Chemistry December 2002 Vol 51/4 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Chemistry



Volume 51 No. 4December 2002



Automaticon-line sample introduction for capillary electrophoresis connected viaelectrospray with condensation nucleation light scattering detection;187–199

Arkadi Ebber and Mihkel Kaljurand

Abstract. Condensation nucleation light scattering detection (CNLSD) isconsidered to be a sensitive and universal detection method for capillaryelectrophoresis (CE). It may be connected to the separation capillary viaelectrospray (ES). Conventional sample introduction in a CE–ES–CNLSD systemrequires interruption of the electroosmotic flow (EOF) and ES by switching offthe CE and ES high voltages.

Wedeveloped for CE–ES–CNLSD an automatic sample injection system, working inon-line mode, which can perform multiple sample introductions at the highvoltage electrode without corrupting EOF and ES. The main part of the injectionsystem is a pneumatically actuated sampler with a narrow-bore channel servingas an inlet reservoir for CE. In the channel the flow pulses of buffer andsample solutions can rapidly replace each other without bubbling orinterrupting the electric current through the capillary. The injection device istotally computer controlled and it can perform hundreds of sample introductionsaccording to any prescribed sequence with once established stable ES. Thereproducibility of the set-up performance, measured from the peak areas, was95–96%.

Key words: capillary electrophoresis, automatic injection, CNLSD.

Theoreticalbasis for the estimation of nitrite as a 4-nitroso-2,5-dimethylresorcinolatecomplex; 200–214

Ille Johannes and LaineTiikma

Abstract. A theoretical basis is presented for testing nitrite as cobaltand iron(II) 4-nitroso-2,5-dimethylresorcinolates. The joint effect of pH andconcentration of the reagents on the absorbance is described by algorithmsconsidering the stability of the complex formed, solubility product of theinsoluble salt formed, and acidic dissociation of the iron and cobalt complexesand 4-nitroso-2,5-dimethylresorcinol. Acidic dissociation constants, molarabsorptivities, stability constants, and solubility products of the species areestimated. The pH-dependences of the partial contributions to the totalabsorbance of the five coloured species formed are described.

Key words: nitrite, alkylresorcinols, analysis.

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

Helle Kirss, Mati Kuus, Enn Siimer, and LudmillaKudryavtseva

Abstract. Isobaricvapour–liquid equilibrium (VLE) was measured for the systemtoluene + p-xylene + 1,2-dichloroethaneand for constituent binaries at pressures 26.66, 53.33, 79.99, and101.32 kPa. A modified Wilson equation with a linear temperaturedependence of the main parameters  was used to correlatethe binary VLE data and to predict those of the ternary system. Excessfunctions of the ternary system at 298.15 K were compared.

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

Compositionof blackcurrant aroma isolated from leaves, buds, and berries of Ribesnigrum L.; 225–234

Anne Orav, Tiiu Kailas, and Mati Müürisepp

Abstract. Volatile aroma compounds of simultaneous distillation andextraction (SDE) from black­currant (Ribesnigrum L.) leaves, buds, and berries were analysed by capillary gaschromato­graphy with OV-101, PEG 20M, and CYDEX B stationary phases,and by gas chromatography–mass spectrometry. A total of 63 compounds wereidentified. The monoterpenes 3-carene (20–27%), (Z)-b -ocimene (2–11%), b -phellandrene (3–11%), and terpinolene (7–10%) and thesesquiterpenoids (E)-b -caryophyllene (5–9%) and caryophyllene oxide (0.5–10%) wereidentified in high quantities in blackcurrant oils. The oil yields fromblackcurrant 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 ripeningprocess was studied and the enantiomeric ratio of some monoterpenoids wasdetermined.

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

Ultrasonicacceleration of ester hydrolysis in ethanol–water and 1,4-dioxane–water binarysolvents; 235–239

Hannes Hagu, Siim Salmar, and Ants Tuulmets

Abstract. Kinetics of theacid-catalysed hydrolysis of butyl acetate in ethanol–water and1,4-dioxane–water binary solutions was investigated without sonication andunder ultrasound at 22 kHz. Rate enhancements by 2.42 times or less werefound to decrease with an increase in the content of the hydrophobic co-solventin the binary solvent. The results suggest that ultrasonic acceleration of thereaction may be interrelated to the perturbation of hydrophobic solute–solventinteractions.

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



Contentsof volume 51; 240