Quantitative Spectroscopic Analysis Research Articles

Quantitative near-infrared spectroscopic analysis of trimethoprim by artificial neural networks combined with modified genetic algorithm

A novel method for rapid, accurate and nondestructive determination of trimethoprim in complex matrix was presented. Near-infrared spectroscopy coupled with multivariate calibration(partial least-squares and artificial neural networks) was applied in the experiment. The variable selection process based on a modified genetic algorithm with fixed number of selected variables was proceeded, which can reduce the training time and enhance the predictive ability when coupled with artificial neural network model.

A Microscopic and Nanoscale Understanding of the Formation of Gold Geochemical Provinces

AbstractGold geochemical provinces in China were delineated through stream sediment or catchment sediment sampling in this study. Each gold geochemical province delineated by a threshold value of 2.5 ng/g covers an area of thousands of kilometers. It is a dilemma that geochemists traditionally thought that gold could not migrate for a long distance in rivers or streams to form a large‐scale geochemical anomaly due to its chemical inertness and high specific density. The quantitative spectroscopic analysis and observations under a scanning electron microscope (SEM) indicate the presence of submicroscopic gold particles (<5 μm in diameter) in large quantities, and observations under a Transmission Electron Microscopy (TEM) further suggest the presence of nanoscale gold particles (several tens of nanometre in diameter) in ores, rocks, soils and stream sediments. Particularly, submicroscopic and nanoscale gold particles less than 5 μm were only found in samples having a low gold content (<10ng/g). This result shows that geochemical provinces, delineated by a threshold value of 2.5 ng/g, are formed by long‐distance transport of ultrafine gold in streams. The findings may provide direct microscopic evidence for gold migration to form geochemical provinces.

WINDS OF LOW-METALLICITY OB-TYPE STARS:HST-COS SPECTROSCOPY IN IC 1613

We present the first quantitative UV spectroscopic analysis of resolved OB stars in IC1613. Because of its alleged very low metallicity (<~1/10 Zo, from HII regions), studies in this Local Group dwarf galaxy could become a significant step forward from the SMC towards the extremely metal-poor massive stars of the early Universe. We present HST-COS data covering the ~1150-1800{\AA} wavelength range with resolution R~2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed PCygni profiles with the SEI method. The vinf-Z relationship has been revisited. The terminal velocity of IC1613 O-stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC1613 and SMC or LMC analogue stars. We find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the vinf/vesc ratio of the whole OB star sample in any of the studied galaxies. Finally, we present first evidence that the Fe-abundance of IC1613 OB stars is similar to the SMC, in agreement with previous results on red supergiants. With the confirmed ~1/10 solar oxygen abundances of B-supergiants, our results indicate that IC1613's [alpha/Fe] ratio is sub-solar.

Catechins and procyanidins of Ginkgo biloba show potent activities towards the inhibition of β-amyloid peptide aggregation and destabilization of preformed fibrils.

Catechins and procyanidins, together with flavonoid glycosides and terpene trilactones, are three important categories of components in the standard extract of Ginkgo biloba leaves (EGb761). In this research, catechins and proanthocyanidins were found to exist in both the extract of Ginkgo leaves and Ginkgo products. By comparing with reference compounds, six of them were identified as (+)-catechin, (−)-epicatechin, (−)-gallocatechin, (−)-epigallocatechin and procyanidins B1 and B3. The activities of these polyphenols in the inhibition of Aβ42 aggregation and the destabilization of preformed fibrils were evaluated using biochemical assays, which showed that all six of the polyphenols, as well as a fraction of the extract of Ginkgo biloba leaves (EGb) containing catechins and procyanidins, exerted potent inhibitory activities towards Aβ42 aggregation and could also destabilize the performed fibrils. Catechins and procyanidins can therefore be regarded as the potent active constituents of EGb761 in terms of their inhibition of Aβ42 aggregation and destabilization of the fibrils. Although quantitative mass spectroscopic analysis revealed that the catechins and procyanidins are only present in low concentrations in EGb761, these components should be studied in greater detail because of their potent inhibitory effects towards Aβ42 aggregation and their ability to destabilize preformed fibrils, especially during the quality control of Ginkgo leaves and the manufacture of Ginkgo products.

