Interferences of nitrogen dioxide in the determination of aldehydes and ketones by sampling on 2,4-dinitrophenylhydrazine-coated solid sorbent

Summary The influence of nitrogen oxides on the practicability and accuracy of the determination of aldehydes and ketones in air samples using the DNPH-method was examined. Nitrogen dioxide reacts with 2,4-dinitrophenylhydrazine and the reaction products were identified as 2,4-dinitrophenylazide (main product) and 2,4-dinitrochlorobenzene (by-product). They have a similar chromatographic behaviour in high performance liquid chromatography (HPLC) as formaldehyde-2,4-DNP-hydrazone. The chromatographic separation of the reaction products and formaldehyde-2,4-dinitrophenylhydrazone was performed using different gradient systems. Problems which occur in nitrogen dioxide-containing air samples are discussed.     

Independent component analysis applied to diffusion‐ordered spectroscopy: separating nuclear magnetic resonance spectra of analytes in mixtures

Nuclear magnetic resonance spectrum of a mixture contains the overall peaks of all the analytes. It is impossible to perform structural assignment on the mixture without the knowledge of individual spectra of the components. Spectral separation is thus an important means of teasing out pure components of a mixture before spectral assignment. We propose a strategy called diffusion‐ordered independent component analysis (DIFFICA) to achieve this task. This strategy applies independent component analysis algorithms to diffusion‐ordered spectroscopy (DOSY) to extract spectra of pure components in a mixture. DIFFICA was tested in a simulation and experimentally in two three‐component systems with and without water suppression, in 1D and 2D DOSY data. Pure spectra were achieved in both cases. The selection of diffusion parameters to guarantee pure spectra is guided by the distance correlation between separated spectra. Copyright © 2012 John Wiley & Sons, Ltd.     

An attempt to separate A → B process spectra. SEparation by MInimum overLApping Method SEMILAM

It is of particular importance to characterise spectrally each component in the chemical systems in which the reaction proceeds or when the two forms of the same compound exist in equilibrium (tautomerism, cis-trans isomerism, dissociation, etc.). Moreover, physical or chemical separation of the component that is in a smaller amount is always difficult, as well as recording its spectrum. A new simple numerical method of extraction of overlapped spectra of two components is presented. It was termed SEMILAM, which stands for ‘separation by minimum overlapping method’. This method can be applied when two spectra of the same sample consisting of two species can be recorded. These spectra have to differ in composition but total concentration has to maintain constant. In other words, the data required to apply the method comes from one sample for which the two spectra were recorded at two different points of time (the composition of the sample has to change). Knowledge of real fractions found in the crude plots is sufficient to extract quantitatively the spectra of pure components. This new simple method was successfully tested on simulated spectra and then applied to a real problem.     

Composition of essential oil from <Emphasis Type="Italic">Artemisia glauca</Emphasis> from western Siberia

The composition of essential oil from Artemisia glauca (Asteraceae) growing in southern Siberia was studied. More than 60 oil components consisting of 99.0–99.7% of the total volatile components were identified by GC—MS by comparison of full mass spectra and retention times. The main components of the essential oil were acetylene derivatives of capillene (11–60%) and benzyldiacetylene (1–31%). Other acetylene derivatives such as capillin, (E)-hex-4-en-2-ynylbenzene, 1-(4-methoxyphenyl)-2,4-pentadiyne, and capillarin were also identified in the oil. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 446–449, September–October, 2007.     

Analogs of pyrimidine nucleosides. 20. Aminomethylation of 5-fluorouracil and thymine

Reactions were studied of 5-fluorouracil and thymine with formaldehyde and secondary amines (piperidine, morpholine) and also of their 2,4-bis(trimethylsilyl) derivatives with N-methoxymethylmorpholine and bis(amino)methanes. The N-aminomethylation products are slightly stable and in aqueous solutions decompose readily to the starting components; their structure was confirmed by PMR spectra.For Communication 19, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 90–93, January, 1987.     

Calibration transfer of near‐infrared spectra for extraction of informative components from spectra with canonical correlation analysis

A new calibration transfer method that applies canonical correlation analysis (CCA) to transfer the informative components extracted from a spectral dataset is proposed to reduce the interference of noise, background and non‐predicted properties. This method employs the partial least squares method to extract the informative components related to the predicted properties from the raw spectra and then corrects the informative components based on CCA. The performance of this algorithm was tested using three pairs of spectra batches: two pairs of corn spectra and one pair of tri‐component solvent spectra. The results showed that this method can significantly reduce prediction errors compared with CCA and piecewise direct standardization. Copyright © 2014 John Wiley & Sons, Ltd.     

