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.     

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.     

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.     

Attempts at Solvolytic Generation of Phenyl Cations

New substrates and reaction conditions which may be expected to yield phenyl cation intermediates have been investigated. The approaches used were: (a) solvolysis of PhX in fluorinated alcohols, where X = ? N (O) = NOTs (tosyloxyazoxy), ? N (O) = NONf (Nf = C₄F₉SO) and ? OSO₂\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document} (CH₃)₃ōTf (Tf=CF₃SO); (b) solvolysis of ArBr, PhOTf and PhOSO₂\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm + } $\end{document}(CH₃)₃ōTf (phenyl ‘betylate triflate’) in super-acid solvents (FSO₃H · SbF₅, SbF₅, AgSbF₆). Analysis of the product mixtures provided no evidence for the intermediacy of phenyl cations as a major pathway in any of the reactions. This result is remarkable, since the ‘betylate’, for example, is a better leaving group by a factor of at least 10⁵ than the ‘super’ leaving group triflate in the solvolysis of alkyl sulfonates. These results are a further indication of the extremely low stability of phenyl cations, as well as of the very special properties of the nitrogen leaving group in arenediazonium ions.     

Isolation of an inclusion complex of naphthol and its benzoate as an intermediate in the solvent-free benzoylation reaction of naphthol

Solvent-free benzoylation of naphthol was found to proceed via an inclusion complex intermediate of the naphthol and its benzoate by IR spectral monitoring.     

Dediazoniation of Arenediazonium Ions in Homogeneous Solution. Part XII. Solvent effects in competitive heterolytic and homolytic dediazoniations

In heterolytic dediazoniations arenediazonium salts form aryl cations. The reaction rates are relatively slow; they depend only to a small extent on the solvent. It is shown that the solvents in which the heterolytic dediazoniation mechanism is predominant have a low nucleophilicity, whereas in solvents of high nucleophilicity homolysis of arenediazonium salts, i.e. the formation of aryl radicals and related intermediates, is favoured. Under comparable conditions, homolytic rates are faster than the corresponding rates of heterolysis. Homolysis is strongly enhanced by addition of nucleophiles which form relatively stable radicals by electron transfer. The ability of additives to catalyze homolysis of arenediazonium salts can be explained using the concept of a nucleofugic

1 In the original proposal [32] we used the word nucleofugal. In keeping with a forthcoming proposal on nomenclature in physical organic chemistry by Commission III.2 (Physical Organic Chemistry) of IUPAC we now use the word nucleofugic.

homolytic leaving group.     

Optimization of the direct LSC method for determination of biogenic component in liquids by applying 14C

Journal of Radioanalytical and Nuclear Chemistry - Determination of fraction of biogenic component in liquid fuels by a direct radiocarbon measurement in liquid scintillation counter (direct-LSC...     

Lyapunov–Razumikhin method for impulsive functional differential equations and applications to the population dynamics

The present paper deals with the investigation of the stability of the zero solution of impulsive functional differential equations. By means of piecewise continuous functions coupled with the Razumikhin technique sufficient conditions for stability, uniform stability and asymptotic stability of the zero solution of such equations are found.     

Reactivity of Carbenes and Related Compounds towards Molecular Nitrogen

The thermal N₂ exchange of a number of ¹⁵N-labelled diazo compounds was studied in solution. The compounds involved were 3-diazo-1-methylindolin-2-one ( 1 ), 9-diazofluorene ( 2 ), 5-diazo-1,3-cyclopentadiene-1,2,3,4-tetracarbonitrile ( 3 ), 2-diazo-2H-imidazole-4,5-dicarbonitrile ( 4 ), 4-diazocyclohexa-2,5-dienone ( 5 ), and the conjugate acids of 4 and 5 , namely 4,5-dicyano-1H-imidazole-2-diazonium ion ( 6 ) and 4-hydroxybenzenediazonium ion ( 7 ). Only 1 , 4 , 6 , and 7 exchange their diazo group with ‘external’ molecular N₂. The results are explained on the hypothesis that only organic species which have an empty σ orbital and which are effective in π electron back-donation are able to react with N₂. Thus, reaction with carbenes is likely to occur only if the carbene is in the ¹A₂ singlet state and if its electrophilicity is high.