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Applied Spectroscopy
Journal Prestige (SJR): 0.489

Citation Impact (citeScore): 2
Number of Followers: 20

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ISSN (Print) 0003-7028 - ISSN (Online) 1943-3530
Published by Sage Publications

[1176 journals]

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  Pages: 433 - 438
  Abstract: Applied Spectroscopy, Volume 77, Issue 5, Page 433-438, May 2023.
  
  Citation: Applied Spectroscopy
  PubDate: 2023-05-25T05:40:10Z
  DOI: 10.1177/00037028231180063
  Issue No: Vol. 77, No. 5 (2023)
Optical Tomography of Polymeric Microsphere Layers Using Confocal Raman
Microscopy
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  Authors: Alina Syring, Zunhao Wang, Stefan Wundrack, Rainer Stosch, Tobias Voss
  Abstract: Applied Spectroscopy, Ahead of Print.
  In confocal Raman microscopy, depth profiling is a key application that enables analysis of the structural and chemical composition and size of three-dimensional (3D) transparent objects. However, the precise interpretation of a probed sample's Raman depth profile measurement can be significantly affected by both its size and surrounding objects. This study provides a more comprehensive understanding of the observed optical effects at the interface between polymer spheres and different substrates. Ray- and wave-optical simulations support our results. We derive a correction factor that, depending on the instrumental configuration, allows us to determine the nominal dimensions of the scanned objects more accurately from Raman depth profiles. Our studies support the need for careful consideration when employing depth profiling in confocal Raman microscopy for nondestructive, quantitative tomography of 3D objects.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-25T08:44:32Z
  DOI: 10.1177/00037028231175922
Allan Variance Characterization of Compact Fourier Transform Infrared
Spectrometers
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  Authors: George A. Adib, Yasser M. Sabry, Diaa Khalil
  Abstract: Applied Spectroscopy, Ahead of Print.
  Handheld Fourier transform infrared (FT-IR) spectrometers are very promising candidates for several applications where accurate real-time material detection and quantification are needed. Due to their compact size, their mode of operation which does not allow for long warm-up time, and changing environmental conditions, these spectrometers suffer from short-term noise and long-term instabilities which affect their performance. In this work, the effect of long-term multiplicative instabilities on the signal-to-noise ratio (S/N), measured using the 100% line-method, is studied. An expression for the variance, in this case, is deduced. The Allan variance technique is used to identify and quantify the presence of the different types of noises. The methodology is applied to a commercial NeoSpectra scanner module from Si-Ware Systems, Inc.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-25T08:44:03Z
  DOI: 10.1177/00037028231174248
Evaporative Crystallization of Simvastatin from Different Solutions Using
Mid-Frequency Raman Difference Spectra Explanations
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  Authors: Xinyuan Chen, Xiuzhi Chen, Hongyan Sun, Xiumin Li, Shizhao Ren, Can Jin, Hongjun Jin, Fenghua Chen, Rongrong Xue
  Abstract: Applied Spectroscopy, Ahead of Print.
  Amorphous simvastatin (amorphous SIM) and Form I of SIM were prepared separately from SIM acetone (AC)/ethyl acetate (ETAC)/ethanol (ET) solutions by simply controlling the solvent evaporation rate, and the kinetic formation of amorphous SIM from SIM AC/ETAC/ET solutions was explained using mid-frequency Raman difference spectra analysis. The mid-frequency Raman difference spectra analysis results indicate that the amorphous phase has close connections with solutions and might be the bridge, playing an important role in the intermediate phase, between solutions and their outcome polymorphs.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-23T06:22:48Z
  DOI: 10.1177/00037028231166950
Novel Raman Spectroscopy Method for Solutions in Uniform, High-Strength
Electric Field
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  Authors: Gaurav Anand, Samira Safaripour, Craig Snoeyink
  Abstract: Applied Spectroscopy, Ahead of Print.
  A novel method of measuring the influence of high electric fields on the Raman scattering of fluids is introduced, which can help understand various interactions of a fluid with the high electric field. The microfluidic chip can impose highly controlled, uniform electric fields across the measurement volume with blocked electrodes, eliminating spurious reactions at the electrode surface. The developed methodology and the experimental setup are utilized to examine the effect of the electric field on three of the stretching vibrations of ethanol in water–ethanol mixtures with varying concentrations of ethanol and effective electric fields up to 1.0MV/m. The increase in the electric field is seen to broadly decrease the intensity of Raman scattering due to a decrease in the polarizability of the ethanol molecules. Although this effect is uniform for all water-ethanol mixtures, it reduces in mixtures with high weight-fractions of water because of the already reduced polarizability of an ethanol molecule due to hydrogen bonding. The combined effect of hydrogen bonding and increase in temperature due to the alternating high electric field even results in an increase in the magnitude of peak intensity for relatively low-weight fractions of ethanol.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-22T03:29:06Z
  DOI: 10.1177/00037028231175178
Identification of Glucose-6 Phosphate Dehydrogenase Deficient Patients
Using Attenuated Total Reflection Fourier Transform Infrared Spectroscopy
Using Partial Least Squares Discriminant Analysis in Aqueous Blood Samples
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  Authors: Miguela Martin, Molin Wongwattanakul, Noppmats Khemtonglang, Pakaphan Kiatchoosakun, Philip Heraud, Patcharee Jearanaikoon, Bayden R. Wood
  Abstract: Applied Spectroscopy, Ahead of Print.
  Glucose-6 phosphate dehydrogenase (G6PD) deficiency is an X-linked blood disease that affects 400 million people globally and is especially prevalent in malaria-endemic regions. A significant portion of carriers are asymptomatic and undiagnosed posing complications in the eradication of malaria as it restricts the types of drugs used for malaria treatment. A simple and accurate diagnosis of the deficiency is vital in the eradication of malaria. In this study, we investigate the potential of attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) as a diagnostic technique for G6PD deficiency. Venous blood samples were collected in lithium heparin anticoagulant tubes from G6PD partial and fully deficient volunteers, n = 17, and normal volunteers, n = 59, in Khon Kaen, Thailand. Spectra of aqueous and dry samples were acquired of whole blood, plasma, and red blood cells, and modeled using partial least squares discriminant analysis (PLS-DA). PLS-DA modeling resulted in a sensitivity of 0.800 and specificity of 0.800 correctly classifying fully deficient participants as well as a majority of partially deficient females who are often misdiagnosed as normal by current screening methods. The viability of utilizing aqueous samples has always been hindered by the variability of hydration in the sample, but by employing multicurve curve resolution-alternating least squares to subtract water from each sample we are able to produce high-quality spectra with minimized water contributions. The approach shows proof of principle that ATR FT-IR combined with multivariate data analysis could become a frontline screening tool for G6PD deficiency by improving tailored drug treatments and ultimately saving lives.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-19T07:39:40Z
  DOI: 10.1177/00037028231170851
Shifted Excitation Raman Difference Spectroscopy Combined with Wide Area
Illumination and Sample Rotation for Wood Species Classification
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  Authors: Kay Sowoidnich, Michael Towrie, Pavel Matousek
  Abstract: Applied Spectroscopy, Ahead of Print.
