Jaroslav Zýka

CYCLODEXTRINS IN ANALYTICAL CHEMISTRY

Cyclodextrins play an important role in all major areas of modern instrumental analysis. Most of the interest in cyclodextrins results from their ability to form inclusion (host-guest) complexes with a variety of molecules and ions in aqueous solutions. Complexation by cyclodextrins can alter some of the physical and chemical properties of guest molecules, such as solubility, chemical reactivity and the spectroscopic and electrochemical properties, and many of these effects can be utilized in a variety of chemical analytical techniques. This review summarizes the use of cyclodextrins in major areas of analytical chemistry such as chromatography, electrophoresis, spectroscopy, electrochemistry and as analytical sensors.

Electrochemical oxidation of some aromatic amines in acetonitrile medium: II. Benzidine, N,N,N′,N′-tetramethylbenzidine, and 1,4-phenylenediamine derivatives

Abstract The polarographic behavior of benzidine, N,N,N′,N′-tetramethylbenzidine, 1,4-phenylenediamine, N,N,N′,N′-tetramethyl-1,4-phenylenediamine, N,N′-diphenyl-1,4-phenylenediamine, N,N′ — bis — 4 — dimethylaminophenyl — 1,4 — phenylenediamine, 4 — dimethylamino-N-methyldiphenylamine, 4-dimethylaminodiphenylamine and 4-aminodiphenylamine has been studied in acetonitrile medium on the rotating platinum electrode and the possibility has been shown of utilizing the oxidation wave of these substances for their polarographic determination, taking into account the influence of water in the solvent and the acidity of the medium. Coulometric generation at constant current has been used to investigate the number of electrons exchanged in the reaction. The products formed in the electrode reaction are discussed.

Electrochemical oxidation of some aromatic amines in acetonitrile medium. I. N,N-dimethylaniline, triphenylamine, diphenylamine and di-4-tolylamine

Abstract The polarographic behavior of N,N-dimethylaniline, triphenylamine, diphenylamine, and di-4-tolylamine has been studied in acetonitrile medium on a rotating platinum electrode. It has been found possible to apply the oxidation waves of these substances to their polarographic determination, considering the water content of the solvent, temperature and acidity of the medium. Constant current coulometric generation has been used to study the number of electrons exchanged in the reactions. The products formed in the electrode reaction are discussed.

The preparation and properties of the acetate complex of trivalent cobalt

Abstract A reasonably stable solution of the cobalt(III) acetate complex in glacial acetic acid, containing no water or cobalt(II), has been prepared by the anodic oxidation of the corresponding cobalt(II) acetate solutions at a platinum electrode in a closed system. Cobalt(III) acetate has also been electrolytically prepared without the addition of sodium acetate. Various materials have been tested as membranes because cellophane, which is usually used, has too high electric resistance and too low mechanical strength. The concentration of water in cobalt(III) acetate solutions has been determined by dielectric constant measurements and it has been found that the cobalt(III) acetate stability is almost independent of the water concentration within the range of 0 to 2% of water. In the closed system, the current efficiency was in the range of 60 to 70%; the best reproducibility was obtained using a porous glass membrane.

Oxidation study of sentisic acid and its derivatives and of α-tocopherol

Abstract Among all the redox titrants examined, iodine in almost neutral medium and Pb(IV) acetate in glacial acetic acid proved to be the best for volumetric determination of sodium gentisate. The results are satisfactory with respect to twoelectron oxidation of the substance and the methods can be applied for its quantitative determination. α-Tocopherol is quantitatively oxidized with Co(III) acetate in glacial acetic acid to the corresponding quinone. The reaction product which has been shown in Fig. 10, Reaction I. α-Tocopherol acetate can similarly be quantitatively estimated with Co(III) acetate in glacial acetic acid after its trans -esterification.

Oxidation of some inorganic systems by means of cobalt(III) acetate

Abstract A stable solution of Co(III) acetate was prepared and conditions were found for its use for the potentiometric volumetric determination of I- (in the presence of Br − and Cl − ), NO 2 − (in the presence of NO 3 − ), S 2 O 3 2− , peroxides , N 2 H 4 · H 2 SO 4 and NH 2 OH · HCl .

The study of the oxidation properties of cobalt(III): Part II. The oxidation of iodides and bromides

Abstract The oxidation of iodides and bromides by trivalent cobalt was studied by direct potentiometric titration with a solution of Co(ClO 4 ) 3 , and spectrophotometrically by kinetic measurements of the Co(III) reaction with bromides. The reaction proceeds according to the mechanism: The rate-determining step is reaction (1) which obeys the rate equation −d[Co(III)]/d t = k [Co(III)][Br − ] x [H + ], where x ≦ 1. For x = 1, k = 5 mol −2 l 2 s −1 .

Investigation of the formal redox potentials of the system Pb4+/Pb2+ with regard to the use of lead tetraacetate in volumetric analysis

Abstract The values of the formal redox potential of the system Pb4+/Pb2+have been measured in media of hydrochloric acid; perchloric acid and acetic acid (also with the addition of potassium acetate). The dependence of the formal redbx potential value on the concentration of the acids mentioned, on the concentrations of the Pb4+ and Pb2+ ions in the solution, and on time, has been investigated.

The study of the oxidation properties of cobalt(III): Part I. The reaction of cobalt(III) with hydroxylamine

Abstract The kinetics of the Co(III) reaction with NH 2 OH in various media was studied spectrophotometrically with regard to the possible analytical use of Co(III). The results of measurements in media of 3–8 M HClO 4 and 0.1–1 M HSO − 4 in 3 M HClO 4 can be summarized as follows: 1. The reaction was found to be first order with respect to Co(III) and of zero order with respect of NH 2 OH. 2. The reaction velocity increases linearly with increasing concentrations both of HClO 4 and of HSO − 4 3. The reaction velocity also increases linearly with increasing Co(II) concentration and it is possible to achieve a higher reaction rate in this way than by the addition of HSO − 4 . 4. This behaviour can be explained either by assuming hydrogen bonding between Co 3+ aq and Co 2+ aq which makes the electron transfer easier in some systems, or by formation of a more reactive complex between Co(III) and Co(II) than the simple Co(III) ion.

Titration of sulphydryl substances by lead tetraacetate

Abstract Mercaptans may be titrated by standard lead tetraacetate solutions in glacial acetic acid media., using potentiometric or visual control with quinalizarin as indicator, the appropriate disulphide being formed. The method is well suited for routine analysis. Using thiglycollic acid, cysteine, thiourea and thiosemicarbazide as model substances, it has been found that -SH substances can be oxidised to various oxidation states according to the medium employed (e.g. dilute acetic acid, possibly containing mineral acids). These reactions were investigated using an excess of the reagent. The excess was determined by back titration with standard hydroquinone solution.