Standardless multicomponent qNMR analysis of compounds with overlapped resonances based on the combination of ICA and PULCON

A fast and reliable nuclear magnetic resonance (NMR) method for quantitative analysis of targeted compounds with overlapped signals in complex mixtures has been established. The method is based on the combination of chemometric treatment for spectra deconvolution and the PULCON principle (pulse length based concentration determination) for quantification. Independent component analysis (ICA) (mutual information least dependent component analysis (MILCA) algorithm) was applied for spectra deconvolution in up to six component mixtures with known composition. The resolved matrices (independent components, ICs and ICA scores) were used for identification of analytes, calculating their relative concentrations and absolute integral intensity of selected resonances. The absolute analyte concentrations in multicomponent mixtures and authentic samples were then calculated using the PULCON principle. Instead of conventional application of absolute integral intensity in case of undisturbed signals, the multiplication of resolved IC absolute integral and its relative concentration in the mixture for each component was used. Correction factors that are required for quantification and are unique for each analyte were also estimated. The proposed method was applied for analysis of up to five components in lemon and orange juice samples with recoveries between 90% and 111%. The total duration of analysis is approximately 45 min including measurements, spectra decomposition and quantification. The results demonstrated that the proposed method is a promising tool for rapid simultaneous quantification of up to six components in case of spectral overlap and the absence of reference materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Selective removal of interference signals for near-infrared spectra of biomedical samples by using region orthogonal signal correction

New approach for chemometrics algorithm named region orthogonal signal correction (ROSC) has been introduced to improve the predictive ability of PLS models for biomedical components in blood serum developed from their NIR spectra in the 1280-1849 nm region. Firstly, a moving window partial least squares regression (MWPLSR) method was employed to locate the region due to water as a region of interference signals and to find the informative regions of glucose, albumin, cholesterol and triglyceride from NIR spectra of bovine serum samples. Next, a novel chemometrics method named searching combination moving window partial least squares (SCMWPLS) was used to optimize those informative regions. Then, the specific regions that contained the information of water, glucose, albumin, cholesterol and triglyceride were obtained. When an interested component in the bovine serum solution, such as glucose, albumin, cholesterol or triglyceride is being an analyte, the other three interests and water are considered as the interference factors. Thus, new approach for ROSC has employed for each specific region of interference signal to calculate the orthogonal components to the concentrations of analyte that were removed specifically from the NIR spectra of bovine serum in the region of 1280-1849 nm and the highest interference signal for model of analyte will be revealed. The comparison of PLS results for glucose, albumin, cholesterol and triglyceride built by using the whole region of original spectra and those developed by using the optimized regions suggested by SCMWPLS of original spectra, spectra treated OSC for orthogonal components of 1-3 and spectra treated ROSC using selected removing the highest interference signals from the spectra for orthogonal components of 1-3 are reported. It has been found that new approach of ROSC to remove the highest interference signal located by SCMWPLS improves of the performance of PLS modeling, yielding the lower RMSECV and smaller number of PLS factors.     

DFT and ab initio study of structure of dyes derived from 2-hydroxy and 2,4-dihydroxy benzoic acids

We present a detailed analysis of the structural, infrared spectra and visible spectra of a series of azo dyes preparation of salicylic acid and 2,4-dihydroxy benzoic acid derivatives as the coupling component. The preparation of these azo dyes with salicylic acid and 2,4-dihydroxy benzoic acid derivatives (salicylic acid, methyl salicylate, ethyl salicylate, butyl salicylate, methyl 2,4-dihydroxy benzoate, ethyl 2,4-dihydroxy benzoate, salicylaldehyde, salicylamide, 2,4-dihydroxy benzamide, salicylaldoxime) have been investigated theoretically by performing HF and DFT levels of theory using the standard 6-31G* basis set. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from solid phase FT-IR spectra are assigned modes based on the results of the theoretical calculations. The observed spectra are found to be in good agreement with the calculations.     

Weighted two-band target entropy minimization for the reconstruction of pure component mass spectra: Simulation studies and the application to real systems

A method is proposed, on the basis of a recently developed algorithm--Band Target Entropy Minimization (BTEM)--to reconstruct mass spectra of pure components from mixture spectra. This method is particular useful in dealing with spectral data with discrete features (like mass spectra). Compared to the original BTEM, which has been applied to differentiable spectroscopies such as Fourier-transfer infrared spectroscopy (FTIR), ultraviolet (UV), Raman, and nuclear magnetic resonance (NMR), the latest modifications were obtained through: (1) Reformulating the objective function using the peak heights instead of their derivatives; (2) weighting the abstract vector VT to reduce the effect of noise; (3) using a two-peak targeting strategy (tBTEM) to deal with strongly overlapping peaks; and (4) using exhaustive search to locate all the component spectra. A set of 50 multi-component mass spectra was generated from ten reference experimental pure component spectra. Many of the compounds chosen have common MS fragments and therefore, many of the pure component spectra have considerable intensity in same data channels. In addition, a set of MS spectra from a real system with four components was used to examine the newly developed algorithm. Successful reconstruction of the ten component spectra of the simulated system and the four component spectra of the real system was rapidly achieved using the new tBTEM algorithm. The advantages of the new algorithm and its implication for rapid system identification of unknown mixtures are readily apparent.     

