Feasibility of peak volume,side pixel and multiple peak registration in high-resolution continuum source atomic absorption spectrometry

In high-resolution continuum source atomic absorption spectrometry (HR-CS AAS) with a pixel detector, such as a charge-coupled device array for signal registration, the absorbance A not only depends on the absorption coefficient, the length of the absorbing layer and the number of absorbing atoms therein, but also on the spectral interval over which the signal is recorded, i.e., the spectral bandwidth per pixel and the number of pixels evaluated. Although the problem of different (absorption and emission) line widths is known for several decades already to exist in conventional line source AAS, it is usually disregarded. By choosing a certain number of pixels in HR-CS AAS a defined wavelength interval can be selected over which the absorbance is recorded. As the numerical values obtained this way are not directly comparable with the conventional absorbance, it is necessary to define new terms and symbols for this kind of signal evaluation. With a steady-state signal the individual pixel absorbance values can be added or integrated, resulting in the unit-free wavelength-selected absorbance (WSA, symbol A_Σ), or the wavelength-integrated absorbance (WIA, symbol A_λ) having a wavelength unit, such as picometers (pm). Similarly, with transient signals one can add-up or integrate (over wavelength) the individual integrated (in time) absorbance values of the selected pixels to obtain the volume under the absorbance peak. This results in the peak volume selected absorbance (PVSA, symbol A_Σ,int), and the peak volume integrated absorbance (PVIA, symbol A_λ,int), with the units second (s) and second times picometer (s pm), respectively. For comparison purposes, however, the integrated absorbance values, i.e., WIA or PVIA, should be used since they are instrument-independent.     

The association constant of the first chloro-copper(II) complex in water to 100°C

The equilibrium constant, K₁, for the reaction Cu²⁺ Cl^? ? [CuCl]⁺ has been determined in the range 15–100°C from spectrophotometric data. The method of analysis, which is widely used, requires both slope and intercept from a reciprocal plot of absorbance against total metal ion concentration. The calculated values of K₁, particularly at low temperature, are very sensitive to the chosen method of data treatment such that the application of weighting factors to the absorbance data for a given photometric accuracy can halve the values. The large variations in K₁ found in the literature are likely to be caused by underestimation of the instability inherent in the method as much as by the neglect of chemical effects such as the formation of higher complexes. By appropriate weighting of the absorbance data an increase in K₁ is apparent above 30°C and the method may have limited usefulness at high temperatures.     

Robust absorbance computations in the analysis of glucose by near-infrared spectroscopy

Procedures for data acquisition and data processing are evaluated for the optimal computation of absorbance values based on Fourier transform near-infrared transmission spectra. Samples consisting of physiological levels (1–20 mM) of glucose in an aqueous matrix of variable levels of bovine serum albumin and triacetin are studied in the combination spectral region (5000–4000 cm⁻¹). The weak glucose signals in this region define a challenging analysis that is extremely sensitive to the effects of instrumental drift. The impact of different procedures for obtaining absorbance estimates is evaluated in the context of multivariate calibration models based on partial least-squares (PLS) regression. Replicate calibration and prediction data acquired over 6 months are used to study the robustness of PLS models with respect to time. The recommended protocol for the absorbance calculations is based on the collection of a large group of individual background spectra during the instrumental warm-up period. Seven procedures are tested for obtaining optimal backgrounds for use with either the calibration or prediction data sets. When the developed methodology is employed, standard errors of prediction are maintained in the range of 1.0 mM for spectra acquired up to 6 months after the collection of the calibration data. This level of performance compares favorably to daily internal cross-validation errors of 0.5–0.9 mM.     

Optimizing data-acquisition schedules in physicochemical experiments : Part 3. Effects of the Standard Errors of Measurement of Absorbance and Time on the Precisions of the Initial Absorbance and Rate Constant Obtained from Optimized Experiments Involving the First-order Decay of an Absorbing Species

By monitoring the absorbance of a solution in which an absorbing species is undergoing first- or pseudo-first-order decay, one can evaluate both the initial absorbance A⁰ and the rate constant k. The precisions of the resulting values depend on the standard errors of measurement of both absorbance and time, which are most conveniently expressed by the dimensionless parameters σ_A/A⁰ and kσ_t. Equations describing these dependences for both the overall precision indexes for the individual parameters and the global overall precision index are given to aid in maximizing the efficiencies and precisions of practical experiments.     

