Applied Spectroscopy
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Is It or Isn't It: The Importance of Visual Classification in Microplastic Characterization Microplastics are a diverse category of pollutants, comprising a range of constituent polymers modified by varying quantities of additives and sorbed pollutants, and exhibiting a range of morphologies, sizes, and visual properties. This diversity, as well as their microscopic size range, presents numerous barriers to identification and enumeration. These issues are addressed with the application of physical and chemical analytical procedures; however, these present new problems associated with researcher training, facility availability and cost, especially for large-scale monitoring programs. Perhaps more importantly, the classifications and nomenclature used by individual researchers to describe microplastics remains inconsistent. In addition to reducing comparability between studies, this limits the conclusions that may be drawn regarding plastic sources and potential environmental impacts. Additionally, where particle morphology data is presented, it is often separate from information on polymer distribution. In establishing a more rigorous and standardized visual identification procedure, it is possible to improve the targeting of complex analytical techniques and improve the standards by which we monitor and record microplastic contamination. Here we present a simple and effective protocol to enable consistent visual processing of samples with an aim to contribute to a higher degree of standardization within the microplastic scientific community. This protocol will not eliminate the need for non-subjective methods to verify plastic objects, but it will standardize the criteria by which suspected plastic items are identified and reduce the costs associated with further analysis.
Applied Spectroscopy - Tập 74 Số 9 - Trang 1139-1153 - 2020
Portable Spectroscopy 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.
Applied Spectroscopy - Tập 72 Số 12 - Trang 1701-1751 - 2018
Sensitivity-Enhanced Fourier Transform Mid-Infrared Spectroscopy Using a Supercontinuum Laser Source Fourier transform infrared (FT-IR) spectrometers have been the dominant technology in the field of mid-infrared (mid-IR) spectroscopy for decades. Supercontinuum laser sources operating in the mid-IR spectral region now offer the potential to enrich the field of FT-IR spectroscopy due to their distinctive properties, such as high-brightness, broadband spectral coverage and enhanced stability. In our contribution, we introduce this advanced light source as a replacement for conventional thermal emitters. Furthermore, an approach to efficient coupling of pulsed mid-IR supercontinuum sources to FT-IR spectrometers is proposed and considered in detail. The experimental part is devoted to pulse-to-pulse energy fluctuations of the applied supercontinuum laser, performance of the system, as well as the noise and long-term stability. Comparative measurements performed with a conventional FT-IR instrument equipped with a thermal emitter illustrate that similar noise levels can be achieved with the supercontinuum-based system. The analytical performance of the supercontinuum-based FT-IR spectrometer was tested for a concentration series of aqueous formaldehyde solutions in a liquid flow cell (500 µm path length) and compared with the conventional FT-IR (130 µm path length). The results show a four-times-enhanced detection limit due to the extended path length enabled by the high brightness of the laser. In conclusion, FT-IR spectrometers equipped with novel broadband mid-IR supercontinuum lasers could outperform traditional systems providing superior performance, e.g., interaction path lengths formerly unattainable, while maintaining low noise levels known from highly stable thermal emitters.
Applied Spectroscopy - Tập 74 Số 4 - Trang 485-493 - 2020
Diffuse Reflectance FT-IR Characterization of Active Sites under Reaction Conditions: The Production of Oxygenates in the CO/H2 Reaction The reactivity of a Lu2 O3 -promoted Rh/Al2 O3 catalyst in the CO/H2 reaction is reported. Methane, heavier hydrocarbons, methanol, and ethanol are obtained. In situ DRIFTS has been employed to record the infrared spectra under the actual reaction conditions. The structure of the observed COads DRIFTS bands has been resolved into its components. The production of oxygenates (methanol and ethanol) has been correlated with the results of the deconvolution calculation. Specific sites for the production of methanol and ethanol in the CO/H2 reaction over a Rh,Lu2 O3 /Al2 O3 catalyst are proposed.