Determination of glucose in plasma by dry film-based near infrared spectroscopy: Correcting the thickness variations of dry films without applying an internal standard

The quantitative determination of analytes in plasma by dry film-based near infrared spectroscopy (NIR) is significantly affected by the thickness variations of dry films. Internal standards are generally used to enhance the reproducibility of quantitative results. However, it is difficult to select an appropriate internal standard with general applicability, and the introduction of an internal standard into plasma samples also complicates experimental procedures. In this work, a quantitative NIR transmission spectroscopy model was proposed to explicitly model the effects of the variations in thickness and light scattering characteristics of dry plasma films on NIR transmission measurements, and an advance dual calibration strategy based on support vector regression (DCSSVR) was derived from the proposed quantitative model to realize accurate determination of analytes (e.g. glucose) in dried plasma samples without the use of internal standards. By using the dry film method coupled with the proposed technique, glucose in plasma could be determined over a concentration range of 0.4–20mmolL−1 with satisfactory accuracy (average relative predictive error less than 7.0%) while avoiding any use of internal standards. It can reasonably be expected that the DCSSVR strategy might be of major benefit for the quantitative NIR spectroscopic analysis of analytes of clinical significance in dried biofluid samples.

Preparation and characterization of PEG-modified PCL nanoparticles for oxygen carrier: a new application of Fourier transform infrared spectroscopy for quantitative analysis of the hemoglobin in nanoparticles

The influence of polyethylene glycol (PEG) molar ratio on the nanoparticles (NPs) properties is described herein. Especially, a facile and nondestructive determination route has been raised to quantify the hemoglobin (Hb) amounts in NPs via an internal standard FTIR method. The subsequent results indicated that, briefly, the PEG molar ratio did negligible influence on the size distribution of NPs, however, it did have great effect on the NPs zeta potential and hydrophilicity as well as the Hb loading amount. These findings highlight that the PEG density on the surface is a key parameter affecting the NPs properties.

Quantitative analysis of extracted phycobilin pigments in cyanobacteria-an assessment of spectrophotometric and spectrofluorometric methods.

Phycobilins are an important group of pigments that through complementary chromatic adaptation optimize the light-harvesting process in phytoplankton cells, exhibiting great potential as cyanobacteria species biomarkers. In their extracted form, concentrations of these water-soluble molecules are not easily determined using the chromatographic methods well suited to solvent-soluble pigments. Insights regarding the quantitative spectroscopic analysis of extracted phycobilins also remain limited. Here, we present an in-depth study of two methods that utilize the spectral properties of phycobilins in aqueous extracts. The technical work was carried out using high-purity standards of phycocyanin, phycoerythrin, and allophycocyanin. Calibration parameters for the spectrofluorometer and spectrophotometer were established. This analysis indicated the possibility of detecting pigments in concentrations ranging from 0.001 to 10 μg cm−3. Fluorescence data revealed a reproducibility of 95 %. The differences in detection limits between the two methods enable the presence of phycobilins to be investigated and their amounts to be monitored from oligotrophic to eutrophic aquatic environments.

Feasibility studies of de-sulfurization and de-ashing of low grade medium to high sulfur coals by low energy ultrasonication

The present paper reports an attempt of using low ultrasonic energy (20kHz) to clean some low rank medium to high sulfur coal samples from northeast India in the presence of H2O2 solutions. The study shows satisfactory removal of all the forms of sulfur and mineral matters (ash) from the coal samples. The physico-chemical characterizations of the raw and ultrasonicated coal samples were carried out by using Fourier Transformation Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Thermogravimetry-Derivative Thermogravimetry (TG-DTG) techniques to evaluate the final product quality. The quantitative FT-IR spectroscopic analysis demonstrated the formation of oxidized sulfur species (SO and SO2) and their subsequent removal from the coal samples during ultrasonication. The XRD profiles supported the partial removal of some minerals from the coal including their de-ashing. The TG-DTG profiles of the beneficiated coal revealed their improved quality for use in thermal plants with better combustion efficiency.

ChemInform Abstract: Photonic Crystal Fibres for Chemical Sensing and Photochemistry

AbstractReview: 201 refs.