Preparation of photocatalytic nano-ZnO/TiO2 film and application for determination of chemical oxygen demand

A composite nano-ZnO/TiO₂ film as photocatalyst was fabricated with vacuum vaporized and sol-gel methods. The nano-ZnO/TiO₂ film improved the separate efficiency of the charge and extended the range of spectrum, which showed a higher efficiency of photocatalytic than the pure nano-TiO₂ and nano-ZnO film. The photocatalytic mechanism of nano-ZnO/TiO₂ film was discussed, too. A new method for determination of low chemical oxidation demand (COD) value in ground water based on nano-ZnO/TiO₂ film using the photocatalytic oxidation technology was founded. This method was originated from the direct determination of the Mn(VII) concentration change resulting from photocatalytic oxidation of organic compounds on the nano-ZnO/TiO₂ film, and the COD values were calculated from the absorbance of Mn(VII). Under the optimal operation conditions, the detection limit of 0.1 mg l⁻¹, COD values with the linear range of 0.3-10.0 mg l⁻¹ were achieved. The results were in good agreement with those from the conventional COD methods.     

Deuterium exchange in the systems of H2O+/H2O and H3O+/H2O

The reactions of H₂O⁺, H₃O⁺, D₂O⁺, and D₃O⁺ with neutral H₂O and D₂O were studied by tandem mass spectrometry. The H₂O⁺ and D₂O⁺ ion reactions exhibited multiple channels, including charge transfer, proton transfer (or hydrogen atom abstraction), and isotopic exchange. The H₃O⁺ and D₃O⁺ ion reactions exhibited only isotope exchange. The variation in the abundances of all ions involved in the reactions was measured over a neutral pressure range from 0 to 2 × 10⁻⁵ Torr. A reaction scheme was chosen, which consisted of a sequence of charge transfer, proton transfer, and isotopic exchange reactions. Exact solutions to two groups of simultaneous differential equations were determined; one group started with the reaction of ionized water, and the other group started with the reactions of protonated water. A nonlinear least-squares regression technique was used to determine the rate coefficients of the individual reactions in the schemes from the ion abundance data. Branching ratios and relative rate coefficients were also determined in this manner.A delta chi-squared analysis of the results of the model fitted to the experimental data indicated that the kinetic information about the primary isotopic exchange processes is statistically the most significant. The errors in the derived values of the kinetic information of subsequent channels increased rapidly. Data from previously published selected ion flow tube (SIFT) study were analyzed in the same manner. Rigorous statistical analysis showed that the statistical isotope scrambling model was unable to explain either the SIFT or the tandem mass spectrometry data. This study shows that statistical analysis can be utilized to assess the validity of possible models in explaining experimentally observed kinetic behaviors.     

In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.     

A quantitative study of alkyl radical reactions by kinetic spectroscopy III. Absorption spectrum and rate constants of mutual interaction for the ethyl radical

Intrinsic spectral and kinetic parameters have been measured for the ethyl radical, which was formed in the gas phase by the flash photolysis of azoethane. Absolute values of the extinction coefficient ?(λ) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of the ethyl radical. The absorption spectrum is broad, structureless, and comparatively weak; ?(247) = 4.8 × 10² l/mol·cm at the maximum, and the oscillator strength is (9.1 ± 0.5) × 10^?3. This is in good qualitative agreement with a spectrum obtained independently using the technique of molecular modulation spectrometry. The biomolecular reactions of mutual interaction were the only significant reactions of the ethyl radical in this system; kinetic analysis of the second-order decline of the absorbance during the dark period yielded a value of k/?(λ) for each experiment. The rate constant for mutual interaction was evaluated from the product of corresponding measurements of k/?(λ) and ?(λ) individual values are independent of the wavelength of measurement, and the mean value is k = (1.40 ± 0.27) × 10¹⁰ l/mol·sec. The rate constant for mutual combination was derived with the aid of product analysis as k₂ = (1.24 ± 0.23) × 10¹⁰ l/mol·sec; it stands in close agreement with the set of “high” values obtained by direct measurement using a variety of methods.     

Une nouvelle méthode numérique de détermination parspectrophotométrie de constantes d'ionisation sechevauchant

A new method of calculation has been developed to obtain two pK_a values from spectrophotometric data in cases when the values are so close together that the calculations usually applied for individual pK_a values are not appropriate. This technique, in which all the experimental data are used to solve for absorbance of monoprotonated species, pK_a1 and pK_a7 by a “complex” method of optimization, is more general than the classical least-squares method. An application is described.     

