Multilayer adsorption of alcohols from benzene/n-heptane mixtures on silica gel

An equation for multilayer adsorption from multicomponent liquid mixtures on solid surfaces¹ has been examined. For this purpose experimental adsorption data for four alcohols from benzene/n-heptane mixture on silica gel have been measured. Average number of the adsorbed layers, heterogeneity parameter and capacity of the surface phase have been evaluated by using the equation mentioned above.

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Mehrschichten-Adsorption von Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel

Zusammenfassung Eine Gleichung für Mehrschichten-Adsorption an festen Oberflächen¹ aus Mehrkomponentenlösungen wurde getestet. Zu diesem Zweck wurden experimentelle Daten für die Adsorption von vier Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel herangezogen. Der Mittelwert für die Anzahl der Adsorptionsschichten, der Heterogenitätsparameter und die Kapazität der Oberflächenphase wurde aus dieser Gleichung berechnet.

     

Adsorption from binary solvent mixtures onto silica gel by HPLC frontal analysis

Summary The chromatographic technique of frontal analysis is applied to measuring adsorption from binary liquid mixtures by silica gel. The complete adsorption isotherm of a solvent mixture is obtained by measuring the break-through curves for a series of small concentration steps of the mobile phase. This method offers a direct way to determine the composition of the stationary phase in liquid-solid chromatography with mixed mobile phases. The surface excess isotherms of all binary systems formed by benzene, cyclohexane, and 1,2-dichloroethane, at the solution-silica gel interface at 25 °C are presented. The data of the three systems are shown to be thermodynamically mutually consistent.     

Study of adsorption from solutions by frontal chromatography

Summary The automatic frontal chromatography installation was described. By this chromatographic method the adsorption isotherm of benzene from n-heptane solutions on hydroxylated surface of silica with various porosity has been determined. This investigation was performed at different flow rates of eluent and in a wide range of concentrations. The isotherm of adsorption obtained by this chromatographic method has been compared with the results of the static measurements. The coincidence of adsorption isotherms measured at the various flow rates are shown to be a criterion of proximity the chromatographic process to the equilibrium.     

Adsorption from solutions of nonelectrolytes on heterogeneous solid surfaces: A four-parameter equation for the excess adsorption isotherm

A four-parameter single-solute adsorption isotherm equation is generalized to the adsorption of binary liquid mixtures of nonelectrolytes. This equation comprises all isotherms being a simple extension of theEverett isotherm to liquid adsorption on heterogeneous solid surfaces. The benzene—cyclohexane excess adsorption data on silica gel are studied by using this new equation.

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Adsorption aus Lösungen von Nichtelektrolyten an heterogenen festen Oberflächen: Eine Vierparametergleichung für die Excess-Adsorptions-Isotherme

Zusammenfassung Es wird eine Vierparameter-Isothermengleichung für binäre Lösungen von Nichtelektrolyten diskutiert. Diese Gleichung umfaßt alle Isothermen vom Typ der einfachen Erweiterung derEverett-Isotherme für Flüssig-Adsorption auf heterogenen festen Oberflächen. Die Daten für die Adsorption von Benzol—Cyclohexan werden mittels dieser neuen Gleichung behandelt.

     

Separation of urea and other polar compounds by HPLC

Summary Urea, glycolic and aminoxyacetic acid amides are the polar metabolites of 2-acetyl-3-phenyl-tetrahydro-1,2,4-oxadiazin-5-one (RGH 4615). They cannot be separated on octadecyl-, cyanosilyl- or amino-phase columns, but silica, used with C₃-C₄ alcohol and water mixtures as the eluent permits their separation. Besides refractive index detection and on-line radioactivity measurement the metabolic formation of¹⁴C-urea was proved by enzymatic cleavage into¹⁴CO₂.     