Applied Spectroscopy - Tập 48 Số 10 - Trang 1208-1212 - 1994
Diffuse Reflectance FT-IR Studies of the Adsorption of CO on Rh/Al2O3CatalystsThe diffuse reflectance/FT-IR spectrum of CO/Rh/Al2 O3 system has been investigated in terms of pretreatment of the catalyst, Rh loading, CO pressure (coverage), and coadsorption of CO with oxygen. The widths of all bands were narrowed by Fourier self-deconvolution (FSD), and six types of CO/Rh adsorbed species, including two which have not been assigned previously, have been identified by their C-O stretching frequencies. Species I, assigned to Rh(I)(CO)2 , is formed with isolated Rh atoms and/or edge Rh atoms of atomic “rafts” and/or atomic crystallites. Species II is assigned to Rh(O)-CO. Species III' is assigned to [Rh(O)|2 CO. Species VI is assigned to [Rh(I)]2 CO. Two new species—IIIa, assigned to [Rh(O)]3 CO, with underlying Rh atom, and VI', assigned to [Rh(I))2 (CO)3 —are postulated.
Applied Spectroscopy - Tập 41 Số 4 - Trang 682-688 - 1987
Conversion of Methanol to Dimethylether over ZSM-5 by DRIFT Spectroscopy A diffuse reflectance infrared study of the dehydration of methanol to dimethylether over ZSM-5 catalyst is presented. Between 125° and 200°C, dimethylether is formed and a possible stable intermediate in the nucleophilic attack on surface methoxide groups by methanol is observed on the acid form of the zeolite. This species occupies two OH sites in close proximity. In contrast to the deactivated zeolite, the acid form of ZSM-5 shows an increase in the concentration of terminal silanol groups as the temperature is increased above 100°C and a concurrent increase in reflectivity in the region of the lattice overtone and combination modes.
Applied Spectroscopy - Tập 45 Số 1 - Trang 68-72 - 1991
Reactions of Palladium Acetate in Alkali Chlorides Studied by Variable-Temperature DRIFTS and Mass Spectrometry
Applied Spectroscopy - Tập 45 Số 10 - Trang 1746-1748 - 1991
Simultaneous Analysis of Gas Phase and Intermediates in the Hydrogenation of Carbon Oxides by DRIFTS In this work the experimental details and some examples of applications of diffuse reflectance infrared technique are described. Special interest has been devoted to a correct determination of the temperature of the sample, to gas-phase analysis, and to quantitative aspects in a DRIFTS controlled environmental cell. Applications to the analysis of the gas phase during catalytic hydrogenation and to the obtainment of kinetic parameters for the catalytic decomposition of adsorbates are included.
Applied Spectroscopy - Tập 47 Số 11 - Trang 1760-1766 - 1993
New Procedure for Quantitative Elemental Analysis by Laser-Induced Plasma Spectroscopy A new procedure, based on the laser-induced plasma spectroscopy (LIPS) technique, is proposed for calibration-free quantitative elemental analysis of materials. The method here presented, based on an algorithm developed and patented by IFAM-CNR, allows the matrix effects to be overcome, yielding precise and accurate quantitative results on elemental composition of materials without use of calibration curves. Some applications of the method are illustrated, for quantitative analysis of the composition of metallic alloys and quantitative determination of the composition of the atmosphere.
Applied Spectroscopy - Tập 53 Số 8 - Trang 960-964 - 1999
A Review of the Theory and Application of Coherent Anti-Stokes Raman Spectroscopy (CARS) Coherent anti-Stokes Raman spectroscopy (CARS) is a relatively new kind of Raman spectroscopy which is based on a nonlinear conversion of two laser beams into a coherent, laser-like Raman beam of high intensity in the anti-Stokes region. The emission is often many orders of magnitude greater than normal Raman scattering and, because of the coherent and anti-Stokes character of radiation, the method is very useful for obtaining Raman spectra of fluorescing samples, gases in discharges, plasmas, combustion, atmospheric chemistry. In this paper we outline the basic theory behind CARS and describe its unusual effects and drawbacks. We review the research to date on various materials, and indicate the possible future direction, utility and applications of CARS such as surface studies, fluctuation phenomena, reaction dynamics, photochemistry, kinetics, relaxation, and energy transfer.
Applied Spectroscopy - Tập 31 Số 4 - Trang 253-271 - 1977
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