Mid-infrared spectroscopy for detection of Huanglongbing (greening) in citrus leaves

In recent years, Huanglongbing (HLB) also known as citrus greening has greatly affected citrus orchards in Florida. This disease has caused significant economic and production losses costing about $750/acre for HLB management. Early and accurate detection of HLB is a critical management step to control the spread of this disease. This work focuses on the application of mid-infrared spectroscopy for the detection of HLB in citrus leaves. Leaf samples of healthy, nutrient-deficient, and HLB-infected trees were processed in two ways (process-1 and process-2) and analyzed using a rugged, portable mid-infrared spectrometer. Spectral absorbance data from the range of 5.15-10.72 μm (1942-933 cm⁻¹) were preprocessed (baseline correction, negative offset correction, and removal of water absorbance band) and used for data analysis. The first and second derivatives were calculated using the Savitzky-Golay method. The preprocessed raw dataset, first derivatives dataset, and second derivatives dataset were first analyzed by principal component analysis. Then, the selected principal component scores were classified using two classification algorithms, quadratic discriminant analysis (QDA) and k-nearest neighbor (kNN). When the spectral data from leaf samples processed using process-1 were used for data analysis, the kNN-based algorithm yielded higher classification accuracies (especially nutrient-deficient leaf class) than that of the other spectral data (process-2). The performance of the kNN-based algorithm (higher than 95%) was better than the QDA-based algorithm. Moreover, among different types of datasets, preprocessed raw dataset resulted in higher classification accuracies than first and second derivatives datasets. The spectral peak in the region of 9.0-10.5 μm (952-1112 cm⁻¹) was found to be distinctly different between the healthy and HLB-infected leaf samples. This carbohydrate peak could be attributed to the starch accumulation in the HLB-infected citrus leaves. Thus, this study demonstrates the applicability of mid-infrared spectroscopy for HLB detection in citrus.     

Simultaneous spectrophotometric estimation of nitrobenzene,aniline, and phenol in a ternary mixture using genetic algorithm

In spectrophotometry, mixtures of chemical constituents cannot be determined simultaneously due to spectral interferences as well as the close λ_max wavelength, the wavelength at which a substance absorbs the most photons. Since the spectra of individual components in a ternary mixture overlap, determining the concentration of individual components using the wavelength of maximum absorbance, λ_max, can lead to a significant error. In this paper, the concentrations of individual components in ternary synthetic mixtures of nitrophenol, aniline, and phenol were estimated simultaneously using a model based on a genetic algorithm and partial least squares. The spectrophotometric data of ternary mixtures with almost identical spectra of nitrobenzene, aniline, and phenol were calibrated using partial least squares modeling without losing prediction capability, and a genetic algorithm method was used to select the appropriate wavelengths for partial least square calibration. The experimental calibration matrix of 27 samples containing a ternary mixture of nitrobenzene (1.0–20.0 mg L^?1), aniline (1.0–15.0 mg L^?1), and phenol (4.0–18.0 mg L^?1) was designed by measuring the absorbance between 200 and 340 nm at a 1 nm wavelength intervals. The model was verified by using six different mixtures with varying concentrations of nitrobenzene, aniline, and phenol. The root mean square error in the prediction of nitrobenzene, aniline, and phenol was 0.1411, 0.1670, and 0.2861 with the genetic algorithm, and 0.3666, 0.6149, and 0.6279 without the genetic algorithm, respectively. This method can be successfully applied to estimate the components in synthetic mixtures accurately. Since this method is accurate and robust, it can be applied to actual industrial wastewater that contains a mixture of toxic chemicals. This eliminates the complications and costs related to separation and purification prior to the analysis using costly chromatographic methods.     

The structure,magnetic and spectral properties of 4-acetylpyridine N-oxide complexes of copper(II) propionates

The synthesis and characterization of CuX₂L; (X = CH₃CH₂COO^?, ClCH₂CH₂COO^?, CH₃CHClCOO^? or CH₃CCl₂COO^?; and L = 4-acetylpyridine N-oxide) is reported. The characterization of these compounds was based on electronic, infrared and EPR spectra, as well as magnetic measurements over the temperature range. Several correlations between the spectral and magnetic data as well as pK_a values of the respective acids were found and discussed. On the basis of spectral and magnetic data the structures of the compounds are discussed.     