A gas chromatographic study of the adsorption of organics on thermally treated silicas

Summary Adsorption properties of thermally treated silica beads were investigated by the gas-solid chromatography method. Retention volumes of n-hexane, cyclohexane, benzene and carbon tetrachloride were measured on silica beads obtained from colloidal silica thermally pre-treated at 423–1 223 K. It has been found that the applied temperature does not change the crystal structure of the solids. The specific surface areas of the thermally treated samples remain practically constant up to 1073 K, and then sharply decrease toward 1 373 K. The partition coefficients for all adsorbates plotted against thermal treatment temperature exhibit a maxima laying between 773 and 1 073 K. Possible interactions between the organics and the surface are discussed in the light of determined thermodynamic quantities of adsorption. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Liquid chromatography of polymer mixtures by a combination of exclusion and full adsorption mechanisms. Three- and four-component polymer blends

Summary Coupling of full adsorption-desorption and size-exclusion chromatography (FAD-SEC) has been applied to the separation and molecular characterization of three- and four-component polymer blends. The method is based on the full adsorption of alln orn−1 components of the polymer blend in a specially designed FAD minicolumn. By appropriate eluent switching the adsorbed polymers are desorbed stepwise from the FAD minicolumn into an on-line SEC column for molecular characterization. It is shown that the desorption isotherms of particular blend components give valuable information about the appropriate displacer composition. The exact position of the desorption isotherms depends, however, both on the amount of polymer adsorbed and in the presence of other, chemically different, polymers within FAD column. The nature and composition of the displacer must, therfore, be adjusted if the intervals between the desorption of particular blend components are to be large enough to prevent displacement overlap. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

Theoretical studies on the adsorption from non-ideal binary liquid mixtures on heterogeneous surfaces involving difference in molecular sizes of components

An equation for the phenomenon of competetive adsorption from binary liquid mixtures onto solids has been derived using the kinetic approach. In this equation the difference of the molecular sizes, the non-ideality of both bulk surface phases, and the energetic heterogeneity of the solid surface have been taken into account.

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Theoretische Untersuchungen zur Adsorption aus nichtidealen binären Lösungsmittelgemischen an heterogene Oberflächen fester Körper unter Berücksichtigung der Unterschiede in den molekularen Größen der Komponenten

Zusammenfassung Auf Grund kinetischer Erwägungen wurde eine Gleichung, die die Konkurrenzadsorption aus binären Lösungsmittelgemischen an den Oberflächen fester Körper beschreibt, aufgestellt. In der Gleichung wurde der Größenunterschied der Teilchen, die Nichtidealität der Lösung in der Volumen- und Oberflächenphase, sowie die energetische Heterogenität der Oberfläche des festen Körpers berücksichtigt.

     

Physico-chemical applications of liquid chromatography I. Investigation of the adsorption of cardiac glycosides from water-ethanol solutions on silanized silica

Summary Using the cardiac glycoside cymarin as the example the application of liquid chromatography for the study of adsorption from solutions and the determination of the corresponding thermodynamic characteristics was investigated. The adsorption isotherm of cymarin at small concentrations from a water-ethanol solvent on silica gel modified by dimethyldichlorosilane was measured under static conditions using analytical LC to determine the concentrations of solutions after adsorption. The values of the Henry constants were obtained by extrapolating the slope of the adsorption isotherm down to zero concentration. The specific retention volumes for different but small sample sizes of cymarin in the chromatographic column were measured, the adsorbent and the water-ethanol eluent being the same as in the static conditions. The specific retention volume for a small (zero) sample size determined by liquid chromatography experiment coincides with the Henry constant of cymarin adsorption determined in static conditions. In favourable cases liquid chromatography can be used to determine the equilibrium constants for adsorption from solution. The dependence of the Henry constants on temperature was investigated for several cardiac glycosides. The influence of the modification of the adsorbent surface on the separation of the cardiac glycosides was also studied.     

