Tailoring the electrochemical charge storage properties of carbonaceous support by redox properties of heteropoly acids: where does the synergy come from?

Journal of Solid State Electrochemistry - The synergistic effects between two Keggin-type heteropoly acids (HPAs) and carbon surface were examined and elucidated. An improved high rate capability...     

Concentration factors for 226Ra in the mullet (Mugilidae) species Mugil cephalus from the South Adriatic Sea

²²⁶Ra activity concentration in the mullet (Mugilidae) species Mugil cephalus whole individuals, and some organs (gills, gastrointestinal system, fins, muscle and bones), was measured by the γ-coincidence spectrometer PRIPYAT-2M. ²²⁶Ra transfer parameters [concentration factors (CFs)] from seawater, sediment and mud with detritus to fish tissues, and annual intake by humans consuming this fish species, have been estimated. Minimum detected radium activity concentration in whole M. cephalus individuals was found to be 0.89 ± 0.42 to 3.09 ± 0.41 Bq kg⁻¹, with arithmetic mean of 1.65 ± 0.39 Bq kg⁻¹. An average concentration in muscles is found to be 2.28 ± 0.84 Bq kg⁻¹, in gills—5.02 ± 1.85 Bq kg⁻¹, in gastrointestinal system—12.88 ± 1.71 Bq kg⁻¹, and in bones—14.72 ± 3.75 Bq kg⁻¹. No one fins showed radium activity above minimum detectable one. Annual intake of ²²⁶Ra by human consumers of this fish species is estimated to provide an effective dose of 0.006 mSv year⁻¹. CFs for ²²⁶Ra indicating transfer from seawater to whole individuals ranged from 8.9 to 30.9, and those indicating transfer from the sediment and mud with detritus—from 0.11 to 0.39 and from 0.08 to 0.3, respectively. The seawater to bones CFs varied from 97.9 to 197.3, to gastrointestinal system—from 59 to 178.8, to gills—from 22.5 to 68.3, to muscles—from 17 to 30.8.     

Polycarboxylic microsphere polymer gel for solid phase extraction of trace elements

A simple and sensitive method has been developed for the determination of trace elements (Cd, Co, Cu, Ni, Fe and Pb) in sea water and natural waters by electrothermal atomic absorption spectrometry. The method is based on column solid phase extraction of trace elements on a newly synthesized polycarboxylic gel. The sorbent was prepared by dispersion copolymerization of methacrylic acid (as a monomer) and trimethylolpropane trimethacrylate (as a crosslinking agent) in the form of monodisperse microspheres. It exhibits high regeneration ability, chemical and mechanical resistivity. The influence of pH, flow rates and concentration of the eluent on the degree of sorption of trace elements have been evaluated. The maximum static adsorption capacities of the sorbent at the optimal conditions for lead, nickel, cobalt, iron, cadmium and copper are determined. Detection limits achieved for the elements studied for 100 mL water sample volume were between 0.005 and 0.05 μg L^?1. The relative standard deviation varied in the range 5–13% for all elements studied. The validity of the method was checked by an analysis of standard reference material SRLS-3 Riverine Water. Very good agreement between the analytical results and the certified values (t-test at 95% confidence level) was observed. The new polycarboxylic gel was applied to passive sampling procedures due to its high chemical and mechanical stability.     

Ion-imprinted polymethacrylic microbeads as new sorbent for preconcentration and speciation of mercury

Metal ion-imprinted polymer particles have been prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as cross-linking agent and 2,2′-azobisisobutyronitrile as initiator, in the presence of Hg(II)-1-(2-thiazolylazo)-2-naphthol complex. The separation and preconcentration characteristics of the Hg-ion-imprinted microbeads for inorganic mercury have been investigated by batch procedure. The optimal pH value for the quantitative sorption is 7. The adsorbed inorganic mercury is easily eluted by 2 mL 4 M HNO₃. The adsorption capacity of the newly synthesized Hg ion-imprinted microbeads is 32.0 μmol g⁻¹ for dry copolymer. The selectivity of the copolymer toward inorganic mercury (Hg(II)) ion is confirmed through the comparison of the competitive adsorptions of Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Zn(II)) and high values of the selectivity and distribution coefficients have been calculated. Experiments performed for selective determination of inorganic mercury in mineral and sea waters showed that the interfering matrix does not influence the extraction efficiency of Hg ion-imprinted microbeads. The detection limit for inorganic mercury is 0.006 μg L⁻¹ (3σ), determined by cold vapor atomic adsorption spectrometry. The relative standard deviation varied in the range 5-9 % at 0.02-1 μg L⁻¹ Hg levels. The new Hg-ion-imprinted microbeads have been tested and applied for the speciation of Hg in river and mineral waters: inorganic mercury has been determined selectively in nondigested sample, while total mercury e.g. sum of inorganic and methylmercury, has been determined in digested sample.     

