Elution of propranolol as an ion-pair complex by buffer solutions on C18-silica.

Propranolol (pK(a) = 9.4) was eluted on C(18)-bonded Kromasil, equilibrated with buffer solutions of methanol and water (40/60, v/v) containing a constant concentration of a counteranion (12 mM). Nine different counteranions were studied: Cl(-), I(-), NO(3)(-), SO(4)(2-), CH(3)COO(-), HOOCC(2)H(4)COO(-), (-)OOCC(2)H(4)COO(-), HOOCCOHCOOHCOO(-), HOOCCOHCOO(-)COO(-), and (-)OOCCOHCOO(-)COO(-).

Adsorption isotherms of the fullerenes C60 and C70 on a tetraphenylporphyrin-bonded silica.

The single-component adsorption isotherms of the C60 (from 0 to 15 g/L) and C70 (from 0 to 8 g/L) buckminsterfullerenes on a tetraphenylporphyrin-bonded silica were acquired by frontal analysis, using a solution of toluene-1-methylnaphthalene (40:60, v/v) as the mobile phase. The best isotherm model derived from the fitting of these adsorption data was the bi-Langmuir model, a choice supported by the bimodal affinity energy distribution (AED) obtained for C60. The isotherm parameters derived from the inverse method (IM) of isotherm determination (by fitting calculated profiles to experimental overloaded band profiles of C60 and C70) are in very good agreement with those derived from the FA data.

Effect of the temperature on the isotherm parameters of phenol in reversed-phase liquid chromatography.

Adsorption isotherm data of phenol from an aqueous solution of methanol onto a C18-bonded silica (Symmetry-C18) were acquired by frontal analysis (FA) at six different temperatures, in a wide concentration range. The non-linear fitting of these data provided the bi-Langmuir model as best isotherm model, a conclusion further supported by the results of the calculation of the affinity energy distribution (AED). The isotherm parameters were obtained using several methods, the fitting of FA isotherm data, the calculation of the AED, and the inverse method, that uses overloaded elution band profiles.

Effect of the ionic strength of the solution and the nature of its ions on the adsorption mechanism of ionic species in RPLC III. Equilibrium isotherms and overloaded band profiles on Kromasil-C18.

In two companion papers, we have described the influence of the concentration and the nature of completely dissociated salts dissolved in the mobile phase (methanol:water, 40:60, v/v) on the adsorption behavior of propranolol (R'-NH2+-R, Cl-) on XTerra-C18 and on Symmetry-C18. The same experiments were repeated on a Kromasil-C18 column to compare the adsorption behavior of this ionic compound on these three different RPLC systems. The adsorption data of propranolol hydrochloride were first measured by frontal analysis (FA) using a mobile phase without salt.

Comparison between the adsorption behaviors of an organic cation and an organic anion on several reversed-phase liquid chromatography adsorbents.

Adsorption data of an organic cation (propranololium chloride) and an organic anion (sodium 1-naphthalene sulfonate) were measured by frontal analysis on two RPLC adsorbents, Symmetry-C18 and XTerra-C18, with aqueous solutions of methanol as the mobile phases. The influence of supporting neutral salts on the adsorption behavior of these two ions are compared. The Henry constants are close (H approximately 5).

Accuracy and precision of adsorption isotherm parameters measured by dynamic HPLC methods.

The fluctuations of the column temperature, the composition and the flow rate of the mobile phase affect the accuracy and precision of the adsorption isotherm parameters measured by dynamic HPLC methods. Experimental data were acquired by frontal analysis (FA) for phenol in equilibrium between C18-bonded Symmetry and a methanol:water mixture (20:80, v/v), at 303 K and a flow rate of 1 mL/min. The fluctuations of the experimental parameters were 0.

Retention of ionizable compounds in reversed-phase liquid chromatography. Effect of the ionic strength of the mobile phase and the nature of the salts used on the overloading behavior.

The retention mechanism of the protonated cation in propranolol chloride on C18-Xterra was investigated using mobile phases of various compositions. Accurate adsorption data were measured by frontal analysis, with a mixture of methanol and water (25% methanol), with no salt, as the mobile phase. The experimental isotherm has at least two inflection points, at concentrations of about 0.

Effect of the pH, the concentration and the nature of the buffer on the adsorption mechanism of an ionic compound in reversed-phase liquid chromatography. II. Analytical and overloaded band profiles on Symmetry-C18 and Xterra-C18.

In a previous report, the influence of the pH, the concentration, and the nature of the buffer on the retention and overloading behavior of propranolol (pKa = 9.45) was studied on Kromasil-C18 at 2.75 < pH < 6.

