Irena Jančářová

Determination of trace lanthanides in their pure oxides by liquid chromatography-emission spectrometry

Traces of lanthanides can be separated effectively from major lanthanide oxides by liquid chromatography on a column of Separon SGX-C-18 silica gel modified by sorption of ammonium dodecylsulphate, and determined by flame - or inductively coupled plasma-atomic emission spectrometry. Spectral interferences from the major component at concentration ratios up to 10(4)-10(6) can be eliminated by isocratic or stepwise pH-gradient elution with ammonium 2-hydroxyisobutyrate. Methods of determining europium, ytterbium and holmium in yttrium, lanthanum and lutetium oxides are described. The flame method is shown to have some advantages.

Spectrophotometric study of time stability and acid-base characteristics of chelerythrine and dihydrochelerythrine

AbstractTime stability, acid-base and UV-VIS spectral properties of dihydrochelerythrine (DHCHE) were studied spectrophotometrically in water:methanol and water:ethanol media. DHCHE is stable in strongly acid milieu (pH < 3) and at the higher amounts (60% v/v) alcohol. Acid-base characteristics and UV-VIS spectral properties of chelerythrine (CHE) were studied in aqueous solutions in the presence of different concentrations of HCl, HNO3, H2SO4, H3PO4 and their mixtures. Remarkable shifts of formation parts of absorbance-pH (A-pH) curves to the alkaline medium were observed depending on the type and concentration of inert electrolyte (most remarkable for HNO3 and HCl). The corresponding equilibrium constants pKR+ of the transition reaction between charged iminium Q+ and uncharged QOH (pseudo-base, 6-hydroxy-dihydro derivative) forms of chelerythine were calculated using a numerical interpretation of A-pH curves by a SQUAD-G computer program which ranged from 8.51–9.31. The highest changes of ΔpKR+ (0.75 and 0.53) were observed for H3PO4 and H2SO4, respectively. The priority effect of ionic species and ionic strength was confirmed in the presence of additions of NaCl and KCl. The strength of interaction of CHE with biomacromolecular compounds (i.e., peptides, proteins, nucleic acids etc.) may be affected because of the observed influence of both cation and anion of the inert electrolyte on acid-base behavior.

Acid-base behaviour of sanguinarine and dihydrosanguinarine

Acid-base and optical properties of sanguinarine and dihydrosanguinarine were studied in the presence of HCl, HNO3, H2SO4, H3PO4, CAPSO and acetic acid (HAc) of different concentrations and their mixtures. The equilibrium constants pKR+ of the transition reaction between an iminium cation Q+ of sanguinarine and its uncharged QOH (pseudo-base, 6-hydroxy-dihydroderivative) form were calculated. A numerical interpretation of the A-pH curves by a SQUAD-G computer program was used. Remarkable shifts of formation parts of absorbance-pH (A-pH) curves to alkaline medium were observed. The shifts depend on the type and concentration of inert electrolyte (the most remarkable for HNO3 and HCl). The corresponding pKR+ values ranged from 7.21 to 8.16 in the same manner (ΔpKR+ = 0.81 and 0.73 for HNO3 and HCl, respectively). The priority effect of ionic species and ionic strength was confirmed in the presence of NaCl and KCl. The strength of interaction of SA with bioactive compounds (i.e. receptors, transport proteins, nucleic acids etc.) may be affected because of the observed influence of both cations and anions of the inert electrolytes.

Determination of uranium in technological waters by ion-pair liquid chromatography

U(VI) can be efficiently determined in the range 0.3-1OmM after its separation from Th(IV), Zr(IV), Al(III), Fe(III), lanthanides and other ions by ion-pair liquid chromatography on a 3 x 150 mm glass column packed with Separon SGX C18 modified with sorbed ammonium dodecyl sulphate. Traces of uranium can be preconcentrated directly on the analytical column from acidified water solutions and separated from Th, Zr, Al, Fe, lanthanides and other elements, with an enrichment factor of

Determination of traces of lanthanides in cerium oxide by liquid chromatography with on-column preconcentration

100 and recovery of 98 +/- 8%, by isocratic or pH or concentration gradient elution with ammonium 2-hydroxy-2-methylpropionate or ammonium citrate solution. Post-column derivatization with 25muM Arsenazo III in 0.1M formate buffer at pH 2.7 is used for detection and quantification.

Changes of organic acids and phenolic compounds contents in grapevine berries during their ripening

SummaryTraces of lanthanides can be effectively separated from other lanthanides in major concentrations and other elements by liquid chromatography on a column of Separon SGX C18 silica gel modified by sorption of ammonium dodecylsulphate or ammonium octanesulphonate and determined spectrophotometrically with Arsenazo III. Isocratic or stepwise acidity gradient elution with 90 mmol/l of ammonium 2-hydroxy-2-methylpropionate (HIBA) or 60 mmol/l of ammonium citrate was used. Interferences by the elements up to 103–104 concentration ratio can be eliminated. Lanthanides at mg/g level can be determined in cerium oxide with a relative standard deviation sr<2.5% (n=5).

Effect of tensides on the optical properties of sulfophthalein dyes

AbstractChanges of total content of phenolic substances, alteration in total titratable acidity and differences in tartaric acid content in grapes of four white (Müller-Thurgau — MT, Pinot Blanc — Rulandské bílé in Czech, RB, Sauvignon (Sg), and Muscat Ottonel — Muškát Ottonel in Czech, MO) and two blue (Dornfelder — Df and Blue Frankish — Frankovka in Czech, Fr) grapevine varieties throughout their growth, ripening and maturing (July–November). Potentiometric titration was applied for the determination of total titratable acids in grapes (expressed as tartaric acid equivalents in g L−1). A spectrophotometric method according Rebelein based on the formation of a colored complex of ammonium metavanadate and tartaric acid was used for determination of tartaric acid in green juice made by pressing unripe grapes. A spectrophotometric method based on reduction of phosphomolybdato-tungsten complex in alkaline solution using Folin-Ciocalteau reagent was applied for determination of total content of phenolic substances (TCP).