Determination of urinary organic acids by HPLC

Summary A high-performance liquid chromatographic method for the simultaneous determination of urinary organic acids and creatinine for following the metabolism of aromatic solvents is reported. After extraction of acidified, filtered urine with diethylether followed by evaporation, the dried residue is dissolved in mobile phase. Hydroxybenzoic acid is used as internal standard. A column of Nucleosil C₁₈ is used with a precolumn of the same material. The mobile phase is acetonitrilephosphate buffer, pH 3.3 (1783). For determination of creatinine the sample is simply diluted 10-fold and the eluate monitored at 215 nm (UV). This technique gives highly reproducible results and is simple, reliable and useful for biological monitoring.     

Adsorption of Linear Polyethylene and Isotactic Polypropylene from 1,1,2,2-Tetrachloroethane and 1,2,3-Trichloropropane on to Polar Adsorbents

Linear polyethylene and isotactic polypropylene samples were dissolved in 1,1,2,2-tetrachloroethane or 1,2,3-trichloropropane and injected at 135 °C into columns packed with porous particles of hydroxyapatite, aluminium oxide, zirconium oxide, Florisil, or silica gel. Both polymers were retained, to different extents, within the columns. It is hypothesized that the polymers interact with the surfaces of the adsorbents and are adsorbed. Retention of isotactic polypropylene from 1,1,2,2-tetrachloroethane was in the order aluminium oxide > hydroxyapatite ≈ zirconium oxide ≈ Florisil ≈ silica gel. Recovery of polyethylene from 1,1,2,2-tetrachloroethane was almost the same on aluminium oxide, hydroxyapatite, zirconium oxide, and Florisil; it was more retained by silica gel. Polyethylene was usually more retained than polypropylene. Recovery of polyethylene from both chlorinated solvents was similar whereas recovery of polypropylene was better from 1,2,3-trichloropropane than from 1,1,2,2-tetrachloroethane. Both chlorinated solvents are toxic and may attack seals in a Waters 150C chromatograph. Moreover, the polymers may be chlorinated in these solvents. For these reasons they are not optimum solvents for routine analysis. This is the first time polyethylene and polypropylene have been found to be retained by adsorbents with pore diameters in the range 60–300 Å. Desorption of the retained polymers is possible with some polar solvents.     

Characterization of some commercial poly (styrene-divinylbenzene) copolymers for reversed-phase HPLC1

Summary The properties of the poly(styrene-divinylbenzene) copolymers PRP-1 and PLRP-S have been studied by infrared spectroscopy and chromatographic techniques. The following results were obtained: PRP-1 and PLRP-S are spectroscopically very similar. Their surfaces are chemically neither homogeneous nor stable during use. Retained nonpolar solutes should be eluted with a mobile phase containing tetrahydrofuran. Uncharged acids and anions can be chromatographed without difficulty. Cations of amines should be chromatographed only with a mobile phase of low pH. Uncharged amino-alcohols cannot be chromatographed without the addition of a competitor. Presented at the 16th International Symposium on Chromatography, Paris, France, September 1986     

A new isotherm equation for single-solute adsorption from dilute solutions on energetically heterogeneous solids

A new isotherm equation is proposed for describing single-solute adsorption from dilute solution on energetically heterogeneous solids. This equation comprises all isotherm equations being an extension of simpleLangmuir isotherm to single-solute adsorption on heterogeneous solids. The phenol adsorption data from dilute aqueous solutions on activated carbon are studied by using this new equation.

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Eine neue Isothermengleichung für die Adsorption aus verdünnten Einzelkomponentenlösungen auf energetisch heterogenen Festkörpern (Kurze Mitteilung)

Zusammenfassung Es wurde eine neue Isothermengleichung für die Adsorption aus verdünnten Einzelkomponentenlösungen auf energetisch heterogenen Festkörpern vorgeschlagen. Diese Gleichung schließt alle bisherigen Isothermengleichungen in sich ein, die Verallgemeinerungen der einfachenLangmuir-Isotherme für Adsorption auf heterogenen Festkörpern sind. Es wurden Daten der Adsorption von Phenol aus verdünnten Wasserlösungen auf aktivierte Kohle unter Verwendung der neuen Gleichung untersucht.