  Raman spectroscopy has found its way into a wide range of applications and is successfully applied for qualitative and quantitative studies. Despite significant technical progress over the last few decades, there are still some challenges that limit its more widespread usage. This paper presents a holistic approach to addressing simultaneously the problems of fluorescence interference, sample heterogeneity, and laser-induced sample heating. Long wavelength shifted excitation Raman difference spectroscopy (SERDS) at 830 nm excitation combined with wide-area illumination and sample rotation is presented as a suitable approach for the investigation of selected wood species. Wood as a natural specimen represents a well-suited model system for our study as it is fluorescent, heterogeneous, and susceptible to laser-induced modifications. Two different subacquisition times (50 and 100 ms) and two sample rotation speeds (12 and 60 r/min) were exemplarily assessed. Results demonstrate that SERDS can effectively separate the Raman spectroscopic fingerprints of the wood species balsa, beech, birch, hickory, and pine from intense fluorescence interference. Sample rotation in conjunction with 1 mm-diameter wide-area illumination was suitable to obtain representative SERDS spectra of the wood species within 4.6 s. Using partial least squares discriminant analysis, a classification accuracy of 99.4% for the five investigated wood species was realized. This study highlights the large potential of SERDS combined with wide-area illumination and sample rotation for the effective analysis of fluorescent, heterogeneous, and thermally sensitive specimens in a wide range of application areas.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-17T06:38:26Z
  DOI: 10.1177/00037028231168405
Effect of Tissue Composition and Microstructure on Rabbit Meat Optical
Properties
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  Authors: Hao Yuan, Congyan Li, Fanglin Li, Cailing Liu, Hongying Wang, Xiaohong Xie
  Abstract: Applied Spectroscopy, Ahead of Print.
  To facilitate the design of an optical detection system for assessing rabbit meat quality, nine rabbits of different ages, weights, and varieties were used to collect optical coefficients, compositions, and microstructures from external oblique muscle (EOM) and internal oblique muscle (IOM) samples to research the relationship between them. The results show that rabbit age had a significant influence (P
  Citation: Applied Spectroscopy
  PubDate: 2023-05-10T04:44:33Z
  DOI: 10.1177/00037028231166004
Effect of Sample Plates and Sample Matrix on the Quantification
Capabilities of Surface-Assisted Flowing Atmospheric-Pressure Afterglow
Mass Spectrometry (SA-FAPA-MS)
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  Authors: Maximilian Heide, Carsten Engelhard
  Abstract: Applied Spectroscopy, Ahead of Print.
  Ambient desorption/ionization mass spectrometry (ADI-MS) has been broadly applied to accomplish direct analysis without sample preparation or separation. However, quantification capabilities and analytical performance are sometimes limited. Here, we report signal enhancement effects and improved quantification capabilities in plasma-based ADI-MS, when a flowing atmospheric-pressure afterglow (FAPA) source is used to probe analytes on tailored thin-layer chromatography (TLC) plates. It was found that quantitative results could be achieved when the TLC plate merely served as a sampling plate without a preceding separation step. Specifically, the dynamic response of caffeine, nicotine, acetaminophen, and progesterone was investigated with FAPA-MS on a variety of different TLC surfaces (normal-phase silica, reversed-phase-modified silica, cyano [CN]-modified silica, and dimethyl [RP2]-modified silica). All analytes were studied as single-analyte standards and in a multianalyte mixture to evaluate the effect of sample plates and sample matrix on analytical performance and competitive ionization processes. Overall, dimethyl (RP2)- and CN-modified silica resulted in superior performance compared to other TLC materials. After careful optimization and without the use of internal standards, linear ranges of five orders of magnitude were accessible for caffeine and nicotine. Limits of detection down to femtomole amounts of analyte were achieved. Quantitation limits using RP2-TLC and FAPA-MS were 0.062, 0.062l, 0.31, and 14 pmol for caffeine, nicotine, progesterone, and acetaminophen, respectively. Interestingly, the presence of nicotine at relatively high amounts reduced the signal of the other analytes, an observation that was found to correlate with the differences in the enthalpy of vaporization (ΔHvap) and proton affinity. To prove the quantitative capabilities, nicotine quantification in a real matrix-heavy e-liquid sample was demonstrated using an isotopically labeled standard. The use of TLC-based surfaces with FAPA-MS can aid in the direct and quantitative mass spectrometric investigation of complex mixtures.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-08T06:24:58Z
  DOI: 10.1177/00037028231168617
Selectivity Quantification with the Fluorescent Quantitative
Model-Assisted Semi-Selective Probe (Carbon Dots): Accurate Determination
of Chlortetracycline in Aqueous Environments with Interference
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  Authors: Yang Chen, Xiu-Fang Yan, Jun Bin, Yan-Mei Liang, Fu-Xin Wang, Min Yang, Chao Kang
  Abstract: Applied Spectroscopy, Ahead of Print.
  Probes such as carbon dots (C-dots) have extensive and important applications in the quantitative analysis of complex biological and environmental systems. However, the development of probes is often hindered by incomplete selectivity, i.e., a probe that responds to one substance is also prone to respond to coexisting structurally similar substances. Therefore, the above dilemma often leads to be developed as semi-selective probes, so that the development of probes is abandoned halfway. This work shows how a semi-selective probe can enhance selectivity by combining a proper multivariate calibration model. Primarily, we developed a semi-selective fluorescent probe that responded to tetracyclines (TCs) with discarded tobacco leaves. Then, we introduced the multivariate quantitative fluorescence model (QFM) to enhance its selectivity and solve the problem of fluorescence spectral shift. For the determination of chlortetracycline (CTC) with this semi-selective C-dots probe in mineral and lake water samples and compared to the traditional quantitative model, the introduced QFM resulted in an average relative predictive error (ARPE) in mineral water spiked samples decreased from 57.1 to 5.6%, which reduced the ARPE in the lake water spiked samples from 18.1 to 4.7%. The above results show that the QFM-assisted semi-selective probe C-dots strategy (QFMC−dots) can enhance selectivity, and QFMC−dots achieved high-selective and accurate determination of CTC in interfering mineral and lake water samples, with the limit of detection and limit of quantitation of 0.55 and 1.66 μM, respectively. The proposed strategy of enhancing selectivity by introducing a proper multivariate calibration model can reduce the difficulty and increase success rate of developing probes, which can be expected to provide an interesting alternative for the development of probes, especially when encountering semi-selective problems.