Analyses of phosmet residues in apples with surface-enhanced Raman spectroscopy

Residual pesticides such as phosmet in fruits and vegetables are one of the major food safety concerns for consumers around the world. Surface-enhanced Raman spectroscopy (SERS) with gold-coated substrates was exploited to analyze phosmet (0.5–10 μg/g) in apples. Phosmet could be detected from its SESR spectra at as low as 1 μg/mL in standard solution and 1 μg/g in apple extracts. The calculated limit of detection for phosmet in standard solution and in apple extracts were 1.01 μg/mL and 1.44 μg/g, respectively. There were linear relationships between the concentrations of phosmet solutions and the Raman intensities of four major characteristic peaks, with the coefficient of determination (R2) ranging from 0.905 to 0.984, the root mean square error of prediction (RMSEP) ranging from 0.46 to 1.16 μg/mL, and the ratio performance deviation (RPD) from 3.22 to 8.21. Although the linear regression results for phosmet in apple extracts with Raman intensities were not as good as those for the standard solutions (R2 = 0.866–0.945, RMSEP = 0.84–1.38 μg/g, RPD = 2.65–4.33, which still showed great potential of using SERS for quantitative analysis. The presence of non-targeted compounds in apple extracts affected the sensitivity for qualitative analysis and accuracy for quantitative analysis. This study demonstrated that SERS coupled with gold nanosubstrates could be used for analysis of trace contaminants like phosmet in complex food matrices.

Automated Quantitative Spectroscopic Analysis Combining Background Subtraction, Cosmic Ray Removal, and Peak Fitting

An integrated concept for post-acquisition spectrum analysis was developed for in-line (real-time) and off-line applications that preserves absolute spectral quantification; after the initializing parameter setup, only minimal user intervention is required. This spectral evaluation suite is composed of a sequence of tasks specifically addressing cosmic ray removal, background subtraction, and peak analysis and fitting, together with the treatment of two-dimensional charge-coupled device array data. One may use any of the individual steps on their own, or may exclude steps from the chain if so desired. For the background treatment, the canonical rolling-circle filter (RCF) algorithm was adopted, but it was coupled with a Savitzky-Golay filtering step on the locus-array generated from a single RCF pass. This novel only-two-parameter procedure vastly improves on the RCF's deficiency to overestimate the baseline level in spectra with broad peak features. The peak analysis routine developed here is an only-two-parameter (amplitude and position) fitting algorithm that relies on numerical line shape profiles rather than on analytical functions. The overall analysis chain was programmed in National Instrument's LabVIEW; this software allows for easy incorporation of this spectrum analysis suite into any LabVIEW-managed instrument control, data-acquisition environment, or both. The strength of the individual tasks and the integrated program sequence are demonstrated for the analysis of a wide range of (although not necessarily limited to) Raman spectra of varying complexity and exhibiting nonanalytical line profiles. In comparison to other analysis algorithms and functions, our new approach for background subtraction, peak analysis, and fitting returned vastly improved quantitative results, even for "hidden" details in the spectra, in particular, for nonanalytical line profiles. All software is available for download.

Selection and identification of streptomycin-specific single-stranded DNA aptamers and the application in the detection of streptomycin in honey

Single-stranded DNA (ssDNA) aptamers specific to streptomycin were screened and identified from a random oligonucleotides library by affinity magnetic beads-based SELEX. After eight rounds of selection, 16 ssDNA with different sequences were identified. Then the dissociation constants (Kd) of these ssDNA were determined and an aptamer (STR1) with highest affinity for streptomycin was identified. Further study showed that aptamer STR1 exhibits very low affinity for other aminoglycoside antibiotics, indicating high specificity. With this aptamer, detection of streptomycin was achieved by using gold nanoparticles (AuNPs)-based colorimetric method. In the presence of streptomycin, the competitive binding of the target and the aptamer decreases the stability of AuNPs in NaCl solution, triggers the aggregation, and exhibits visible color change of AuNPs solution. Through UV–visible spectroscopic quantitative analysis, streptomycin can be detected in the range of 0.2–1.2μM. The presence of other aminoglycoside antibiotics shows neglectable disturbance. Furthermore, the established method was utilized to detect streptomycin in honey, and the same low detection limit and linear detection range were achieved.