Explicit–implicit mapping approach to nonlinear blind separation of sparse nonnegative dependent sources from a single mixture: pure component extraction from nonlinear mixture mass spectra

The nonlinear, nonnegative single‐mixture blind source separation problem consists of decomposing observed nonlinearly mixed multicomponent signal into nonnegative dependent component (source) signals. The problem is difficult and is a special case of the underdetermined blind source separation problem. However, it is practically relevant for the contemporary metabolic profiling of biological samples when only one sample is available for acquiring mass spectra; afterwards, the pure components are extracted. Herein, we present a method for the blind separation of nonnegative dependent sources from a single, nonlinear mixture. First, an explicit feature map is used to map a single mixture into a pseudo multi‐mixture. Second, an empirical kernel map is used for implicit mapping of a pseudo multi‐mixture into a high‐dimensional reproducible kernel Hilbert space. Under sparse probabilistic conditions that were previously imposed on sources, the single‐mixture nonlinear problem is converted into an equivalent linear, multiple‐mixture problem that consists of the original sources and their higher‐order monomials. These monomials are suppressed by robust principal component analysis and hard, soft, and trimmed thresholding. Sparseness‐constrained nonnegative matrix factorizations in reproducible kernel Hilbert space yield sets of separated components. Afterwards, separated components are annotated with the pure components from the library using the maximal correlation criterion. The proposed method is depicted with a numerical example that is related to the extraction of eight dependent components from one nonlinear mixture. The method is further demonstrated on three nonlinear chemical reactions of peptide synthesis in which 25, 19, and 28 dependent analytes are extracted from one nonlinear mixture mass spectra. The goal application of the proposed method is, in combination with other separation techniques, mass spectrometry‐based non‐targeted metabolic profiling, such as biomarker identification studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Gas‐phase tautomerism in hydroxy azo dyes – from 4‐phenylazo‐1‐phenol to 4‐phenylazo‐anthracen‐1‐ol

The tautomeric constants of a series of azo dyes were estimated in the gas phase by using electron ionization mass spectrometry. It was shown that the relative amount of the keto tautomer increases from 4‐phenylazo‐1‐phenol to 4‐phenylazo‐anthracen‐1‐ol, thus confirming the quantum‐chemical predictions. The existence of the enol tautomer of 4‐phenylazo‐anthracen‐1‐ol is shown for the first time by mass spectrometry in the gas phase. This finding is supported by flash photolysis measurements in solution. Copyright © 2010 John Wiley & Sons, Ltd.     

Almost periodic solutions for impulsive neural networks with delay

In the present paper the problems of existence and uniqueness of almost periodic solutions for impulsive cellular neural networks with delay are considered.     

Study of interactions of concentrated marine dissolved organic matter with copper and zinc by pseudopolarography

The interaction of dissolved organic matter (DOM) with copper and zinc in a concentrated seawater sample was characterised by pseudopolarography. Measurements performed at increased concentrations of copper(II) ions showed successive saturation of active DOM sites which indicate possible partition of copper between (i) free or labile complexes, (ii) reduced and released within the potential window of the method, and (iii) electroinactive copper complexes. Pseudopolarograms measured at pH 4 indicate a release of copper which was bound to the active sites of DOM that formed non-labile complexes. Variation of the peak position and half-peak width along the scanned deposition potentials and with the increasing concentration of copper bear the information about the complex electrochemical processes at the electrode surface and in the bulk of the solution. Pseudopolarograms of zinc showed a strong dependence of the peak current and the peak position along the scanned deposition potentials on pH values, indicating preferentially complexation of zinc with carboxylic-like active sites of DOM in the measured sample. Pseudopolarography is a valuable method in the trace metal complexation and speciation studies, serving as a fingerprint of the analysed sample.