997 and continuing today with data being returned by the Curiosity rover. Reduced carbon, however, is yet to be detected on the martian surface, despite its abundance in meteorites originating from the planet. If carbon is detected on Mars, it could be a remnant of extinct life, although an abiotic source is much more likely. If the latter is the case, environmental carbonaceous material would still provide a source of carbon that could be utilized by microbial life for biochemical synthesis and could therefore act as a marker for potential habitats, indicating regions that should be investigated further. For this reason, the detection and characterization of reduced or organic carbon is a top priority for both the ESA/Roscosmos ExoMars rover, currently due for launch in 2018, and for NASA's Mars 2020 mission. Here, we present a Raman spectroscopic study of Archean chert Mars analog samples from the Pilbara Craton, Western Australia. Raman spectra were acquired with a flight-representative 532 nm instrument and a 785 nm instrument with similar operating parameters. Reduced carbon was successfully detected with both instruments; however, its Raman bands were detected more readily with 785 nm excitation, and the corresponding spectra exhibited superior signal-to-noise ratios and reduced background levels.

Detection of pigments of halophilic endoliths from gypsum: Raman portable instrument and European Space Agency's prototype analysis

A prototype instrument, under development at the University of Leicester, for the future European Space Agency (ESA) ExoMars mission, was used for the analysis of microbial pigments within a stratified gypsum crust from a hypersaline saltern evaporation pond at Eilat (Israel). Additionally, the same samples were analysed using a miniaturized Raman spectrometer, featuring the same 532 nm excitation. The differences in the position of the specific bands, attributed to carotenoid pigments from different coloured layers, were minor when analysed by the ESA prototype instrument; therefore, making it difficult to distinguish among the different pigments. The portable Delta Nu Advantage instrument allowed for the discrimination of microbial carotenoids from the orange/green and purple layers. The purpose of this study was to complement previous laboratory results with new data and experience with portable or handheld Raman systems, even with a dedicated prototype Raman system for the exploration of Mars. The latter is equipped with an excitation wavelength falling within the carotenoid polyene resonance region. The ESA prototype Raman instrument detected the carotenoid pigments (biomarkers) with ease, although further detailed distinctions among them were not achieved.

Miniaturized Raman instrumentation detects carotenoids in Mars-analogue rocks from the Mojave and Atacama deserts

This study is primarily focused on proving the potential of miniaturized Raman systems to detect any biomolecular and mineral signal in natural geobiological samples that are relevant for future application of the technique within astrobiologically aimed missions on Mars. A series of evaporites of varying composition and origin from two extremely dry deserts were studied, namely Atacama and Mojave. The samples represent both dry evaporitic deposits and recent evaporitic efflorescences from hypersaline brines. The samples comprise halite and different types of sulfates and carbonates. The samples were analysed in two different ways: (i) directly as untreated rocks and (ii) as homogenized powders. Two excitation wavelengths of miniaturized Raman spectrometers were compared: 532 and 785 nm. The potential to detect carotenoids as biomarkers on Mars compared with the potential detection of carbonaceous matter using miniaturized instrumentation is discussed.

Spatially compressed dual-wavelength excitation Raman spectrometer

The design and operation of a novel dual-laser excitation Raman instrument is described. The use of two lasers of differing wavelengths allows for a Raman spectrum covering all fundamental modes of vibration to be collected while minimizing fluorescence and allowing for spatial compression of the spectrum on an imaging detector. The use of diode lasers with integrated distributed Bragg reflector gratings facilitates the use of an integrated thermoelectric cooler to allow collection of shifted excitation spectra for both of the lasers, further enhancing the rejection of fluorescence. An example is given, which uses seven excitation wavelengths for each laser to reconstruct the Raman spectrum of a solvent in the presence of a highly fluorescent dye by using a sequentially shifted excitation Raman reconstruction algorithm.

Raman spectroscopy of microbial pigments

Raman spectroscopy is a rapid nondestructive technique providing spectroscopic and structural information on both organic and inorganic molecular compounds. Extensive applications for the method in the characterization of pigments have been found. Due to the high sensitivity of Raman spectroscopy for the detection of chlorophylls, carotenoids, scytonemin, and a range of other pigments found in the microbial world, it is an excellent technique to monitor the presence of such pigments, both in pure cultures and in environmental samples. Miniaturized portable handheld instruments are available; these instruments can be used to detect pigments in microbiological samples of different types and origins under field conditions.

