Zoltán Galbács

Alkali-induced decomposition of hydrogen peroxide

It has been shown that iron(III), copper(II), and manganese(II), common contaminants of alkali-metal hydroxides, not only enhance the rate of alkali-induced decomposition of hydrogen peroxide, but also result in the rate maximum being observed at a different pH value of 11.6, 12.0, and 9.5, respectively. Different methods are recommended for the production of high-purity alkali solution and removal of contaminants. The addition of ethylenediaminetetra-acetic acid (H4edta) to the reaction mixture resulted in a further decrease in the decomposition rate and three stages could be distinguished in the rate vs. time curves. The lowest rate (stage II) is proportional to the square of the hydrogen peroxide concentration and to the hydroxide-ion concentration. During this stage, formation of hydroxyl and superoxide radicals was observed. It is believed that the true rate of the alkali-induced decomposition of hydrogen peroxide can be determined if purified alkali and chelating agent are simultaneously employed: the rate coefficient is 3 × 10–6 dm3 mol–1 s–1 at pH 11.6, 10–3 mol dm–3 H4edta, and 0.1 mol dm–3 H2O2 at 308 K.

Peroxide derivatives of molybdenum(VI) in neutral and alkaline media

SummaryThe peroxidation of molybdenum(VI) was investigated in neutral and alkaline media. The stability constants of the peroxo complexes were determined by spectrophotometric measurement as (9.12±0.67)×10−7, (2.68±0.17) ×105, (1.26±0.06)×106 and (1.58±0.02) for the 1∶1, 2∶1 (yellow), 3∶1 and 4∶1 (red) species. The diperoxomolybdate disproportionates into the tetraperoxo derivative when treated with alkali. Formation of the tetraperoxo complex was found to be pH dependent according to a curve, with maximum at pH 10. Acidification of tetraperoxomolybdate solution results in the regeneration of hydrogen peroxide and the diperoxo complex is reformed.

Optimalisation of Magnesium Ammonium Phosphate Precipitation and its Applicability to the Removal of Ammonium

Among the physico-chemical abatement technologies, mainly acid scrubbers have been used to control NH3-emission. The disadvantage of this technique is that it yields waste water, highly concentrated in ammonia. In this report, the applicability of the magnesium ammonium phosphate (MAP) process to regenerate the liquid phase, produced by scrubbing NH3-loaded waste gases, was investigated. In the MAP process, ammonium is precipitated as magnesium ammonium phosphate, which can be used as a slow release fertilizer. The influence of a number of parameters, e.g. pH, kinetics, molar ratio NH(+)4/Mg2+/PO(3-)4 on the efficiency of the formation of MAP and on the ammonium removal efficiency was investigated. In this way, optimal conditions were determined for the precipitation reaction. Next to this, interference caused by other precipitation reactions was studied. At aqueous NH(+)4-concentrations of about 600 mg l(-1), ammonium removal efficiencies of 97% could be obtained at a molar ratio NH(+)4/Mg2+/PO(3-)4 of 1/1.5/1.5. To obtain this result, the pH was continuously adjusted to a value of 9 during the reaction. According to this study, it is obvious that the MAP-precipitation technology offers opportunities for ammonium removal from scrubbing liquids. The practical applicability of the MAP-process in waste gas treatment systems, however, should be the subject for further investigations.

Chronic low-dose maternal exposure to methylmercury enhances epileptogenicity in developing rats

Effects of continuous low‐dose maternal methylmercury intoxication on the induction and propagation of ictal epileptiform activity induced by 3‐aminopyridine, were investigated on the neocortex of 4‐weeks‐old offspring rats. Epileptogenicity was significantly increased in offspring of mercury‐treated animals compared to those of controls, characterized by more frequent occurrence of periodic ictal activity, a facilitated propagation of epileptiform discharges and a strong tendency to generalization. The latency of first ictal event was slightly shorter and the average duration of individual ictal periods slightly longer in treated animals. However, the amplitude of seizure discharges was significantly smaller in treated animals than in controls.