Scatter-based quantitative spectroscopic analysis of milk fat and total protein in the region 400–1100 nm in the presence of fat globule size variability

Accurate prediction models for fat and total protein content in raw milk have been built on visible and short-wave near infrared spectra (400–1100nm) of a designed sample set with systematically varied nutrient composition and homogenization degree. Unlike the conventional approach to the spectroscopic milk analysis, exploiting the components' absorbance, the present method basically relies on the phenomenon of light scatter by fat globules and protein micelles.It has been shown that partial least-squares (PLS) regression on raw spectral data results in higher prediction accuracies of fat and total protein content compared to scatter-corrected spectra. Interpretation given to individual PLS factors confirms a dominating role of scatter in the modeling and aids in general understanding of quantitative multivariate analysis based on complex optical responses resulting from multiple scattering by different particles at significantly varying size distributions. This new approach can be used in the raw milk laboratory or field analysis as well as for in-line monitoring of various milk transfer and production stages.Practical modeling issues, i.e. experimental design of the sample set, model validation and refinement, have been also elaborated in this study. Variable selection by interval PLS (iPLS) regression essentially improved the model performance. Selected intervals can be utilized for technical simplification of suggested method of milk analysis.

Micro-patterning of streptavidin-biotin-ampicillin/heparin on poly(tetrafluoroethylene) (PTFE) surfaces: simultaneous antimicrobial and anticoagulant activity.

Formation of heterogeneous and controllable surface patterns on polymeric materials containing antimicrobial and anticoagulant components represent an attractive way of maintaining synthetic materials "clean" from adverse bio-activities. The primary surface "contaminants" are microbial films as well as blood coagulation, both affecting not only performance of internal or external devices, but often exhibiting detrimental effects on patients. In an effort to simultaneously inhibit formation of microbial films and surface blood coagulation multifunctional assemblies containing streptavidin (STR)-biotin bioconjugates were developed on poly(tetrafluoroethylene) (PTFE) surfaces. Using STR conjugated to a biotin-functionalized PTFE surface, spatially controlled micro-patterning was produced by grafting biotinylated polyethylene glycol (B-PEG) to COOH modified PTFE (MA-PTFE), followed by inkjet micro-printing of biotinylated ampicillin (B-AM) and biotinylated heparin (B-HP) molecules. These surfaces exhibit simultaneous antimicrobial and anticoagulant attributes manifested by "zone of inhibition" and anticoagulant measurements. Quantitative spectroscopic analysis revealed that the required surface density of COOH groups on PTFE is 2.94 × 10-7 g cm-2, and B-PEG and STR densities of 9.2 × 10-8 g cm-2 and 3.5 × 10-8 g cm-2, respectively, are sufficient to achieve simultaneous antimicrobial and anticoagulant responses. These studies also showed that the force required to remove STR-biotin conjugates attached to PTFE surfaces measured by atomic force microscopy is approximately 1090 pN, thus providing desirable surface mechanical stability.

Photonic crystal fibres for chemical sensing and photochemistry

In this review, we introduce photonic crystal fibre as a novel optofluidic microdevice that can be employed as both a versatile chemical sensor and a highly efficient microreactor. We demonstrate that it provides an excellent platform in which light and chemical samples can strongly interact for quantitative spectroscopic analysis or photoactivation purposes. The use of photonic crystal fibre in photochemistry and sensing is discussed and recent results on gas and liquid sensing as well as on photochemical and catalytic reactions are reviewed. These developments demonstrate that the tight light confinement, enhanced light-matter interaction and reduced sample volume offered by photonic crystal fibre make it useful in a wide range of chemical applications.

Quantitative spectroscopic analysis of heterogeneous systems: chemometric methods for the correction of multiplicative light scattering effects

Quantitative spectroscopic analysis of heterogeneous systems: chemometric methods for the correction of multiplicative light scattering effects

Absolute Raman intensity measurements and determination of the vibrational second hyperpolarizability of adamantyl endcapped polyynes

Linear sp‐carbon polyynes are ideal molecules for the direct investigation of the physical properties of one‐dimensional conjugated systems. Traditionally, the main obstacle to the study of these systems has been their instability under normal laboratory conditions. Thanks to improved chemical syntheses, a broadened range of polyynes is now available for study, including the hydrocarbon series endcapped with adamantyl groups, Ad[n]. In this work, the quantitative Raman spectroscopic analysis is reported for each member of this homologous series. The Raman scattering intensities corresponding to the major features of the polyyne segment (i.e., the effective conjugation coordinate or Я lines) are then used to evaluate the nonlinear optical (NLO) behavior via determination of the vibrational contribution to the second hyperpolarizability (γvib). This study shows that γvib values as a function of length are of the same order of magnitude as those arising from the electronic contribution to the molecular second hyperpolarizability, γele, as reported for triisopropylsilyl polyynes, TIPS[n], using the differential optical Kerr effect technique. The nonlinear response for Ad[n] polyynes, supported by the analogous response for TIPS[n] polyynes, confirms that linear sp‐carbon molecules have large second hyperpolarizabilities that show a power‐law increase in γ‐values versus length that is larger than other known π‐conjugated systems, such as polyenes. Furthermore, the NLO response of polyynes versus length approaches the theoretical limit described by Kuzyk more closely than other conjugated organic oligomers. Copyright © 2012 John Wiley &amp; Sons, Ltd.