  Citation: Applied Spectroscopy
  PubDate: 2023-05-08T06:22:18Z
  DOI: 10.1177/00037028231167177
Attenuated Total Reflection Fourier Transform Infrared Mapping for the
Identification of the Prescribed and Abnormal Ingredients of Herbal Powder
Preparations
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  Authors: Linying Zhong, Mingshan Xu, Suqin Sun, Qun Zhou, Ling Dong, Jianbo Chen
  Abstract: Applied Spectroscopy, Ahead of Print.
  Herbal powder preparations (HPPs) are common forms of traditional medicine made by blending the powder of two or more ingredients. The first step to ensure the safety and efficacy of HPPs is to confirm the prescribed ingredients and screen the abnormal ingredients. With the help of attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) imaging or mapping, the particles of different ingredients in an HPP sample can be measured individually. In this way, the overlapped absorption signals of different ingredients in the ATR FT-IR spectrum of the bulk sample can be isolated in the ATR FT-IR spectra of the microscopic particles, which leads to the substantial increase of the specificity and sensitivity of the infrared spectral identification method. The characteristic particles of each ingredient can be identified by the objective comparison of the microscopic ATR FT-IR spectra against the reference spectra based on the correlation coefficients. Since the ATR FT-IR imaging or mapping tests of HPPs are free of the separation preprocess, multiple organic and inorganic ingredients are able to be recognized by a single identification procedure simultaneously rather than by different separation and identification procedures. As an example, the ATR FT-IR mapping method was used in this research to successfully identify three prescribed ingredients and two abnormal ingredients in oral ulcer pulvis, which is a classic HPP for oral ulcer in traditional Chinese medicine. The results show the feasibility of the ATR FT-IR microspectroscopic identification method for the objective and simultaneous identification of the prescribed and abnormal ingredients of HPPs.
  Citation: Applied Spectroscopy
  PubDate: 2023-04-27T05:33:37Z
  DOI: 10.1177/00037028231170597
Adversarial Data Augmentation and Transfer Net for Scrap Metal
Identification Using Laser-Induced Breakdown Spectroscopy Measurement of
Standard Reference Materials
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  Authors: Ekta Srivastava, Hyebin Kim, Jaepil Lee, Sungho Shin, Sungho Jeong, Euiseok Hwang
  Abstract: Applied Spectroscopy, Ahead of Print.
  In this study, we propose a transfer learning-based classification model for identifying scrap metal using an augmented training dataset consisting of laser-induced breakdown spectroscopy (LIBS) measurement of standard reference material (SRMs) samples, considering varying experimental setups and environmental conditions. LIBS provides unique spectra for identifying unknown samples without complicated sample preparation. Thus, LIBS systems combined with machine learning methods have been actively studied for industrial applications such as scrap metal recycling. However, in machine learning models, a training set of the used samples may not cover the diversity of the scrap metal encountered in field measurements. Moreover, differences in experimental configuration, where laboratory standards and real samples are analyzed in situ, may lead to a wider gap in the distribution of training and test sets, dramatically reducing the performance of the LIBS-based fast classification system for real samples. To address these challenges, we propose a two-step Aug2Tran model. First, we augment the SRM dataset by synthesizing spectra of unobserved types through attenuation of dominant peaks corresponding to sample composition and generating spectra depending on the target sample using a generative adversarial network. Second, we used the augmented SRM dataset to build a robust real-time classification model with a convolutional neural network, which is further customized for the target scrap metal with limited measurements through transfer learning. For evaluation, SRMs of five representative metal types, including aluminum, copper, iron, stainless steel, and brass, are measured with a typical setup to form the SRM dataset. For testing, scrap metal from actual industrial fields is experimented with three different configurations, resulting in eight different test datasets. The experimental results show that the proposed scheme produces an average classification accuracy of 98.25% for the three experimental conditions, as high as the results of the conventional scheme with three separately trained and executed models. Additionally, the proposed model improves the classification accuracy of arbitrarily shaped static or moving samples with various surface contaminations and compositions, and even for differing ranges of charted intensities and wavelengths. Therefore, the proposed Aug2Tran model can be used as a systematic model for scrap metal classification with generalizability and ease of implementation.
  Citation: Applied Spectroscopy
  PubDate: 2023-04-25T04:41:29Z
  DOI: 10.1177/00037028231170234
Reconstruction of Raman Spectra of Biochemical Mixtures Using Group and
Basis Restricted Non-Negative Matrix Factorization
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  Authors: Kirsty Milligan, Kendra Scarrott, Jeffrey L. Andrews, Alexandre G. Brolo, Julian J. Lum, Andrew Jirasek
  Abstract: Applied Spectroscopy, Ahead of Print.
  Raman spectroscopy is a useful tool for obtaining biochemical information from biological samples. However, interpretation of Raman spectroscopy data in order to draw meaningful conclusions related to the biochemical make up of cells and tissues is often difficult and could be misleading if care is not taken in the deconstruction of the spectral data. Our group has previously demonstrated the implementation of a group- and basis-restricted non-negative matrix factorization (GBR-NMF) framework as an alternative to more widely used dimensionality reduction techniques such as principal component analysis (PCA) for the deconstruction of Raman spectroscopy data as related to radiation response monitoring in both cellular and tissue data. While this method provides better biological interpretability of the Raman spectroscopy data, there are some important factors which must be considered in order to provide the most robust GBR-NMF model. We here evaluate and compare the accuracy of a GBR-NMF model in the reconstruction of three mixture solutions of known concentrations. The factors assessed include the effect of solid versus solutions bases spectra, the number of unconstrained components used in the model, the tolerance of different signal to noise thresholds, and how different groups of biochemicals compare to each other. The robustness of the model was assessed by how well the relative concentration of each individual biochemical in the solution mixture is reflected in the GBR-NMF scores obtained. We also evaluated how well the model can reconstruct original data, both with and without the inclusion of an unconstrained component. Overall, we found that solid bases spectra were generally comparable to solution bases spectra in the GBR-NMF model for all groups of biochemicals. The model was found to be relatively tolerant of high levels of noise in the mixture solutions using solid bases spectra. Additionally, the inclusion of an unconstrained component did not have a significant effect on the deconstruction, on the condition that all biochemicals in the mixture were included as bases chemicals in the model. We also report that some groups of biochemicals achieve a more accurate deconstruction using GBR-NMF than others, likely due to similarity in the individual bases spectra.