Simultaneous Spectrophotometric Determination of Group B Vitamins Using Parallel Factor Analysis: PARAFAC

In this work, a simple and rapid analytical procedure was applied for simultaneous determination of folic acid (vitamin B₀), thiamin (vitamin B₁), riboflavin (vitamin B₂) and pyridoxal (vitamin B₆) based on the absorbance data in the pH range 2.0‐12.0 at 25 °C using parallel factor analysis (PARAFAC). The effect of the pH as the most important factor on the sensitivity of the determination was studied. The spectral data were recorded in 400‐650 nm intervals and a 2‐12 pH range for all four vitamins. The calibration set was constructed in the concentration ranges of 4‐22, 1‐20, 6‐26, and 4‐20 μg mL^?;1 for B₆,B₂,B₁ and B₀, respectively. The root mean squares errors of prediction for the prediction set, (RMSEP), are 0.65, 0.63, 1.13 and 0.34 for B₀,B₁,B₂ and B₆, respectively. The recovery percent for the validation set are in the range of 90.6 to 107.0%. The effect of the experimental conditions and diverse species were discussed. The optimum values of these factors were searched according to the relative standard deviation of the prediction set of mixtures solutions.     

Kinetics of replacement of bridging ligands in a diruthenium(II,III) cation

Tetrakis-μ-propionatodiruthenium(II,III) cation reacts with oxalate, in acidic aqueous solution (0.10 M LiCF₃SO₃, [H⁺] 0.01 M at 29.4°C) in a two-phase process. An initial rapid change results in a small decrease in absorbance. This is ascribed to replacement of one propionate ligand by oxalate. A subsequent slower reaction, of which the rate is proportional to added oxalate concentration (k_bi 1.3 M⁻¹ s⁻¹), corresponds to a relatively large increase of absorbance at 475 nm, the absorbance maximum of the product. The data indicate formation of a bis(μ-oxalato)bis(μ-propionato)diruthenium(II,III) anion with a formation constant K_f > 2 x 10⁴ M⁻¹ and an extinction coefficient of 1.3 x 10³ M⁻¹ cm⁻¹ at 475 nm. A third, much slower, change results in decomposition of that product. The occurrence of replacement of bridging ligands under mild conditions indicates that tris-μ-carboxylatodiruthenium(II,Ill) species (otherwise unknown) function as kinetic intermediates.     

Ultrafast Photoinduced Charge Separation in Wide‐Band‐Capturing Self‐Assembled Supramolecular Bis(donor styryl)BODIPY–Fullerene Conjugates

A new series of self‐assembled supramolecular donor–acceptor conjugates capable of wide‐band capture, and exhibiting photoinduced charge separation have been designed, synthesized and characterized using various techniques as artificial photosynthetic mimics. The donor host systems comprise of a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) containing a crown ether entity at the meso‐position and two styryl entities on the pyrrole rings. The styryl end groups also carried additional donor (triphenylamine or phenothiazine) entities. The acceptor host system was a fulleropyrrolidine comprised of an ethylammonium cation. Owing to the presence of extended conjugation and multiple chromophore entities, the BODIPY host revealed absorbance and emission well into the near‐IR region covering the 300–850 nm spectral range. The donor–acceptor conjugates formed by crown ether–alkyl ammonium cation binding of the host–guest system was characterized by optical absorbance and emission, computational, and electrochemical techniques. Experimentally determined binding constants were in the range of 1–2×10⁵ M ^?1. An energy‐level diagram to visualize different photochemical events was established using redox, computational, absorbance, and emission data. Spectral evidence for the occurrence of photoinduced charge separation in these conjugates was established from femtosecond transient absorption studies. The measured rates indicated ultrafast charge separation and relatively slow charge recombination revealing their usefulness in light‐energy harvesting and optoelectronic device applications. The bis(donor styryl)BODIPY‐derived conjugates populated their triplet excited states during charge recombination.     

A review on distribution coefficient (Kd) of some selected radionuclides in soil/sediment over the last three decades

This review paper presents the different methods to estimate K_d and subsequent compiles of the K_d data on U, Ra, Th, ¹³⁷Cs and ⁶⁰Co in soil/sediment under various aquatic medium based on the extensive literature survey over the last 3-decades (1990–2019). The estimated K_d values show a very wide range and make more difficult to derive generic value. The finding suggests that K_d values are to be estimated for site-specific conditions while assessing the radionuclide transport modeling and risk analysis around the nuclear facilities. Review includes research papers, reports, reviewed papers, dissertations, published compilations and other technical documents.

