Anales CIDEPINT
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Examinando Anales CIDEPINT por Autor "Castells, R. C."
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Acceso Abierto Concurrent solution and adsorption of hydrocarbons in gas chromatographic columns packed with different loadings of 3- methylsydnone on chromosorb P(1998) Castells, R. C.; Romero, L. M.; Nardillo, A. M.Thermodynamic properties of solution in 3-methylsydnone (3MS) and of adsorption at the nitrogen/3MS interface were gas chromatographically measured for a graup of fifteen hydrocarbons at infinite dilution conditions. Retention voluntes were measured at five temperatures within the range 37-52°C in six columns containing different loadings of 3MS on Chromosorb P AW. Partition and adsorption coejficients were calculated and from their temperature dependence the corresponding enthalpies were obtained, although with considerable error; infinite dilution activity coejficients of the hydrocarbons in the bulk and in the surface phases demonstrated an strong correlation. Bulk activity coefficients in 3MS were very much smaller than those previously measured for the same solutes in formamide (FA) and in ethyleneglycol (EG), and were also smaller than what could be predicted on account of 3MS cohesive energy density as estimated from the quotient a/v13 (cr. surface tensión; v: molar volume). There was not such a large difference between the surface activity coefficients in the three solvents; furthermore, the quotients (surface activity coefficient/bulk activity coefficient) for a given solute in 3MS were twice as large as in FA and about three times larger than in EG. These results make evident the difficulties inherent in the prediction of surface phase properties from those in the bulk, and casi doubts on the pertinency of employing the surface tensión to compare cohesive energy densities of polar solvents with important Chemical dijferences. - Artículo
Acceso Abierto Influence of differences between sample and mobile phase viscosities on the shape of chromatographic elution profiles(1998) Castells, R. C.; Castells, Cecilia Beatriz; Castillo, M. A.The injection of samples whose viscosities are appreciably different from íhat of the motile phase can result in highly distorted elution profiles, showing severai maxima. The distortions are produced at the rear of the band when the viscosity of the sample solvent is higher than that of the motile phase. It is shown that the distortion of the peaks produced on injecting arbutin in columns of aminopropyl silica, using water as mobile phase and mixtures of 2-propanol and water as the sample solvent, grows in importance when the sample size increases, when the viscosity of the sample solvent increases and when the flow rate is decreased On the other side distortions at the band front are observed when arbutin dissolved in water or in acetonitrile + water mixtures is injected in a 2-propanol-water (50:50) mobile phase of higher viscosity. These trends are coincident with the predictions of a hydrodynamic instability criterion postulated several years ago and up to now almost entirely ignored in chromatography, except in relation with size exclusión chromatography. - Artículo
Acceso Abierto Thermodynamic consideration of the retention mechanism in a poly(perfluoroalkyl ether) gas chromatographic stationary phase used in packed columns(1996) Castells, R. C.; Romero, L. M.; Nardillo, A. M.Retention voluntes of fifteen hydrocarbons were measured in columns containing several concentrations of a commercial poly(perfluoroalkyl ether), Fomblin Y HVAC 140/13, as the stationary phase. Two different type ofpacking were studied: one ofthem employed pre-silylated Chromosorb P AW DMCS as the solid support, and the other type wasprepared by coating the stationary phase on Chromosorb P AW and silylating on-column. On-column silylated columns showed unequivocal symptoms of partial deactivation; retention volumes changed regularly with the contení of stationary phase in pre-silylated columns. Analysis of retention in pre-silylated columns indicates that a mixed mechanism (partition and adsorption on the gas-liquid interface) is operative. Systems hydrocarbon + perfluorocompound show pronounced positive deviations from the ideal behaviour that can be attributed to repulsión between the hydrocarbon and the perfluorocompund segments.