  Citation: Applied Spectroscopy
  PubDate: 2023-04-25T04:40:49Z
  DOI: 10.1177/00037028231169971
An Interactive Spectral Analysis Tool for Chemical Identification and
Quantification of Gas-Phase Species in Complex Spectra
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  Authors: Christopher J. Thompson, Neal B. Gallagher, Kendall D. Hughey, Megan K. Dunlap, Tanya L. Myers, Timothy J. Johnson
  Abstract: Applied Spectroscopy, Ahead of Print.
  A spectral analysis tool has been developed to interactively identify and quantify individual gas-phase species from complex infrared absorbance spectra obtained from laboratory or field data. The SpecQuant program has an intuitive graphical interface that accommodates both reference and experimental data with varying resolution and instrumental lineshape, as well as algorithms to readily align the wavenumber axis of a sample spectrum with the raster of a reference spectrum. Using a classical least squares model in conjunction with reference spectra such as those from the Pacific Northwest National Laboratory (PNNL) gas-phase infrared database or simulated spectra derived from the HITRAN line-by-line database, the mixing ratio of each identified species is determined along with its associated estimation error. After correcting the wavelength and intensity of the field data, SpecQuant displays the calculated mixing ratio versus the experimental data for each analyte along with the residual spectrum with any or all analyte fits subtracted for visual inspection of the fit and residuals. The software performance for multianalyte quantification was demonstrated using moderate resolution (0.5 cm–1) infrared spectra that were collected during the time-resolved infrared photolysis of methyl iodide.
  Citation: Applied Spectroscopy
  PubDate: 2023-04-25T04:40:29Z
  DOI: 10.1177/00037028231169304
10 kHz Shifted-Excitation Raman Difference Spectroscopy with
Charge-Shifting Charge-Coupled Device Read-Out for Effective Mitigation of
Dynamic Interfering Backgrounds
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  Authors: Sara Mosca, Kay Sowoidnich, Megha Mehta, William H. Skinner, Benjamin Gardner, Francesca Palombo, Nicholas Stone, Pavel Matousek
  Abstract: Applied Spectroscopy, Ahead of Print.
  In this work we demonstrate an advanced concept of a charge-shifting charge-coupled device (CCD) read-out combined with shifted excitation Raman difference spectroscopy (SERDS) capable of operating at up to 10 kHz acquisition rates for the effective mitigation of fast-evolving interfering backgrounds in Raman spectroscopy. This rate is 10-fold faster than that achievable with an instrument we described previously and is overall 1000-fold faster than possible with conventional spectroscopic CCDs capable of operating at up to ∼10 Hz rates. The speed enhancement was realized by incorporating a periodic mask at the internal slit of an imaging spectrometer permitting a smaller shift of the charge on the CCD (8 pixels) to be required during the cyclic shifting process compared with the earlier design which employed an 80-pixel shift. The higher acquisition speed enables the more accurate sampling of the two SERDS spectral channels, enabling it to effectively tackle highly challenging situations with rapidly evolving interfering fluorescence backgrounds. The performance of the instrument is evaluated for heterogeneous fluorescent samples which are moved rapidly in front of the detection system aiming at the differentiation of chemical species and their quantification. The performance of the system is compared with that of the earlier 1 kHz design and a conventional CCD operated at its maximum rate of 5.4 Hz as previously. In all situations tested, the newly developed 10 kHz system outperformed the earlier variants. The 10 kHz instrument can benefit a number of prospective applications including: disease diagnosis where high sensitivity mapping of complex biological matrices in the presence of natural fluorescence bleaching restricts achievable limits of detection; accurate data acquisition from moving heterogeneous samples (or moving a handheld instrument in front of the sample during data acquisition) or data acquisition under varying ambient light conditions (e.g., due to casting shadows, sample or instrument movement). Other beneficial scenarios include monitoring rapidly evolving Raman signals in the presence of largely static background signals such as in situations where a heterogeneous sample is moving rapidly in front of a detection system (e.g., a conveyor belt) in the presence of static ambient light.
  Citation: Applied Spectroscopy
  PubDate: 2023-04-25T04:40:08Z
  DOI: 10.1177/00037028231167441
Development of the Pseudomonas syringae pv. morsprunorum Biofilm Monitored
in Real Time Using Attenuated Total Reflection Fourier Transform Infrared
Measurements in a Flow Cell Chamber
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  Authors: Jakub Budil, Pavla Štenclová, Alexander Kromka, Petra Lišková
  Abstract: Applied Spectroscopy, Ahead of Print.
  Biofilms of sessile Pseudomonas syringae cells formed on top of plant host's leaves or fruits allow surviving harsh environmental conditions (desiccation) and improve their resistance to antibacterial treatments of crops. A better understanding of these biofilms can help minimize their effect on harvests. In the present study, infrared attenuated total reflection spectroscopy coupled with optical and confocal laser scanning microscopy has been applied for the first time to analyze Pseudomonas syringae pathovar morsprunorum biofilm development in real time. The biofilm development was observed within a spectral window 4000–800 cm−1 under constant flow conditions for 72 h. The kinetics of representative integrated band areas (nucleic acids with polysaccharides at 1141–1006 cm−1, amino acid side chains with free fatty acids at 1420–1380 cm−1, proteins at 1580–1490 cm−1, and lipids with proteins at 2935–2915 cm−1) were analyzed with regard to the observed biofilm structure and the following P. syringae biofilm developmental stages were attributed: The inoculation phase, washing of weakly attached bacteria closely followed by recolonization of the vacated surface, the restructuration phase, and finally the maturation phase.
  Citation: Applied Spectroscopy
  PubDate: 2023-04-25T04:39:31Z
  DOI: 10.1177/00037028231165057
Dual-Band Infrared Scheimpflug Lidar Reveals Insect Activity in a Tropical
Cloud Forest
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  Authors: Victor Santos, Cesar Costa-Vera, Pamela Rivera-Parra, Santiago Burneo, Juan Molina, Diana Encalada, Jacobo Salvador, Mikkel Brydegaard
  Abstract: Applied Spectroscopy, Ahead of Print.
  We describe an entomological dual-band 808 and 980 nm lidar system which has been implemented in a tropical cloud forest (Ecuador). The system was successfully tested at a sample rate of 5 kHz in a cloud forest during challenging foggy conditions (extinction coefficients up to 20 km–1). At times, the backscattered signal could be retrieved from a distance of 2.929 km. We present insect and bat observations up to 200 m during a single night with an emphasis on fog aspects, potentials, and benefits of such dual-band systems. We demonstrate that the modulation contrast between insects and fog is high in the frequency domain compared to intensity in the time domain, thus allowing for better identification and quantification in misty forests. Oscillatory lidar extinction effects are shown in this work for the first time, caused by the combination of dense fog and large moths partially obstructing the beam. We demonstrate here an interesting case of a moth where left- and right-wing movements induced oscillations in both intensity and pixel spread. In addition, we were able to identify the dorsal and ventral sides of the wings by estimating the corresponding melanization with the dual-band lidar. We demonstrate that the wing beat trajectories in the dual-band parameter space are complementary rather than covarying or redundant, thus a dual-band entomological lidar approach to biodiversity studies is feasible in situ and endows species specificity differentiation. Future improvements are discussed. The introduction of these methodologies opens the door to a wealth of possible experiments to monitor, understand, and safeguard the biological resources of one of the most biodiverse countries on Earth.