     

Analysis of questioned documents: A review

During the last years (2000–2014), many publications concerning the forensic analysis of questioned documents have been published, and new techniques and methodologies are nowadays employed to overcome forensic caseworks. This article reviews a comprehensive collection of the works focused on this issue, including dating studies, the analysis of inks from pens and printers, the analysis of paper, the analysis of other samples related to questioned documents and studies on intersecting lines. These sections highlight the most relevant analytical studies by a wide range of analytical techniques. Separation and spectrometric techniques are critically discussed and compared, emphasizing the advantages and disadvantages of each one. Finally, concluding remarks on the research published are included.     

Analysis of the temperature dependence of the high-frequency EMR spectra of Mn ions in the lithium-ion battery material LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>

This paper deals with the analysis of the temperature dependence of high-frequency EMR (HF-EMR) spectra due to Mn³⁺ and Mn⁴⁺ ions in the lithium manganese spinel LiMn₂O₄. A range of powder samples obtained by the sol-gel method with calcinations in several temperature ranges were prepared for this study. Based on the initial characterization carried out by a number of techniques, the physicochemical and structural properties of the samples were earlier determined. Independently, temperature magnetization and HF-EMR measurements were carried out. The EMR spectra vary strongly between samples, indicating possible structural or chemical changes. Quantitative analysis of the temperature dependence of the HF-EMR spectra due to Mn³⁺ and Mn⁴⁺ ions in LiMn₂O₄ is presented in this paper. The spectral analysis concerns the line shape, linewidth, intensity and g-factors. Fittings using the Lorentzian spectral shape and, to a certain extent, the Gaussian spectral shape have been carried out in order to parameterize the temperature dependence of the HF-EMR spectra. This parameterization of the HF-EMR experimental data enables a deeper characterization of the samples. Subsequently, a better insight into the role of the Mn³⁺ and Mn⁴⁺ ions in accounting for the characteristics most suitable for application of LiMn₂O₄ as a cathode material may be gained.     

Complexation copper(II) or magnesium ions with d-glucuronic acid – potentiometric,spectral and theoretical studies

Results of potentiometric and spectral studies have shown that in d-glucuronic acid (GluA) with Cu²⁺ or Mg²⁺ systems, the complexes ML and ML(OH)_x are formed. Overall stability constants (log β) and equilibrium constants (log K_e) were calculated for all complex forms. The mode of coordination for each form was concluded on the basis of spectral values, Vis, EPR, and chemical shifts in the ¹³C NMR. According to spectral analysis, Cu(GluA) exists in two possible forms, which confirm the occurrence of the coordination dichotomy in the system. The main center of interactions in the hydroxyl complexes Cu(GluA)(OH)_x and MgGluA are oxygens from the carboxyl group. Differences in the coordination mode in the copper(II) and magnesium systems at low pH were observed.     

Untargeted screening of unknown xenobiotics and potential toxins in plasma of poisoned patients using high-resolution mass spectrometry: Generation of xenobiotic fingerprint using background subtraction

A novel analytical workflow was developed and applied for the detection and identification of unknown xenobiotics in biological samples. High-resolution mass spectrometry (HRMS)-based data-independent MS^E acquisition was employed to record full scan MS and fragment spectral datasets of test and control samples. Then, an untargeted data-mining technique, background subtraction, was utilized to find xenobiotics present only in test samples. Structural elucidation of the detected xenobiotics was accomplished by database search, spectral interpretation, and/or comparison with reference standards. Application of the workflow to analysis of unknown xenobiotics in plasma samples collected from four poisoned patients led to generation of xenobiotic profiles, which were regarded as xenobiotic fingerprints of the individual samples. Among 19 xenobiotics detected, 11 xenobiotics existed in a majority of the patients' plasma samples, thus were considered as potential toxins. The follow-up database search led to the tentative identification of azithromycin (X5), α-chaconine (X9) and penfluridol (X12). The identity of X12 was further confirmed with its reference standard. In addition, one xenobiotic component (Y5) was tentatively identified as a penfluridol metabolite. The remaining unidentified xenobiotics listed in the xenobiotic fingerprints can be further characterized or identified in retrospective analyses after their spectral data and/or reference compounds are available. This HRMS-based workflow may have broad applications in the detection and identification of unknown xenobiotics in individual biological samples, such as forensic and toxicological analysis and sport enhancement drug screening.