Slurry nebulization ICP-AES spectrometry method for the determination of tin in organotin(IV) complexes

This paper proposes a quick, novel method for tin determination in organotin chemicals by slurry nebulization inductively coupled plasma atomic emission (ICP-AES) spectrometry. The method was tested by the measurement of five organotin carboxylate complexes of known composition for obtaining simple stoichiometric data. The slurries were prepared by first dissolving the organotins in an adequate solvent (methanol, pyridine or acetone) well miscible with water and then adding this solution drop-by-drop to a 0.005% TX-100 tenzide solution while maintaining intensive mixing. Dynamic laser light scattering experiments showed that the average equivalent particle size in the resulting slurry was approximately 0.3 mum for all samples and solvents. Under suitable ICP-AES measuring conditions, the signal recoveries were found to be between 101.8 and 106.6%, which allowed direct nebulization and calibration against aqueous solutions. Typically, 70 mug l(-1) detection limit and 1-5% relative S.D. on five replicates can be achieved by the described method.

Generation of superoxide radicals in alkaline solutions of hydrogen peroxide and the effect of superoxide dismutase in this system

Abstract It is shown that alkaline peroxide cannot serve as a source of superoxide radicals without the presence of a catalyst. Addition of superoxide dismutase to alkaline hydrogen peroxide solution results in an immediate drop in the concentration of superoxide radicals, followed by an increase in the radical yield, because the enzyme is attacked by OH radicals and transformed into an active (but dismutase-inactive) catalyst of hydrogen peroxide decomposition.

Calcium, magnesium and zinc ion coordination equilibria of vincristine

The zinc ion coordination of vincristine was studied by polarography; the analogous calcium ion coordination process was studied potentiometrically by a calcium ion selective electrode. In both cases, complexes of 1:1 composition were formed. The formation constant of the calcium complex was found to be 1g K = 3.27 ± 0.1. On the basis of the substitution of zinc in its vincristine complex by calcium and magnesium ions respectively, the ratio of the corresponding stability constants could be estimated as KZn:KCa (and KZn:KMg) ∼ 105−3 × 104. The complex formation processes proved to be pH-independent in the pH range 3.4–5.5, indicating that the metal ions are coordinated by the unprotonated oxygen donor atoms of vincristine.

The acidic behaviour of osmium(VIII) and osmium(VI)

SummaryVarious methods yield a value of 6.3 · 10−13 for the apparent k1 and ∼ 4 · 10−15 for K2 of osmium(VIII) acid at 298 K. Spectrophotometric and potentiometric measurements yielded approximate values for the acidic constants of osmium(VI) acid: 3.2 · 10−9 and 4.0 · 10−11. The dependence of the pH of solution on the potassium osmate(VI) concentration can be interpreted in terms of the base inclusions in the preparation, rather than in terms of the dimerization of the osmium(VI).

Construction and characterization of a diode laser system for atomic spectrometric experiments

Construction and characterization of a simple but flexible, low cost diode laser system for atomic spectrometry is reported. Detailed electronic circuit layouts of the diode laser current controller, supplying maximum 1300 mA current with 1 mA resolution, and functional description of all other components (temperature controller, optics, mount, etc.) are given. The system features bi-directional computer control and full diode laser protection against voltage, current and temperature failure/overrun. Results of electronic and spectroscopic tests show that wavelength tuning with a precision of approximately 0.01 nm and current modulation frequency up to 10 kHz are possible with this system. Performance characteristics qualify the proposed instrumental setup for atomic fluorescence and absorption measurements in inductively coupled plasmas.

The OsO4-catalysed decomposition of hydrogen peroxide

The decomposition of H2O2 has been investigated in the presence of OsO4 as a catalyst. The rate of decomposition is proportional to the first power of the OsO4 concentration and to the power 1–1.2 of the hydrogen peroxide concentration. The pH dependence of the decomposition rate is quite characteristic; a high maximum is attained at pH 10.6 and a much lower one at about pH 8.3. With the aid of appropriate free-radical reagents and by e.s.r. spectrometry, it is shown that hydroxyl and superoxide radicals are formed during the catalysed decomposition. The rate of formation of the OH radical depends on the concentrations of H2O2 and OsO4, as well as on the pH. The rate of bleaching of N-dimethyl-p-nitrosoaniline and other dyes by the OH radical as a function of pH exhibits a maximum at pH 8.3. The OH radical is of both primary and secondary origin, and is involved in a chain reaction. The length of the chain is about 80–90 at pH 9 this value drops to ca. 10 and is independent of the pH. The apparent activation energy of the reaction route involving the OH radical is 105–111 kJ mol–1 at pH 10. Another decomposition route parallels that involving the OH radical, and predominates at pH > 9.5. In this case the catalysed decomposition can be approximated on the assumption that peroxo-osmate anion acts as a nucleophile towards the non-dissociated hydrogen peroxide molecule. The temperature dependence of this rate component gives an apparent activation energy of 60 kJ mol–1 at pH 10.