  Citation: Applied Spectroscopy
  PubDate: 2023-04-19T04:48:56Z
  DOI: 10.1177/00037028231169302
Development of Raman Calibration Model Without Culture Data for In-Line
Analysis of Metabolites in Cell Culture Media
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  Authors: Risa Hara, Wataru Kobayashi, Hiroaki Yamanaka, Kodai Murayama, Soichiro Shimoda, Yukihiro Ozaki
  Abstract: Applied Spectroscopy, Ahead of Print.
  In this study, we developed a method to build Raman calibration models without culture data for cell culture monitoring. First, Raman spectra were collected and then analyzed for the signals of all the mentioned analytes: glucose, lactate, glutamine, glutamate, ammonia, antibody, viable cells, media, and feed agent. Using these spectral data, the specific peak positions and intensities for each factor were detected. Next, according to the design of the experiment method, samples were prepared by mixing the above-mentioned factors. Raman spectra of these samples were collected and were used to build calibration models. Several combinations of spectral pretreatments and wavenumber regions were compared to optimize the calibration model for cell culture monitoring without culture data. The accuracy of the developed calibration model was evaluated by performing actual cell culture and fitting the in-line measured spectra to the developed calibration model. As a result, the calibration model achieved sufficiently good accuracy for the three components, glucose, lactate, and antibody (root mean square errors of prediction, or RMSEP = 0.23, 0.29, and 0.20 g/L, respectively). This study has presented innovative results in developing a culture monitoring method without using culture data, while using a basic conventional method of investigating the Raman spectra of each component in the culture media and then utilizing a design of experiment approach.
  Citation: Applied Spectroscopy
  PubDate: 2023-03-18T08:11:56Z
  DOI: 10.1177/00037028231160197
Portable Diffuse Reflectance Spectroscopy of Potato Leaves for
Pre-Symptomatic Detection of Late Blight Disease
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  Authors: Chen Zhou, Victor G. Bucklew, Perry S. Edwards, Chenji Zhang, Jinkai Yang, Philip J. Ryan, David P. Hughes, Xinshun Qu, Zhiwen Liu
  Abstract: Applied Spectroscopy, Ahead of Print.
  We report on the use of leaf diffuse reflectance spectroscopy for plant disease detection. A smartphone-operated, compact diffused reflectance spectrophotometer is used for field collection of leaf diffuse reflectance spectra to enable pre-symptomatic detection of the progression of potato late blight disease post inoculation with oomycete pathogen Phytophthora infestans. Neural-network-based analysis predicts infection with>96% accuracy, only 24 h after inoculation with the pathogen, and nine days before visual late blight symptoms appear. Our study demonstrates the potential of using portable optical spectroscopy in tandem with machine learning analysis for early diagnosis of plant diseases.
  Citation: Applied Spectroscopy
  PubDate: 2023-03-17T10:24:46Z
  DOI: 10.1177/00037028231165342
Fourier Transform Infrared Reflection Anisotropy Spectroscopy of
Semiconductor Crystals and Structures: Development and Application in the
Mid-Infrared
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  Authors: Dmitrii D. Firsov, Semyon A. Khakhulin, Oleg S. Komkov
  Abstract: Applied Spectroscopy, Ahead of Print.
  A new method of reflection anisotropy spectroscopy (RAS) with increased mid-IR efficiency owing to the use of a Fourier transform infrared (FT-IR) spectrometer has been developed. An optical setup was implemented using a photoelastic modulator (PEM) to modulate the direction of linear polarization of the probe beam originating from the Michelson interferometer. An original measurement algorithm was proposed to eliminate the influence of spectral inhomogeneity of the PEM efficiency on the obtained spectra using appropriate calibration. It was shown that to preserve the sign of the RAS signal, it is necessary to use a specialized procedure for phase correction of the interferogram registered by the FT-IR spectrometer. In the visible range, good agreement was confirmed between the obtained reflection anisotropy (RA) spectra of a semiconductor crystal and the results of independent measurements using a conventional diffraction-grating spectrometer–based setup. The RA spectrum of a III–V semiconductor heterostructure in the mid-infrared range (λ up to 8 µm) is demonstrated. Application of the developed FT-IR RAS method to layered black phosphorus has enabled characterization of anisotropic interband transitions in this graphene-like semiconductor crystal.
  Citation: Applied Spectroscopy
  PubDate: 2023-03-06T01:04:27Z
  DOI: 10.1177/00037028231153421
Quantitative Raman Cross-Sections and Band Assignments for Fentanyl and
Fentanyl Analogs
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  Authors: Phillip G. Wilcox, Erik D. Emmons, Ian J. Pardoe, Neal D. Kline, Jason A. Guicheteau
  Abstract: Applied Spectroscopy, Ahead of Print.
  Raman cross sections and spectra were measured for five synthetic opioid fentanyl analogs: fentanyl citrate, sufentanil citrate, alfentanil HCl, carfentanil oxalate, and remifentanil HCl. The measurements were performed with excitation wavelengths in the visible (532 nm) and near infrared (785 nm). In addition, density functional theory (DFT) calculations were employed to generate simulated spectra of the compounds and aid in identification of the observed spectral modes. These cross-section measurements and calculations were also used to assess results from a series of measurements of fentanyls cut with other powdered materials. These measurements are valuable for assessment of field-deployable Raman chemical sensors for detection of fentanyl and fentanyl analogs, including when mixed with other materials.
  Citation: Applied Spectroscopy
  PubDate: 2023-03-04T03:30:17Z
  DOI: 10.1177/00037028231160565
Coherent Anti-Stokes Raman Scattering Measurements of Time and Length
Scales of Temperature Fluctuations in a Turbulent Flame
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  Authors: Vitaly D. Kobtsev, Dimitrii N. Kozlov, Sergey A. Kostritsa, Sergey N. Orlov, Valery V. Smirnov, Sergey Y. Volkov
  Abstract: Applied Spectroscopy, Ahead of Print.
