CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Chemistry

Volume 51 No. 4 December 2002

Automatic on-line sample introduction for capillary electrophoresis connected via electrospray with condensation nucleation light scattering detection; 187–199

Arkadi Ebber and Mihkel Kaljurand

Abstract. Condensation nucleation light scattering detection (CNLSD) is considered to be a sensitive and universal detection method for capillary electrophoresis (CE). It may be connected to the separation capillary via electrospray (ES). Conventional sample introduction in a CE–ES–CNLSD system requires interruption of the electroosmotic flow (EOF) and ES by switching off the CE and ES high voltages.

    We developed for CE–ES–CNLSD an automatic sample injection system, working in on-line mode, which can perform multiple sample introductions at the high voltage electrode without corrupting EOF and ES. The main part of the injection system is a pneumatically actuated sampler with a narrow-bore channel serving as an inlet reservoir for CE. In the channel the flow pulses of buffer and sample solutions can rapidly replace each other without bubbling or interrupting the electric current through the capillary. The injection device is totally computer controlled and it can perform hundreds of sample introductions according to any prescribed sequence with once established stable ES. The reproducibility of the set-up performance, measured from the peak areas, was 95–96%.

Key words: capillary electrophoresis, automatic injection, CNLSD.

Theoretical basis for the estimation of nitrite as a 4-nitroso-2,5-dimethylresorcinolate complex; 200–214

Ille Johannes and Laine Tiikma

Abstract. A theoretical basis is presented for testing nitrite as cobalt and iron(II) 4-nitroso-2,5-dimethylresorcinolates. The joint effect of pH and concentration of the reagents on the absorbance is described by algorithms considering the stability of the complex formed, solubility product of the insoluble salt formed, and acidic dissociation of the iron and cobalt complexes and 4-nitroso-2,5-dimethylresorcinol. Acidic dissociation constants, molar absorptivities, stability constants, and solubility products of the species are estimated. The pH-dependences of the partial contributions to the total absorbance of the five coloured species formed are described.

Key words: nitrite, alkylresorcinols, analysis.

Isobaric vapour–liquid equilibria of the ternary system toluene + p-xylene + 1,2- dichloroethane; 215–224

Helle Kirss, Mati Kuus, Enn Siimer, and Ludmilla Kudryavtseva

Abstract. Isobaric vapour–liquid equilibrium (VLE) was measured for the system toluene + p-xylene + 1,2-dichloroethane and for constituent binaries at pressures 26.66, 53.33, 79.99, and 101.32 kPa. A modified Wilson equation with a linear temperature dependence of the main parameters was used to correlate the binary VLE data and to predict those of the ternary system. Excess functions of the ternary system at 298.15 K were compared.

Key words: vapour–liquid equilibrium, ternary system, toluene, p-xylene, 1,2-dichloroethane.

Composition of blackcurrant aroma isolated from leaves, buds, and berries of Ribes nigrum L.; 225–234

Anne Orav, Tiiu Kailas, and Mati Müürisepp

Abstract. Volatile aroma compounds of simultaneous distillation and extraction (SDE) from blackcurrant (Ribes nigrum L.) leaves, buds, and berries were analysed by capillary gas chromatography with OV-101, PEG 20M, and CYDEX B stationary phases, and by gas chromatography–mass spectrometry. A total of 63 compounds were identified. The monoterpenes 3-carene (20–27%), (Z)-b -ocimene (2–11%), b -phellandrene (3–11%), and terpinolene (7–10%) and the sesquiterpenoids (E)-b -caryophyllene (5–9%) and caryophyllene oxide (0.5–10%) were identified in high quantities in blackcurrant oils. The oil yields from blackcurrant buds were 0.21%, from leaves 0.04%, and from berries up to 0.003%. Variation in the concentrations of the oil components during the ripening process was studied and the enantiomeric ratio of some monoterpenoids was determined.

Key words: Ribes nigrum L., Saxifragaceae, blackcurrant, volatile aroma extract, enantiomeric ratio, GC/FID, GC/MS.

Ultrasonic acceleration of ester hydrolysis in ethanol–water and 1,4-dioxane–water binary solvents; 235–239

Hannes Hagu, Siim Salmar, and Ants Tuulmets

Abstract. Kinetics of the acid-catalysed hydrolysis of butyl acetate in ethanol–water and 1,4-dioxane–water binary solutions was investigated without sonication and under ultrasound at 22 kHz. Rate enhancements by 2.42 times or less were found to decrease with an increase in the content of the hydrophobic co-solvent in the binary solvent. The results suggest that ultrasonic acceleration of the reaction may be interrelated to the perturbation of hydrophobic solute–solvent interactions.

Key words: binary solvent mixtures, ester hydrolysis, ultrasound.

Contents of volume 51; 240