The ARAUCARIA project: Grid-based quantitative spectroscopic study of massive blue stars in NGC 55

The quantitative study of the physical properties and chemical abundances of large samples of massive blue stars at different metallicities is a powerful tool to understand the nature and evolution of these objects. Their analysis beyond the Milky Way is challenging, nonetheless it is doable and the best way to investigate their behavior in different environments. Fulfilling this task in an objective way requires the implementation of automatic analysis techniques that can perform the analyses systematically, minimizing at the same time any possible bias. As part of the ARAUCARIA project we carry out the first quantitative spectroscopic analysis of a sample of 12 B-type supergiants in the galaxy NGC55 at 1.94 Mpc away. By applying the methodology developed in this work, we derive their stellar parameters, chemical abundances and provide a characterization of the present-day metallicity of their host galaxy. Based on the characteristics of the stellar atmosphere/line formation code FASTWIND, we designed and created a grid of models for the analysis of massive blue supergiant stars. Along with this new grid, we implemented a spectral analysis algorithm. Both tools were specially developed to perform fully consistent quantitative spectroscopic analyses of low spectral resolution of B-type supergiants in a fast and objective way. We present the main characteristics of our FASTWIND model grid and perform a number of tests to investigate the reliability of our methodology. The automatic tool is applied afterward to a sample of 12 B-type supergiant stars in NGC55, deriving the stellar parameters and abundances. The results indicate that our stars are part of a young population evolving towards a red supergiant phase. The derived chemical composition hints to an average metallicity similar to the one of the Large Magellanic Cloud, with no indication of a spatial trend across the galaxy.

Observational effects of magnetism in O stars: surface nitrogen abundances

We investigate the surface nitrogen content of the six magnetic O stars known to date as well as of the early B-type star tau Sco. We compare these abundances to predictions of evolutionary models to isolate the effects of magnetic field on the transport of elements in stellar interiors. We conduct a quantitative spectroscopic analysis of the sample stars with state-of-the-art atmosphere models. We rely on high signal-to-noise ratio, high resolution optical spectra obtained with ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic spectra are computed with the code CMFGEN. Values of N/H together with their uncertainties are determined and compared to predictions of evolutionary models. We find that the magnetic stars can be divided into two groups: one with stars displaying no N enrichment (one object); and one with stars most likely showing extra N enrichment (5 objects). For one star (Theta1 Ori C) no robust conclusion can be drawn due to its young age. The star with no N enrichment is the one with the weakest magnetic field, possibly of dynamo origin. It might be a star having experienced strong magnetic braking under the condition of solid body rotation, but its rotational velocity is still relatively large. The five stars with high N content were probably slow rotators on the zero age main sequence, but they have surface N/H typical of normal O stars, indicating that the presence of a (probably fossil) magnetic field leads to extra enrichment. These stars may have a strong differential rotation inducing shear mixing. Our results should be viewed as a basis on which new theoretical simulations can rely to better understand the effect of magnetism on the evolution of massive stars.

A variable differential consensus method for improving the quantitative near-infrared spectroscopic analysis

Consensus methods have presented promising tools for improving the reliability of quantitative models in near-infrared (NIR) spectroscopic analysis. A strategy for improving the performance of consensus methods in multivariate calibration of NIR spectra is proposed. In the approach, a subset of non-collinear variables is generated using successive projections algorithm (SPA) for each variable in the reduced spectra by uninformative variables elimination (UVE). Then sub-models are built using the variable subsets and the calibration subsets determined by Monte Carlo (MC) re-sampling, and the sub-model that produces minimal error in cross validation is selected as a member model. With repetition of the MC re-sampling, a series of member models are built and a consensus model is achieved by averaging all the member models. Since member models are built with the best variable subset and the randomly selected calibration subset, both the quality and the diversity of the member models are insured for the consensus model. Two NIR spectral datasets of tobacco lamina are used to investigate the proposed method. The superiority of the method in both accuracy and reliability is demonstrated.