     

An isotherm equation for adsorption from binary liquid mixtures on solids involving surface heterogeneity and differences in molecular sizes of components and its numerical verification

An equation derived previously¹⁴ for adsorption from binary liquid mixtures composed of molecules of different sizes on heterogeneous solids has been reexamined. Verification of this equation by means of numerical simulation showed its applicability for describing the liquid adsorption onto weakly and strongly heterogeneous surfaces.

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Eine Isothermen-Gleichung für die Adsorption aus binären flüssigen Gemischen an heterogenen Oberflächen fester Körper unter Berücksichtigung der Differenzen in den Molekülgröen der Komponenten und ihre numerische Verifikation

Zusammenfassung Es wurde die früher¹⁴ abgeleitete Isothermen-Gleichung der Adsorption aus binären flüssigen Gemischen an heterogenen Oberflächen fester Körper abermals untersucht. Durch Computersimulation wurde gezeigt, daß diese Gleichung den obengenannten Prozeß, der sich sowohl an schwach wie auch an stark heterogenen Oberflächen vollzieht, gut beschreibt.

     

Syntheses of spherical silica and titania from alkoxides on a laboratory scale

Summary A process to synthesize silica and titania as spherical packing materials has been investigated on the laboratory scale by the sol-gel method. The silica and titania obtained were tested under normal-phase separation conditions for comparison of their retention characteristics silica witha a commercial. The silica was found to be similar in its retention behaviour to the commercial silica. The titania showed basic properties and strongly retained acidic compounds.     

HPLC Study of the Kinetics of Intramolecular Cyclization of Two New Phenyldiazene Molecules. Analytical Properties of the Resulting Liquid Crystals

A group of zeolites and a 3D nanoporous metal-organic material RPM-1 were tested as column packings for adsorption of isotactic polypropylene and linear polyethylene from dilute solutions. It was found that polyethylene is fully or partially retained from thermodynamically good solvents (1,1,2,2-tetrachloroethylene, 1,4-dimethylbenzene, diphenylether, 1,2-dichlorobenzene and 1,3-dichlorobenzene) at temperatures of 115 °C or 140 °C, when a specific type of zeolite with pore sizes 5–6 Å has been used as the column packing. Polypropylene was fully retained in another type of zeolite with pores of 7–12 Å, when diphenylether was used as the mobile phase. As far as known, this is the first system sorbent - mobile phase, where adsorption of polypropylene was observed.     

An HPLC study of tinidazole hydrolysis

Summary The high-performance liquid chromatographic (HPLC) method herein described allows the simultaneous determination of the hydrolysis kinetics of tinidazole and the formation kinetics of the hydrolysis products. Tinidazole is easily hydrolysed under basic conditions at raised temperature. The rate varies with the pH and the temperature of the solution, and the decomposition follows apparent first-order kinetics. The Arrheinius equation can be used to describe the effect of temperature on the half-life.     

The effect of some modifiers on the retention of aromatic hydrocarbons on untreated silica gel

Summary The retention parameters of benzene, naphthalene; anthracene and phenanthrene on untreated silica gel were determined in the presence of four modifiers: 1-methyl-2-pyrrolidone (MP), 4-formyl morpholine (FM), -butyrolactone (BL) and sulfolane (SF). Better column performance was found in the case of FM and MP only.     

HPLC study of the efficiency of extraction of phenolic compounds

Summary The rate of extraction of phenolic compounds in two different solvents has been studied by liquid chromatography (HPLC) under reverse phase, gradient elution conditions. The solvents were diethyl ether and ethyl acetate. The method has been applied to two natural samples, a white wine and apple pulp.     

Multilayer effects in adsorption of alcohols from benzene andn-heptane on silica gel

Experimental data for the title systems are compared with calculations based on theoretical adsorption parameters.

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Mehrschichteffekte bei der Adsorption von Alkoholen aus Benzol undn-Heptan auf Silicagel (Kurze Mitteilung)

Zusammenfassung Für die im Titel genannten Systeme werden experimentelle Daten mit Berechnungen verglichen, die auf theoretischen Parametern basieren.