The role of mobile instrumentation in novel applications of Raman spectroscopy: archaeometry, geosciences, and forensics

The applications of analytical Raman spectroscopy in the characterisation of materials associated with archaeologically excavated artefacts, forensic investigations of drugs of abuse, security and crime scenes, minerals and rocks and future astrobiological space missions are now well established; however, these applications have emphasised the need for new developments in the area of miniaturised instrumentation which extends the concept and breadth of the analytical requirement to facilitate the provision of data from 'in field' studies. In this respect, the apparently unrelated themes of art and archaeology, forensic science, geological science and astrobiology as covered by this review are unified broadly by the ability to record data nondestructively and without resorting to sampling and the subsequent transfer of samples to the analytical laboratory. In studies of works of art there has long been a requirement for on-site analysis, especially for valuable paintings held under strict museum security and for wall paintings which cannot physically be removed from their setting; similarly, the use of portable Raman spectroscopy in archaeological and geological field work as a first-pass screening device which obviates the necessity of multiple and wasteful specimen collection is high on the wish-list of practicing spectroscopists. As a first-pass screening probe for forensic crime scenes, Raman spectroscopy has proved to be of inestimable value for the early detection of dangerous and prohibited materials such as drugs of abuse, explosives and their chemical precursors, and banned contraband biomaterials such as ivories and animal products; in these applications the advantage of the Raman spectroscopic technique for the recognition of spectral signatures from mixtures of inorganic and organic compounds is paramount and not afforded by other less portable instrumental techniques. Finally, in astrobiological work, these requirements also apply but with the additional prerequisite for system operation remotely - often over distances of several hundred million kilometres - as part of instrumental suites on robotic spacecraft and planetary landers; this necessitates robust and reliable instrumentation for the observation of unique and characteristic spectral features from the planetary geological surface and subsurface which are dependent on the assignment of both biological and geological band signatures.

The development of surface-enhanced Raman scattering as a detection modality for portable in vitro diagnostics: progress and challenges

This perspective provides an overview of the diverse surface-enhanced Raman scattering (SERS)-based sensor platforms that have been developed for in vitro diagnostic applications. To provide focus, protein and nucleic acid detection assays based on the principle of extrinsic SERS sensing are emphasized, as well as their potential for translation to fully integrated point-of-care (POC) test platforms. The development of intrinsic SERS sensors, which are predicated on the direct detection of analytes by laser excitation, entails unique opportunities and challenges deserving of their own attention. As the robust sensing of disease pathogens and cancers in both clinical facilities and limited resource settings is the targeted objective of many next-generation biosensors, the majority of the research progress summarized here centers on SERS sensors developed for the rapid, sensitive and selective detection of disease-causing pathogens and biomarkers. In our effort to communicate a realistic assessment of the progress that has been made and the challenges that lie ahead, we avoid an overtly optimistic appraisal of the current status of SERS diagnostics that does not tacitly acknowledge the difficulties inherent in aligning SERS-based technologies alongside ELISA and PCR technologies as a complementary method for bioanalyte detection possessing unique advantages.

Practical considerations for the field application of miniaturized portable Raman instrumentation for the identification of minerals

The nondestructive identification of both inorganic and organic compounds without the need for chemical or mechanical sample preparation is an advantage of the Raman spectroscopic analytical technique when applied in situ using miniaturized equipment for the geosciences. This is critically assessed here for several real life geoscientific scenarios in which several groups of minerals were analyzed with emphasis on evaporites, carbonates, and selected types of dark minerals and weak Raman scatterers. The role of individual analytical instrumental parameters such as focal plane precision, exposure time, and ambient light conditions that can affect the acquisition and interpretation of spectroscopic data from these specimens in field conditions was also evaluated.

The miniaturized Raman system and detection of traces of life in halite from the Atacama Desert: some considerations for the search for life signatures on Mars

Raman spectroscopy is being adopted as a nondestructive instrumentation for the robotic exploration of Mars to search for traces of life in the geological record. Here, miniaturized Raman spectrometers of two different types equipped with 532 and 785 nm lasers for excitation, respectively, were compared for the detection of microbial biomarkers in natural halite from the hyperarid region of the Atacama Desert. Measurements were performed directly on the rock as well as on the homogenized, powdered samples prepared from this material-the effects of this sample preparation and the excitation wavelength employed in the analysis are compared and discussed. From these results, 532 nm excitation was found to be superior for the analysis of powdered specimens due to its high sensitivity toward carotenoids and hence a higher capability for their detection at relatively low concentration in bulk powdered specimens. For the same reason, this wavelength was a better choice for the detection of carotenoids in direct measurements made on the rock samples. The 785 nm excitation wavelength, in contrast, proved to be more sensitive toward the detection of scytonemin.

Design Considerations for a Portable Raman Probe Spectrometer for Field Forensics

Raman spectroscopy has been shown to be a viable method for explosives detection. Currently most forensic Raman systems are either large, powerful instruments for laboratory experiments or handheld instruments for in situ point detection. We have chosen to examine the performance of certain benchtop Raman probe systems with the goal of developing an inexpensive, portable system that could be used to operate in a field forensics laboratory to examine explosives-related residues or samples. To this end, a rugged, low distortion line imaging dispersive Raman spectrograph was configured to work at 830 nm laser excitation and was used to determine whether the composition of thin films of plastic explosives or small (e.g., ≤10 μm) particles of RDX or other explosives or oxidizers can be detected, identified, and quantified in the field. With 300 mW excitation energy, concentrations of RDX and PETN can be detected and reconstructed in the case of thin Semtex smears, but further work is needed to push detection limits of areal dosages to the ~1 μg/cm2 level. We describe the performance of several probe/spectrograph combinations and show preliminary data for particle detection, calibration and detection linearity for mixed compounds, and so forth.

Characterization of woody and herbaceous biomasses lignin composition with 1064 nm dispersive multichannel Raman spectroscopy

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 (13)C-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.