Ferenc F. Gaál

Photocatalytic degradation of the insecticide acetamiprid on TiO2 catalyst

The work is concerned with the photocatalytic degradation of acetamiprid, a widely used pyridine-based neonicotinoid insecticide, in UV-irradiated aqueous suspensions of O2/TiO2. The rate of degradation was studied by HPLC/DAD and UV spectrophotometry. It was found that the reaction in the investigated concentration range (0.5-2.0 mg cm-3) is of a pseudo-first order. The 1H NMR analysis indicated that beside acetaldehyde, formic and acetic acid, pyridine-containing intermediates (e.g. 6-chloronicotinic acid) formed during the process. The HPLC/MS measurements also proved the presence of aromatic degradation intermediates. During the photocatalytic process the pH changed by even three units, from 5 to 2. In contrast to the photocatalytic results in the photolytic experimental conditions, acetamiprid appeared to be stable. To get a deeper insight into the complex photocatalytic process of acetamiprid, the photocatalytic degradation of 6-chloronicotinic acid, the detected pyridine-based degradation product, was also investigated.

Determination of organic bases in non-aqueous solvents by catalytic thermometric titration

Catalytic thermometric titrations have been developed for bases (brucine, diethylaniline, potassium acetate and triethylamine) in acetic acid by continuous and discontinuous addition of the standard solution and automatic temperature recording. The determination of weak bases, e.g., antipyrine, unsuccessful in acetic acid by catalytic thermometric titration, has been achieved by using nitromethane or acetic anhydride as solvent. Catalytic thermometric titrations were also performed by coulometric generation of hydrogen ions for the determination of micro amounts of weak bases in a mixture of acetic anhyride and acetic acid.

Catalytic amperometric and catalytic constant-current potentiometric titrations of silver(I), palladium(II) and mercury(II)

Amperometry and constant-current potentiometry were used to follow the course of catalytic titrations of silver(I), palladium(II), and mercury(II) with potassium iodide. The Ce(IV)As(III) and Ce(IV)Sb(III) systems in the presence of sulphuric acid were used as indicator reactions. The possibilities of application of platinum, palladium, gold, graphite, and glassy-carbon indicator electrodes were investigated. Graphite appeared to be somewhat more advantageous than the other electrode materials. The effect of concentration of the components of the indicator reactions, the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 30-3000 mug of silver(I) nitrate, 90-900 mug of palladium(II) chloride, 130-1300 mug of mercury(II) chloride, and 150-1500 mug of mercury(II) nitrate were determined with a relative standard deviation less than 1.0%. The results obtained were in good agreement with those of comparable methods. The catalytic titration method developed was applied to determination of mercury in Unguentum Hydrargyri.

A Thermoanalytical Study of the Solid State Reactions in the K2CO3-MxOy Systems. Evidence for a kinetic compensation effect

This paper presents the results obtained in the investigation of the reactions of potassium carbonate with some transition metals oxides (TiO2 , V2 O5 , Cr2 O3 , MnO2 , Fe2 O3 ). The reactions were carried out under non-isothermal conditions, and thermogravimetric analysis was used to monitor the transformation degree a. Experimental data indicated that the reaction of potassium carbonate and iron(III) oxide occurs in one stage, whereas the reactions of the oxides of titanium, vanadium, chromium and manganese are more complex, involving two-stage processes. Activation energies and pre-exponential factors were determined for all the processes taking place in the investigated systems. For the second stage of the reaction of K2 CO3 with Cr2 O3 , and V2 O5 the obtained values of activation energy were 59.2 and 512 kJ mol−1 respectively. Based on the values of activation energy and pre-exponential factor, the existence of a kinetic compensation effect was postulated for the three homologous series of reactions.

Microcomputer-aided titrimetric determination of bromine-containing active ingredients in some drug formulations

Several microcomputer-aided titrimetric procedures were developed to determine active components with bromide or covalently bound bromine in their molecules in some pharmaceutical preparations of different formulations. Titrations were carried out either with a standard silver nitrate solution (indirect determination), employing catalytic spectrophotometric, potentiometric and controlled-current potentiometric methods to monitor the course of the titration, or with a standard solution of perchloric acid in acetic acid (direct determination) in catalytic thermometric titration. The indicator reaction used in catalytic spectrophotometric titrations was the peroxodisulfate—sulfanilic acid reaction in the presence of 2,2′-bipyridine as activator and acetate buffer (pH 4.35), whereas in catalytic thermometry it was the hydroquinone—acetic anhydride reaction. In the controlled-current potentiometric procedure, use was made of the peroxodisulfate decomposition reaction in the presence of 2,2′-bipyridine as the indicator. Amounts of 10–20 µmol of the investigated active ingredients per titration were determined with a relative standard deviation that, depending on the procedure and mode of sample preparation, was in the range 0–2.6%. The results are comparable to those obtained by official methods. The microcomputer-aided titrimetric procedures developed are relatively fast and economical and can be applied to the analysis of large numbers of pharmaceutical products.