Application of band-target entropy minimization (BTEM) and residual spectral analysis to in situ reflection-absorption infrared spectroscopy (RAIRS) data from surface chemistry studies

The band-target entropy minimization (BTEM) curve resolution technique has been used to analyze in situ reflection-absorption infrared spectroscopy (RAIRS) data of CO chemisorption on Ni(1 1 1) single crystal surfaces. The bilinearity assumption for pRAIRS data, that is, negative logarithm to the base 10 of raw reflectance RAIRS data, was found to be sufficiently valid for the test data. A total of 11 real pure component pRAIRS spectra were elucidated via BTEM in tandem with an iterative residual spectral data analysis. Furthermore, 2 abstract pure component right singular vectors were found to account for all the pRAIRS non-linearities, baseline drifts and other spectral noise. In total, 100.2% of the pRAIRS signals were accounted for by these 13 spectral components. The 11 real pure component pRAIRS spectra and their corresponding relative concentration kinetic sequences correlate with 6 well-known adsorbed CO domain structures. Moreover, amongst the BTEM resolved spectra were five new bands that were not previously observed using conventional visual identification methods adopted by surface chemists. These new bands engendered new understanding to the mechanism of CO chemisorption on Ni(1 1 1). The combination of BTEM with residual spectral analysis was thus demonstrated to be efficacious for curve resolution of in situ RAIRS data obtained from surface chemistry studies.     

Electronic spectra and structure of 2,4-dihalopicolines and their N-oxides

UV spectra of 2,4-dihalopicolines and their N-oxides are presented, and the influence of substituents on spectral parameters is discussed. The electronic spectra were calculated by a modified INDO method. Transition energies, intensities, and assignments were compared with UV spectra. The degree of intramolecular charge transfer in 2,4-dihalopicolines is greater than in 2-halopicoline N-oxides and smaller than in 2-halo-4-nitropicoline N-oxides. Difference values of HOMO-LUMO energies point out that the susceptibility on photochemical reaction lies in the order: 2-halo-4-nitropicoline N-oxides > 2,4-dihalopicoline N-oxides > 2-halopicoline N-oxides > pyridine N-oxide. Department of Organic Chemistry, University of Economics, PL-53-342 Wroclaw, Poland. Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 34, No. 10, pp. 1352–1366, October, 1999.     

Mass spectra of piperidine dicarboxylic acids and their esters

Electron impact mass spectra of the epimers of 2,4-, 2,5-, and 2,6-piperidine dicarboxylic acids and their methyl esters and N-acyl derivatives have been studied. Data from DADI spectra have been used to establish the basic fragmentation paths. Chemical ionization spectra of positive and negative ions of 2,4- and 2,5-piperidine dicarboxylic acids are described.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1490–1495, November, 1986.     

Characterization of radix rehmanniae processing procedure using FT-IR spectroscopy through nonnegative independent component analysis

A method is proposed for monitoring the radix rehmanniae proparate processing procedure and determining the endpoint of the process using attenuated total reflectance (ATR) FT-IR through nonnegative independent component analysis (ICA). In the proposed method, ATR FT-IR spectra of the samples were firstly measured at different steaming periods. Then, nonnegative ICA was used for direct estimation of the feature spectra of the pure components in the mixture without pre-separation and other prior information. The estimated independent components (ICs) and their variation of the relative concentrations were used to characterize the processing procedure and determine the endpoint. The results show that the estimated three ICs are consistent with that of the chemical components in the mixtures, i.e. catalpol/rehmaionoside, glucose, and other compounds that nearly keep invariant during the processing procedure. The endpoint determined by the IR-ICA method is 15 h, which was located in the range obtained by expert sensory analysis, whereas the endpoint determined by the traditional sensory analysis is 14 ∼ 17 h and even 14 ∼ 20 h, which showed the significant deviation of the endpoints determined by different operators. Figure Characterisation of radix rehmanniae processing procedure using FT-IR spectroscopy through nonnegative independent component analysis     

