Determination of nitrated polycyclic aromatic hydrocarbons and their precursors in biotic matrices

Analytical method for the determination of ultra-trace levels of nitro-PAHs in various biotic matrices has been developed. Soxhlet extraction and/or solvent extraction enhanced by sonication were used for isolation of target analytes; GPC followed by SPE were employed for purification of crude extracts. GC-MS/NCI technique was utilised for identification/quantitation of target analytes. Performance characteristics of implemented method were obtained through thorough in-house validation procedure. The main sources of uncertainties were critically evaluated, possible strategies of their elimination/minimisation were considered and consequently employed. Examination of real-life samples of various foodstuffs (complete human diet, mate tea, pumpkin seed oil, parsley, sausages) was performed in this study.     

On-line preconcentration of weak electrolytes by electrokinetic accumulation in CE: experiment and simulation

A new on-line preconcentration technique was developed that makes possible to determine nanomolar concentrations of weak acidic analytes in CE. The method consists of long-running electrokinetic sample injection and stacking (electrokinetic immobilization) of the analytes at a boundary of two electrolytes with different pH values (pH 9.5 and 2.5) and consequent mobilization of the stacked uncharged analytes in a micellar system (containing SDS micelles). Several factors including buffer concentration, pH, applied voltage, time of preconcentration, and SDS concentration were tested to optimize the analysis method. An about 4600-fold increase of the sample concentration (in comparison with the standard CZE) can be achieved during the preconcentration step. Two preservatives applied in food industry -- benzoic acid and sorbic acid were used as model samples. The applicability of the proposed method in food analysis was demonstrated by determination of nanomolar concentrations of benzoic acid in sunflower oil. An extended version of the computer program Simul was used for modeling both the preconcentration and mobilization processes taking place in the capillary.     

Mn2+ complexes of 1-oxa-4,7-diazacyclononane based ligands with acetic, phosphonic and phosphinic acid pendant arms: stability and relaxation studies

A new class of macrocyclic ligands based on 1-oxa-4,7-diazacyclononane was synthesized and their Mn(2+) complexes were investigated with respect to stability and relaxation properties. Each ligand has two pendant arms involving carboxylic (H(2)L(1)--1-oxa-4,7-diazacyclononane-4,7-diacetic acid), phosphonic (H(4)L(2)--1-oxa-4,7-diazacyclononane-4,7-bis(methylenephosphonic acid)), phosphinic (H(2)L(3)--1-oxa-4,7-diazacyclononane-4,7-bis(methylenephosphinic acid)) or phenylphosphinic (H(2)L(4)--1-oxa-4,7-diazacyclononane-4,7-bis[methylene(phenyl)phosphinic acid]) acid moieties. H(2)L(3) and H(2)L(4) were synthesized for the first time. The crystal structure of the Mn(2+) complex with H(2)L(4) confirmed a coordination number of 6 for Mn(2+). The protonation constants of all ligands and the stability constants of their complexes with Mn(2+) and some biologically or biomedically relevant metal ions were determined by potentiometry. The protonation sequence of H(2)L(3) was followed by (1)H and (31)P NMR titration and the second protonation step was attributed to the second macrocyclic nitrogen atom. The potentiometric data revealed a relatively low thermodynamic stability of the Mn(2+) complexes with all ligands investigated. For H(2)L(3) and H(2)L(4), full Mn(2+) complexation cannot be achieved even with 100% ligand excess. The transmetallation of MnL(1) and MnL(2) with Zn(2+) was too fast to be followed at pH 6. Variable temperature (1)H NMRD and (17)O NMR measurements have been performed on MnL(1) and MnL(2) to provide information on water exchange and rotational dynamics. The (17)O chemical shifts indicate hydration equilibrium between mono- and bishydrated species for MnL(1), while MnL(2) is monohydrated. The water exchange is considerably faster on MnL(1) (k(ex)(298) = 1.2 × 10(9) s(-1)) than on MnL(2) (k(ex)(298) = 1.2 × 10(7) s(-1)). Small endogenous anions (phosphate, carbonate, citrate) do not replace the coordinated water in either of the complexes, but they induce their slow decomposition. All Mn(2+) complexes are stable toward air-oxidation.     

Activated oxygen is formed by the mycelium and is involved mainly in the primary attack of LCC byP. chrysosporium

Convincing evidence demonstrating the involvement of activated forms of oxygen in the fungal degradation of LCC have been obtained by different research groups. Among the most active intermediates stands ·OH, which is the subject of this work. We describe here a method for the accurate detection of ·OH based on the specific decarboxylation of benzoic acid. Using this method, we have demonstrated that the decarboxylating system is not diffusible in the culture medium, but is strongly associated with the mycelium. The 6-d-old fungus is able to form ·OH even after transferring to new medium. Cell wall fractions were not able to decarboxylate benzoate. Another topic that has been considered is the role of hydroxyl radical in LCC degradation. In agreement with others, we have established that ·OH scavengers severely inhibit the degradation fo LCC when added to the cultures. If LCC was pretreated by chemically generated ·OH, it turns out thatP. chrysosporium is able to use the solubilized fractions. However, in contrast to that of “native LCC” the metabolization of the solubilized moiety of LCC was not inhibited by -OH scavengers. It is concluded that -OH may act only during the primary attack on LCC and not during the course of its subsequent degradative pathway.     

Laser ablation doping of poly crystalline tin dioxide films with palladium

Laser ablation of palladium was studied and velocity (energy) distributions of palladium ions evaporated by an Kr-F laser in a vacuum were obtained. The optimum values of energy fluence (fluence rate) of laser radiation for doping tin dioxide films, at which neither multiply charged Pd^N+ ions nor ionized clusters Pd _N ⁺ , occur in a plasma, were determined. From time-of-flight probe measurement data, Pd⁺ implantation depths in SnO₂ films were calculated, which qualitatively agree with the results obtained by secondary neutral mass spectrometry. Electric conductivity measurements on the obtained films in a gas phase showed that introduction of palladium into polycrystalline SnO₂ films by laser ablation significantly enhanced their gas sensitivity to hydrogen.     

Das Atomgewicht des Ceriums

Ohne Zusammenfassung