Application of an indicating system of bismuth electrodes for the determination of organic bases and acids in nonaqueous solutions

ZusammenfassungTertiäre Amine und Salze organischer Säuren werden durch Titration mit einer Lösung von Perchlorsäure quantitativ bestimmt. Das verwendete Indicatorsystem besteht aus einem Paar polarisierter oder nichtpolarisierter Wismutelektroden. Das gleiche System wurde auch angewandt auf die titrimetrische Bestimmung von Mono- und Polycarbonsäuren mit einer starken Base. Die Ergebnisse stimmen gut mit denen der potentiometrischen bzw. katalytisch-thermometrischen Methode überein.SummaryTertiary amines and salts of organic acids have been titrated by means of perchloric acid applying a biamperometric indicating system consisting of a polarised or unpolarised pair of bismuth electrodes. Also, mono- and polycarboxylic acids, alone and in mixtures, have been determined with a strong base using the same end-point detection technique. The results obtained are in good agreement with those of potentiometry or catalytic thermometry.

Contributions to the theory of catalytic titrations. I: Complexometric catalytic titrations

Complexometric catalytic titrations with both volumetric and coulometric addition of the titrant have been simulated. By taking into consideration the equilibrium concentration of the catalyst during the titration, general mathematical equations have been set up. The influence of several factors on the shape of the simulated catalytic titration curve has been investigated and is discussed. The work also deals with the conditions under which the approximate mathematical expressions (equilibrium concentration of the catalyst being neglected) can be applied to simulate the catalytic titration curves with a satisfactory accuracy.

Determination of fluoride with thorium nitrate by catalytic titration

Amperometry, constant-current potentiometry and spectrophotometry were used to follow the course of catalytic titrations of fluoride and silicofluoride with thorium nitrate. The hydrogen peroxide-iodide system was used as the indicator reaction. Titrations were performed in 50% ethanolic acetate buffer, pH 3.6. Amounts of 3.70-6.85 mg of ammonium fluoride, 5.53-10.79 mg of potassium fluoride and 4.34-8.41 mg of sodium silicofluoride were determined with a maximum average deviation of 0.9%. The results obtained are in good agreement with those of comparable methods.

Determination of EDTA by catalytic amperometric and catalytic potentiometric titration at a small constant current

ZusammenfassungDie amperometrische und die potentiometrische Methode bei kleinem konstantem Strom wurden für die Verfolgung katalytischer Titrationen ausgearbeitet. ÄDTA wurde in Ammoniakmedium mit 0,1 M Kupfer(II)-chlorid in Anwesenheit von Wasserstoffperoxid als Indicator titriert. Mengen von 42,26–126,87 mg ÄDTA wurden mit einer mittleren Abweichung von 0,55% bestimmt. Die Ergebnisse stimmen gut mit denen vergleichbarer Methoden überein.SummaryAmperometric and potentiometric methods at a small constant current were developed to follow the course of catalytic titrations. In ammoniacal medium EDTA was determined by titration with 0.1 M copper(II) chloride in the presence of hydrogen peroxide as the indicator. Amounts of 42.26–126.87 mg of EDTA were determined with a maximal average deviation of 0.55 %. The results obtained are in good agreement with those of comparable methods.

Titrimetric determination of fluoride in some pharmaceutical products used for fluoridation

Two titrimetric methods were developed for the determination of fluoride contents in some pharmaceutical preparations used for fluoridation. One of the methods is catalytic controlled-current potentiometry involving two identical platinum indicator electrodes and thorium nitrate as titrant. The reaction between hydrogen peroxide and potassium iodide in the presence of acetate buffer (pH 3.6), which is catalysed by the excess of thorium nitrate, served for the end-point indication. The other method is the automatic potentiometric titration involving a fluoride-selective electrode and lanthanum nitrate as titrating agent. In both procedures, special attention was paid to sample pretreatment and to determination of optimal experimental conditions. Fluoride contents in the range 16-32 microg/ml are determined with a relative standard deviation less than 1.34%. The results are compared to those obtained by standard methods described in the United States Pharmacopeia XXI and recommended by the manufacturer of the preparations.