  The ability to derive temporal and spatial scales of “instantaneous” local temperature variations in a turbulent flame by means of coherent anti-Stokes Raman scattering (CARS) spectroscopy is demonstrated, for the first time to our knowledge. The measurements employed two CARS spectrometers with synchronized nanosecond pulse-repetitive lasers. The system was enabling to record, with a high temporal resolution of about 10 ns, series of single laser shot CARS spectra of N2 molecules from two spatially overlapped or displaced probe volumes as small as 0.03 × 0.03 × 2 mm3. The spectra were being recorded at a variable delay between two sequential shots, following each other in pairs at a repetition rate of 10 Hz. The series of 500 coupled measurements, at the delays in the range 1 μs–10 ms and the displacements up to 2.5 mm, have been performed in a few points of an open premixed methane–air flame of a laboratory burner with the time-averaged temperatures in the range 1200–1800 K. From the spectra, “instantaneous” temperatures, at the given delay and probe volume distance, have been derived. This allowed the auto-correlation coefficients of temperature fluctuations versus the delay and the displacement to be calculated. These dependences enabled to evaluate temperature correlation times and lengths under various mixture flow rates and equivalence ratios.
  Citation: Applied Spectroscopy
  PubDate: 2023-02-25T07:42:09Z
  DOI: 10.1177/00037028231160797
Infrared Spectroscopy to Analyze Sexual Dimorphism of Hard Dental Tissue
Maturation at Eruption in Patients with Connective Tissue Dysplasia
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  Authors: Andrey S. Korshunov, Vladimir D. Vagner, Kirill N. Kuryatnikov, Dmitriy O. Serov, Andrey L. Torohov, Dzheyhuna D. Shykhalieva, Elena A. Sarf, Lyudmila V. Bel’skaya
  Abstract: Applied Spectroscopy, Ahead of Print.
  The aim of this study was to research the biochemical changes in the hard tissues of the lower “wisdom” teeth, which are at the stage of eruption, with connective tissue dysplasia, depending on sex. The study involved 38 patients aged 17–25 years, who had the extraction of the lower third molars on the left and right for medical reasons. Twenty-one participants in the experiment (16 females, five males) were diagnosed with connective tissue dysplasia; the remaining 17 were healthy and made up the control group (11 females, six males). Samples of enamel, dentin, and enamel–dentin junction were dried to constant weight and examined in tablets pressed in a mixture with potassium bromide on an FT-801 Fourier transform infrared (FT-IR) spectrometer (NPF Simex, Russia) in the range of 500–4000 cm−1. In the IR spectra of the enamel, enamel–dentin junction, and dentin, the absorbance ratio of amide I and II changed significantly and the absorbance of the absorption band of phosphate ions decreased from enamel to dentin. Differences between groups with and without connective tissue dysplasia increased in the following series: dentin, enamel–dentin junction, and enamel. With connective tissue dysplasia, a change in the ratio of the intensities of the absorption bands of amide I and phosphate ions was observed. Normally, the content of organic substances in the enamel of the teeth in the males group is lower than in the females group. Against the background of connective tissue dysplasia, the content of organic substances in the enamel in women decreased while in men it increased, which confirmed the presence of sexual dimorphism during the maturation of hard dental tissues at the eruption stage. The study confirms the opinion of many researchers about the significant role of collagen proteins, which, together with non-collagen proteins, are involved in the development and maturation of dental hard tissues, which are characterized by pronounced heterogeneity and sexual dimorphism in the group with connective tissue dysplasia.
  Citation: Applied Spectroscopy
  PubDate: 2023-02-24T07:01:01Z
  DOI: 10.1177/00037028231160145
Diffuse Reflectance Spectroscopy and Principal Component Analysis to
Retrospectively Determine Production History of Plutonium Dioxide
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  Authors: Eliel Villa-Aleman, Jonathan H. Christian, Jason R. Darvin, Bryan J. Foley, Don D. Dick, Brent Fallin, Kimberly A. S. Fessler
  Abstract: Applied Spectroscopy, Ahead of Print.
  Diffuse reflectance spectroscopy measurements in the shortwave infrared (930–1600 nm) spectral region were acquired for Pu2(C2O4)3•9H2O and its thermal decomposition product, PuO2. We analyzed a total of eight PuO2 samples that were produced at different calcination temperatures (300, 350, 450, 525, 600, 675, 750, and 900 °C). Our goal was to identify spectroscopic fingerprints that could be used to gain retrospective information regarding the production parameters of these important nuclear compounds. The diffuse reflectance spectrum of Pu2(C2O4)3•9H2O features several broad bands that currently preclude detailed analysis. However, all PuO2 samples produced relatively sharp spectral features that got sharper and more intense for samples that were produced at higher calcination temperatures. The electronic band observed at 1433 nm in the diffuse reflectance spectra of PuO2 was found to be a sensitive indicator of crystallinity; a result that is corroborated by ancillary Raman spectroscopy measurements. Principal component analysis of diffuse reflectance spectra was able to clearly rank and categorize PuO2 samples based on the calcination temperature that was employed during their production. Thus, we show herein that important retrospective information pertaining to the process history of PuO2 can be gained through the relatively simplistic combination of diffuse reflectance spectroscopy and principal component analysis. This discovery presents a new method for determining the provenance and process history of PuO2 and should have an impact in the fields of nuclear forensics and nuclear nonproliferation.
  Citation: Applied Spectroscopy
  PubDate: 2023-02-17T07:06:58Z
  DOI: 10.1177/00037028221145724
Coupling of the Liquid Sampling–Atmospheric Pressure Glow Discharge to
Orbitrap Mass Analyzers for Uranium Isotope Ratio Analysis: Evolution of
the Methodology and Implications to the Field
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  Authors: David W. Koppenaal, R. Kenneth Marcus
  Abstract: Applied Spectroscopy, Ahead of Print.
  Just over a decade ago, a truly outside-of-the-box approach to isotope ratio mass spectrometry (IRMS) was undertaken between research groups at Clemson University and the Pacific Northwest National Laboratory. The original motivation dealt with projections as to whether or not microplasmas could be developed into practical elemental ionization sources, perhaps for transportable analysis applications. In particular, the use of the liquid sampling–atmospheric pressure glow discharge (LS-APGD) was pursued. Its interfacing to an ultra-high resolution Orbitrap platform, proved not only facile, but opened up a wealth of potential applications. Here, we lay out a historical, tutorial description of the interfacing and the evolution of the methodology regarding IRMS of uranium. Practical challenges and opportunities are described, which hopefully provide guidance to further applications in high resolution IRMS. It is hoped that, while detailed and lengthy, the didactic nature of the presentation provides experimental insights and tips, and also serves as an homage to our very good friend, Professor Gary M. Hieftje, whose scientific inspiration and comradery have been immeasurably important in our own careers.
