E.sz. Kováts

A tailor-made C87 hydrocarbon as a possible non-polar standard stationary phase for gas chromatography

Abstract A hydrocarbon of empirical formula C87H176 has been found to have advantageous properties for use as a stationary phase in gas chromatography. It is a non-polar solvent with a working temperature range from 30°C to about 280°C. Being a pure substance, it has reproducible properties. The information necessary for determining the precise position of the starting point of the chromatogram is given, and its separation properties are discussed, taking as examples the chromatographic behaviour of n-alkanes and other selected compounds. With the aid of these data, this hydrocarbon is compared with squalane and the methylsilicones, and proved to show most of the advantages of both of these phases.

Composition of essential oils : Part 7. Bulgarian oil of rose (Rosa Damascena mill.)☆

Abstract A first-quality Bulgarian oil of rose was analysed. After classical group separation, the neutral part was further subdivided by “group displacement chromatography” on deactivated silica gel into non-polar, slightly polar and polar parts. Acids and phenols were analysed as methoxy and ethoxy derivatives. The individual groups were first distilled. Pure components were isolated from the distillation fractions by preparative gas chromatography. Fractions isolated on a hydrocarbon-type stationary phase (Apiezon L) were further separated on a poly(ethylene glycol) (Emulphor-O) to give the pure components. In a second analysis, the oil was separated in a continuous counter-current separator with 680 cells in order to isolate the fraction containing those compounds which are responsible for the “honey note” of the oil. The enriched part ( ca . 1% of the oil) was then separated as described above. As a result, 127 compounds were isolated and identified, representing 98.6% of the volatile part. Of these only 40 had previously been reported. The compound mainly responsible for the sweet odor (“honey note”) was shown to be a dehydroisoionone comprising 0.1% of the oil. Because of its organoleptic importance, damascenone is proposed as common name for this substance.

Chemically modified silicon dioxide surfaces Reaction of n-alkyldimethylsilanols and n-oxaalkyldimethylsilanols with the hydrated surface of silicon dioxide — the question of the limiting surface concentration

Abstract Firstly, a model is proposed for the surface of highly dispersed silicon dioxides (Aerosil, Cabosil). In the first part, the investigation of the uncatalysed reaction of the surface hydroxyls on Cabosil with alkyl and oxa-alkyldimethylsilanols is described. The reaction mechanism is discussed on the basis of kinetic measurements. The reaction attains a limiting surface concentration of 3.1 μmol m−2 of alkyldimethylsiloxy groups, a value which is independent of the chain length of the non-branched alkyl substituent, as well as of the reaction temperature between 200 and 340°C. By repeating the reaction, the surface concentration can be further increased. However, the limiting value attained after about three repeated treatments at 300°C depends on the chain length of the alkyl substituent, 4.0 μmol m−2 for trimethylsiloxy groups and 3.5 for the other alkyldimethylsiloxy groups with longer alkyl or oxa-alkyl substituents. An interpretation of the results is proposed in the light of the suggested model. In the second part, the investigation of the catalysed reaction is described. The reaction is catalysed by bases, the best catalyst having protons attached to the basic center. By repeating the reaction, a layer could be chemically bonded onto the surface, the density of which is determined only by the size of the substituent. The maximum attainable concentration depends also on the temperature. Such a dense layer could not be prepared with oxa-alkyldimethylsiloxy substituents.

Study of the adsorption effects at the surface of poly-(ethylene glycol)-coated column packings

Abstract Gas chromatographic data for a series of solutes on a purified dimethoxypoly-(ethylene glycol) are presented. The retention volumes were measured on columns prepared with two supports, one wettable and the other partially wettable by the stationary phase, at four temperatures and on four column packings with different loadings. The data permitted the evaluation of equilibrium parameters characterizing solute absorption in the stationary phase and solute adsorption at the different interfaces in the column. An attempt to interpret the results is described.