Structure of native and regenerated cellulose as revealed by proton NMR analysis

Differences in fiber structure between cotton and cuprammonium rayon are studied by a refined broad-line proton NMR analysis of samples swollen with deuterated dimethyl sulfoxide, which has no effect on the spectra but enhances differences in molecular mobility between crystalline and noncrystalline regions. The spectra obtained are decomposed into four components: broad, medium, narrow, and extremely narrow. These components are identified as contributions, respectively, from crystalline and rigid noncrystalline (frozen glassy) material, a noncrystalline glassy component exhibiting local segmental motion, a noncrystalline rubbery component exhibiting liquidlike molecular motion, and protons included in DMSO-d₆ as an impurity. The mass fraction of the narrow component in cotton was about 0.01, whereas it was as high as 0.18 in cuprammonium rayon. It is concluded that even in the swollen state, native cellulose is devoid of a liquidlike mobile component, but regenerated cellulose contains a considerable amount of a noncrystalline component involving liquidlike segmental motion of molecules.     

Determination of 2,4-dichlorophenol in dichlorophenol isomers by NMR

Quantitative analysis of isomers by NMR has been carried out in the measurement of species whose components present simple and sufficiently isolated spectra. Generally, the substituted aromatic proton splits into complicated spectral lines due to spin-spin coupling. The ring proton spectra of dichlorophenol isomers show a pattern peculiar to the three spin system. It was found that some of the signal attributable to these compounds appear in a position slightly isolated from each other. Therefore, we established the quantitative analysis method for dichlorophenol, using the signal intensity method. From the result of the quantitative analysis, the lowest detectable concentration was 1·1% (±0·3% at the standard deviation). The accuracy of the peak intensity method was found to be ±1·8% within the 50 to 80 mol% concentration range of 2,4-dichlorophenol isomer.     

Enhanced target factor analysis

Target testing or target factor analysis, TFA, is a well-established soft analysis method. TFA answers the question whether an independent target test vector measured at the same wavelengths as the collection of spectra in a data matrix can be excluded as the spectrum of one of the components in the system under investigation. Essentially, TFA cannot positively prove that a particular test spectrum is the true spectrum of one of the components, it can, only reject a spectrum. However, TFA will not reject, or in other words TFA will accept, many spectra which cannot be component spectra. Enhanced Target Factor Analysis, ETFA addresses the above problem. Compared with traditional TFA, ETFA results in a significantly narrower range of positive results, i.e. the chance of a false positive test result is dramatically reduced. ETFA is based on feasibility testing as described in Refs. [16–19]. The method has been tested and validated with computer generated and real data sets.     

Thermal Studies of New Cu(I) and Ag(I) Complexes with Bipyridine Isomers

The complexes of the general formula MLSCN (M=Cu(I), Ag(I), L=2,2′-bipyridine=2-bipy, 4,4′-bipyridine=4-bipy or 2,4′-bipyridine=2,4′bipy) have been prepared and their IR spectra examined. The nature of metal-ligand coordination is discussed. Thermal decomposition in air of these complexes occurred in several successive endothermic and exothermic processes and the residue was Cu₂O and Ag, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimation of component spectra by the principal components method

The principal components method enables component spectra from pigment mixtures to be estimated by evaluating the eigenvectors of the second moment matrix. The components are linear combinations of these eivenvectors, but cannot be identified unambiguously. With the conditions of non-negativity of spectral values and of concentrations, this ambiguity can be limited; components spectra for 2 and 3 components were calculated earlier. In the present work, maximal dissimilarity of component spectra is assumed as a further condition. An algorithm based on linear programming is described; it enables any number of components to be estimated from eigenvectors of the second moment matrix with better reliability than previously.     

Enhancement of photoelectric catalytic activity of TiO2 film via Polyaniline hybridization

A Polyaniline (PANI)/TiO₂ film coated on titanium foil was successfully prepared using the sol-gel method followed by a facile chemisorption. Compared with pristine TiO₂, the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation rates of 2,4-dichlorophenol (2,4-DCP) with the PANI/TiO₂ film were enhanced by 22.2% and 57.5%, respectively. 2,4-DCP can be mineralized more effectively in the presence of PANI/TiO₂ film. The best PEC degradation efficiency of 2,4-DCP with the PANI/TiO₂ film was acquired at an external potential of 1.5 V with a layer of 1 nm thick PANI. The PANI/TiO₂ film was characterized by Raman spectra, Fourier transform infrared spectra (FT-IR), Auger electron spectroscopy (AES), and electrochemical analysis. These results indicated that there was a chemical interaction on the interface of PANI and TiO₂. This interaction may be of significance to promote the migration efficiency of carriers and induce a synergetic effect to enhance the PC and PEC activities.