  Citation: Applied Spectroscopy
  PubDate: 2023-01-13T07:47:57Z
  DOI: 10.1177/00037028221147927
Spatiotemporal Plasma-Particle Characterization of Dry Aerosols Using
Nanosecond, Femtosecond, and Filament Laser-Produced Plasmas
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  Authors: Kyle S. Latty, Kyle C. Hartig
  Abstract: Applied Spectroscopy, Ahead of Print.
  The ability to rapidly characterize dry aerosols in air using laser-induced breakdown spectroscopy (LIBS) with femtosecond laser pulses promises advancement towards real-time atmospheric sampling and standoff capabilities. Of particular interest is the ability to apply LIBS in the context of low-particle loaded environments where discrete particle interactions must be observed within the sampling volume of the laser-produced plasma (LPP). In this study, dry nanoparticles in suspension are generated from a standard solution and sampled in air using Q-switched nanosecond (ns-) pulses, short-focus (SF) femtosecond (fs-) pulses, and filaments. Short time-gated plasma images are captured to observe spatially and temporally varying discrete plasma-particle interactions, which is shown to influence early air breakdown behavior and subsequent plasma evolution. Along with images, photo-multiplier tube (PMT) measurements are conducted where strong spatiotemporal dependencies are exhibited by the collected emission signal on particle proximity and plasma expansion behavior. Finally, conditional analysis is performed on LIBS measurements to determine associated sampling probabilities and filter out spectra with poor or absent emission peaks with an adaptive threshold algorithm.
  Citation: Applied Spectroscopy
  PubDate: 2022-12-28T01:53:37Z
  DOI: 10.1177/00037028221149480
Near-the-Line Steel Slag Analysis Using Laser-Induced Breakdown
Spectroscopy: Traditional Univariate Versus Machine Learning Calibration
Methods
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  Authors: Jonas Peterson, Melina Gilbert-Gatty, Krister Ekström, Louise Hagesjö, Arne Bengtson
  Abstract: Applied Spectroscopy, Ahead of Print.
  This work is focused on rapid quantitative analysis of slag in the steel industry for improved process control. The novel approach in this work is a direct comparison of two methods to calibrate and quantify spectral data from the slags. Calibration was first done with the most prevalent method in quantitative optical emission spectroscopy (OES) of solids, the univariate ratio method. The second method is an advanced multivariate analysis (MVA) algorithm termed Elastic Net, allowing to include several lines for each element in the calibration functions. In both methods, the output is mass fraction ratios of the analyte element (or compound) to a matrix element (compound). The actual mass fractions of each compound are calculated by sum normalization assuming the matrix to make up the difference up to 100%. The metric used to evaluate the performance of the methods in terms of accuracy is the parameter σrel calculated as the ratio of the root mean square (RMS) deviation from values obtained by X-ray fluorescence (XRF) divided by the average mass fraction of the compound, expressed in percent. A bit surprising, the main outcome of the comparison is that there is very little difference in the performance of the two methods. One exception is the analysis of MgO, where the elastic net gives significantly better accuracy. Presumably, this is due to the use of multiple lines for Mg to build the calibration function. This is very encouraging, since MgO is a major compound in most slags that needs to be determined accurately. It is suggested to improve accuracy further by means of separate calibrations for a limited number of slag types.
  Citation: Applied Spectroscopy
  PubDate: 2022-12-10T08:58:55Z
  DOI: 10.1177/00037028221144654
Elemental Characterization of Leaded and Lead-Free Inorganic Primer
Gunshot Residue Standards Using Single Particle Inductively Coupled Plasma
Time-of-Flight Mass Spectrometry
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  Authors: Sarah E. Szakas, Korina Menking-Hoggatt, Tatiana Trejos, Alexander Gundlach-Graham
  Abstract: Applied Spectroscopy, Ahead of Print.
  This study describes the use of single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) for the detection and classification of inorganic gunshot residue (IGSR) particles. To establish reliable multi-element criteria to classify IGSR particles, leaded and lead-free IGSR reference materials were analyzed, and the elemental compositions of the individual particles were quantified. The results suggest that expanded element compositions may be used to classify IGSR particles via spICP-TOFMS compared to those used in conventional IGSR analysis using scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS). For spICP-TOFMS analysis of leaded IGSR particles, classification may be based on the presence of lead (Pb), antimony (Sb), and barium (Ba) just as in SEM-EDS; however, additional particle types, such as lead-copper (Pb–Cu) particles, contribute significantly (∼30%) to the leaded IGSR particle population. In lead-free IGSR particles, the dominate multi-metal particle composition found is titanium–zinc (Ti–Zn) with a conserved Zn:Ti ratio of 1.4:1, but other elements, such as copper (Cu), are also characteristic. In mixtures of the two IGSR reference materials, we were able to classify over 80% of the multi-metal particles detected with no false-positive particle-type assignments. With spICP-TOFMS, particles smaller than those typically measured by SEM-EDS are detected, with estimated median diameters for leaded and lead-free IGSR of 180 and 320 nm, respectively. Through measuring these smaller particles, up to ∼two times more particles per mL are recorded by spICP-TOFMS compared to that found by SEM-EDS. Overall, high-sensitivity and high-throughput analysis using spICP-TOFMS enables quantitative, rapid multi-elemental characterization, and classification of individual IGSR particles.
  Citation: Applied Spectroscopy
  PubDate: 2022-11-29T12:59:18Z
  DOI: 10.1177/00037028221142624
Two-Dimensional Clustering of Spectral Changes for the Interpretation of
Raman Hyperspectra
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  Authors: H. Georg Schulze, Shreyas Rangan, Martha Z. Vardaki, Michael W. Blades, Robin F. B. Turner, James M. Piret
  Abstract: Applied Spectroscopy, Ahead of Print.
  Two-dimensional correlation spectroscopy (2D-COS) is a technique that permits the examination of synchronous and asynchronous changes present in hyperspectral data. It produces two-dimensional correlation coefficient maps that represent the mutually correlated changes occurring at all Raman wavenumbers during an implemented perturbation. To focus our analysis on clusters of wavenumbers that tend to change together, we apply a k-means clustering to the wavenumber profiles in the perturbation domain decomposition of the two-dimensional correlation coefficient map. These profiles (or trends) reflect peak intensity changes as a function of the perturbation. We then plot the co-occurrences of cluster members two-dimensionally in a manner analogous to a two-dimensional correlation coefficient map. Because wavenumber profiles are clustered based on their similarity, two-dimensional cluster member spectra reveal which Raman peaks change in a similar manner, rather than how much they are correlated. Furthermore, clustering produces a discrete partitioning of the wavenumbers, thus a two-dimensional cluster member spectrum exhibits a discrete presentation of related Raman peaks as opposed to the more continuous representations in a two-dimensional correlation coefficient map. We demonstrate first the basic principles of the technique with the aid of synthetic data. We then apply it to Raman spectra obtained from a polystyrene perchlorate model system followed by Raman spectra from mammalian cells fixed with different percentages of methanol. Both data sets were designed to produce differential changes in sample components. In both cases, all the peaks pertaining to a given component should then change in a similar manner. We observed that component-based profile clustering did occur for polystyrene and perchlorate in the model system and lipids, nucleic acids, and proteins in the mammalian cell example. This confirmed that the method can translate to “real world” samples. We contrast these results with two-dimensional correlation spectroscopy results. To supplement interpretation, we present the cluster-segmented mean spectrum of the hyperspectral data. Overall, this technique is expected to be a valuable adjunct to two-dimensional correlation spectroscopy to further facilitate hyperspectral data interpretation and analysis.