Characterization of low energy surfaces by a standard surface method

Abstract An empirical method is presented for the prediction of contact angles an rough, swollen and smooth low energy surfaces. It consists of comparing free energies of adhesion on a given surface with those measured an standards. It is shown that the dispersion part of the free energy of adhesion is proportional to that measured on a non-polar standard surface and the permanent polar part to that on a polar standard. By the method proposed the surface roughness and its swelling capacity can also be deduced from wetting data. The method was applied first to surfaces prepared for this project. A first series of glass surfaces were covered by some organic substituents such as methyl, phenyl and adamantyl. A second series of surfaces were synthesized exposing long alkyl chains, which can be swollen by wetting agents. The method is also applied for the evaluation of some literature data. Wetting agents having molecules similar in shape to non-branched alkanes can form a mixed crystal layer with alkyl chains anchored at the surface. The crystalline layer shows anomalous wetting which was studied in some detail.

The absolute configuration of thujane

Abstract (+)- cis - and (+)- trans -Thujane (XIV and XV) have been correlated with (+)-pulegone (IX) via (+)-pulegene (XIII). Using stereospecific reactions, the hydrocarbons of the thujane series have been linked with their oxygenated members. The absolute configurations found by Norin for these substances are in accord with our findings.

Pair-wise interactions by gas chromatography. VI: Interaction free enthalpies of solutes with primary methoxyalkane, cyanoalkane and alkanethiol groups

Three polar-type liquids, P, having methoxy, cyano or thiol substituents in primary positions on a branched paraffin skeleton were used as stationary phases. The molecules of these stationary liquids have the same form and nearly the same size as that of the non-polar parent branched paraffin, C78H158 (C78). Gas chromatographic retention data of some 150 molecular probes were measured on pure P-type liquids and on P/C78 mixtures with a volume fraction fP of 0.50. Based on these data interaction free enthalpies could be calculated between a probe and the polar substituent, both at infinite dilution in the alkane solvent.

Pair-wise interactions by gas chromatography. IV: Interaction free enthalpies of solutes with trifluoromethyl-substituted alkanes

Abstract Two polar-type liquids were used as stationary phases, one being a mono(trifluoromethyl) (MTF) and the other a tetrakis(trifluoromethyl) (TTF) derivative of the parent branched alkane, C 78 H 158 (C78). Gas chromatographic data for about 160 molecular probes were measured on pure MTF and on C78-TTF mixtures at several temperatures. It was found that data on MTF are the same as data on a C78-TTF mixture with ϕ TTF = 0.25, both melts having the same molar concentration of trifluoromethyl groups. Interaction free enthalpies were calculated from data measured on C78-TTF mixtures between the probe and a trifluoromethyl group, both at infinite dilution.

A study of column performances in gas chromatography : A C87 hydrocarbon on chemically modified supports

Abstract The surface of quartz plates and Chromosorb W were made to react with trimethylsilanol, docosyl-1-dimethylsilanol and 4,7-dioxaoctyl-1-dimethylsilanol. The density of the chemically bonded monomolecular layer is assumed to be maximal. One sample of Chromosorb W and one quartz plate were treated only by heating to 1250°. The modified support materials were used to prepare chromatographic columns with a C87 hydrocarbon stationary phase. Van Deemter plots of three substances were measured at each of the temperatures 60, 150 and 240°. The mass transfer terms of the calculated Van Deemter equations could be qualitatively related to wetting angles of the stationary phase, which were measured on the surface-modified vitreous quartz plates. The results indicate a method by which the column performances for the stationary phase used can be improved by suitable surface modification.

Pair-wise interactions by gas chromatography V. Interaction free enthalpies of solutes with primary chloro-and and bromoalkanes☆

Abstract Gas chromatographic data of ca. 140 molecular probes were measured on primary chloro and bromo derivatives of a C 78 branched alkane (C 78 H 158 ) as stationary phases. Interaction free enthalpies between solutes and the dipolar chloroalkyl and bromoalkyl groups were nearly the same. Slight differences may be explained by the higher polarizability of the bromo substituent.