  Citation: Applied Spectroscopy
  PubDate: 2022-10-14T06:58:53Z
  DOI: 10.1177/00037028221133851
Remote Raman Sensing Using a Single-Grating Monolithic Spatial Heterodyne
Raman Spectrometer: A Potential Tool for Planetary Exploration
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  Authors: Evan M. Kelly, Miles J. Egan, Arelis Colόn, S Michael Angel, Shiv K. Sharma
  Abstract: Applied Spectroscopy, Ahead of Print.
  Advances in Raman instrumentation have led to the implementation of a remote dispersive Raman spectrometer on the Perseverance rover on Mars, which is used for remote sensing. For remote applications, dispersive spectrometers suffer from a few setbacks such as relatively larger sizes, low light throughput, limited spectral ranges, relatively low resolutions for small devices, and high sensitivity to misalignment. A spatial heterodyne Raman spectrometer (SHRS), which is a fixed grating interferometer, helps overcome some of these problems. Most SHRS devices that have been described use two fixed diffraction gratings, but a variance of the SHRS called the one-grating SHRS (1g-SHRS) replaces one of the gratings with a mirror, which makes it more compact. In a recent paper we described monolithic two-gratings SHRS, and in this paper, we investigate a single-grating monolithic SHRS (1g-mSHRS), which combines the 1g-SHRS with a monolithic setup previously tested at the University of South Carolina. This setup integrates the beamsplitter, grating, and mirror into a single monolithic device. This reduces the number of adjustable components, allows for easier alignment, and reduces the footprint of the device (35 × 35 × 25 mm with a weight of 80 g). This instrument provides a high spectral resolution (∼9 cm−1) and large spectral range (7327 cm−1) while decreasing the sensitivity to alignment with a field of view of 5.61 mm at 3m. We discuss the characteristics of the 1g-mSHRS by measuring the time-resolved remote Raman spectra of a few inorganic salts, organics, and minerals at 3 m. The 1g-mSHRS makes a good candidate for planetary exploration because of its large spectral range, greater sensitivity, competitively higher spectral resolution, low alignment sensitivity, and high light throughput in a compact easily aligned system with no moving parts.
  Citation: Applied Spectroscopy
  PubDate: 2022-10-12T06:36:56Z
  DOI: 10.1177/00037028221121304
Corrigendum
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  Abstract: Applied Spectroscopy, Ahead of Print.
  
  Citation: Applied Spectroscopy
  PubDate: 2022-07-20T12:07:52Z
  DOI: 10.1177/00037028221088195
Characterization and Optimization of a Spectral Window for Direct Gaseous
Uranium Hexafluoride Enrichment Assay Using Laser-Induced Breakdown
Spectroscopy
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  Authors: George C. Y. Chan, Leigh R. Martin, Richard E. Russo
  Abstract: Applied Spectroscopy, Ahead of Print.
  Through a systematic scanning of 235U and 238U emission lines between 280 nm and 745 nm, the optimal emission line for direct gaseous uranium hexafluoride (UF6) enrichment assay using laser-induced breakdown spectroscopy (LIBS) was found. Screening for spectral features that are potentially useful for U isotopic analysis was gauged from the magnitude of the 235U–238U isotopic shift and the signal-to-background ratio of the emission line through a parameter termed ΔSBR 235U–238U. The ΔSBR spectrum shows peaks at wavelength positions where there are strong lines with significant 235U–238U shifts. The screening identified 13 spectral-window candidates, which were down selected based on their overall accuracy in predicting the 235U enrichment of three UF6 samples of natural (0.720 atom% 235U) and low-enriched (4.675 atom% and 9.157 atom% 235U) grades. The U(I) 646.498 nm emission line, with a determined 235U–238U isotopic shift of −17.7 pm, was found to be the optimal spectral window for direct UF6 enrichment assay. The root mean square error for enrichment assays on the three natural and low-enriched UF6 samples, with each sample measured in six replicates, was 0.31% in absolute 235U content. Each measurement comprised LIBS signals accumulated from 3000 laser shots. The analytical bias and precision were better than 0.5% and 0.3%, respectively, in absolute [235U/(235U + 238U)] ratios. Specific for the two low-enriched UF6 samples, the relative standard deviations from six replicated measurements were around 2%.
  Citation: Applied Spectroscopy
  PubDate: 2022-07-15T03:34:54Z
  DOI: 10.1177/00037028221112953
Smart Error Sum Based on Hybrid Two-Trace Two-Dimensional (2T2D)
Correlation Analysis
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  Authors: Thomas G. Mayerhöfer, Marie Richard-Lacroix, Susanne Pahlow, Uwe Hübner, Jürgen Popp
  Abstract: Applied Spectroscopy, Ahead of Print.
  Based on hybrid 2D correlation analysis, we recently derived and introduced a “smart error sum,” a sophisticated loss function that can be used for solving nonlinear inverse problems like the determination of optical constants and oscillator parameters from a series of optical spectra in the infrared spectral region. The advantage of the smart error sum compared to the conventional sum of squared errors lies in its ability to marginalize multiplicative systematic errors such as, for example, reflectance values above unity in transflection spectra. This is enabled by a transformation, which allows fits to not exclusively focus on forcing fit spectra to agree with experimental spectra at every wavenumber point by all means, but also to take correlations such as spectral similarities and their changes with certain perturbations into account. In this work, we extend our approach to accommodate the treatment of individual spectra, instead of only series, based on hybrid two-trace two-dimensional (2T2D) correlation analysis. We evaluate and prove the value of our approach by individually analyzing experimental transflection spectra of polymethyl methacrylate (PMMA) layers on gold substrates. The comparison of the results with those obtained by the original smart error sum based on the whole set of spectra as well as those resulting from conventional fitting of series and individual spectra (using the conventional sum of squared errors) confirms the validity and soundness of the 2T2D smart error sum.
  Citation: Applied Spectroscopy
  PubDate: 2022-04-22T11:37:38Z
  DOI: 10.1177/00037028221077310