Role of the buffer in retention and adsorption mechanism of ionic species in reversed-phase liquid chromatography. I. Analytical and overloaded band profiles on Kromasil-C18.

The influence of the pH, the concentration, and the nature of the buffer on the retention and overloading behavior of propranolol (pKa = 9.25) on Kromasil-C18 was studied at 2.75 < pH < 6.

Influence of a buffered solution on the adsorption isotherm and overloaded band profiles of an ionizable compound.

The overloaded band profiles and the adsorption isotherms of propranolol were acquired at 23 degrees C, on the endcapped C18-Kromasil stationary phase, using two aqueous solutions of methanol as the mobile phase. The first solution contained 40% methanol and no buffer. The second contained an aqueous acetate buffer at C(buffer) = 0.

Band splitting in overloaded isocratic elution chromatography III. Modeling of adsorbate-adsorbate interactions by a two-component extension of a BET kinetic isotherm model.

A new two-component competitive adsorption model was derived to account for the competitive adsorption data of mixtures of ethylbenzoate and 4-tert-butylphenol, on a C18-Kromasil column under RPLC conditions (mobile phase, methanol/water, 62/38, v/v). The derivation is based on kinetic arguments and is an extension to multicomponent systems of the single-component BET isotherm. The model assumes that the molecules of the first compound (A) can adsorb on layers made of molecules of either A or B, while molecules of B can only adsorb on layers made of molecules of A.

Heterogeneity of the surface energy on unused C18-chromolith adsorbents in reversed-phase liquid chromatography.

Single-component adsorption isotherm data were acquired by frontal analysis (FA) for phenol and caffeine on a new C18-Chromolith column (Merck, Darmstadt, Germany), using a water-rich mobile phase (methanol/water, 15/85, v/v). These data were modeled for best agreement between the experimental data points and the adsorption isotherm model. The adsorption-energy distributions, based on the expectation-maximization (EM) procedure, were also derived and used for the selection of the best isotherm model.

Physical origin of peak tailing on C18-bonded silica in reversed-phase liquid chromatography.

Single component isotherm data of caffeine and phenol were acquired on two different stationary phases for RPLC, using a methanol/water solution (25%, v/v, methanol) as the mobile phase. The columns were the non-endcapped Waters Resolve-C18, and the Waters XTerra MS C18. Both columns exhibit similar C18 -chain densities (2.

Single-component shock layer analysis in elution chromatography.

One of the fundamental results of the theory of nonlinear chromatography is that a propagation velocity is associated with each concentration. This velocity is related to the slope of the isotherm at the corresponding concentration. It follows that if a continuous concentration gradient is injected into a column, the gradient profile will not propagate in a mere translation but will progressively change shape.

Repeatability and reproducibility of high-concentration data in reversed-phase liquid chromatography. III. Isotherm reproducibility on Kromasil C18.

Single component equilibrium isotherms of six compounds (aniline, caffeine, ethylbenzene, phenol, propranolol, and theophylline) were determined by the inverse method on 10 Kromasil-C18 columns, using water-methanol solutions as the mobile phase. This method offers an economic and fast isotherm determination by means of the overloaded band profiles of the compounds. Five out of the ten columns used in this test come from the same batch whilst the other five columns represent five additional batches.

Reproducibility of low and high concentration data in reversed-phase liquid chromatography. II. Overloaded band profiles on Chromolith-C18.

Single-component adsorption isotherm data were acquired by frontal analysis (FA) for six low molecular weight compounds (phenol, aniline, caffeine, o-toluidine, p-toluidine and propylbenzoate) on one Chromolith-C18 column (#30, Merck, Darmstadt, Germany), using different methanol:water solutions (composition between 60/40 and 15/85 v/v, depending on the solute) as the mobile phase. These data were modeled for best agreement between the experimental data points and the adsorption isotherm model. The adsorption-energy distributions were also derived and used for the selection of the best isotherm model.

Moment analysis of mass-transfer kinetics in C18-silica monolithic columns.

The moment analysis of elution peak profiles based on new moment equations provides information on the mass-transfer characteristics of C(18)-silica monolithic columns. The flow rate dependence of the HETP data was analyzed using the generalized van Deemter equation, after correction of these data by subtraction of the external mass-transfer contribution to band broadening. Kinetic parameters and diffusion coefficients related to the mass-transfer processes in monolithic columns were derived by taking advantage of the different flow velocity dependence of their contributions to band broadening.

Surface heterogeneity of six commercial brands of end-capped C18-bonded silica. RPLC separations.

Single component adsorption isotherms of phenol and caffeine were measured on six different commercial brands of end-capped C(18)-bonded silica columns (five monomeric bonded phases: Kromasil, Waters Symmetry, Phenomenex, Hypersil, and Chromolith from Merck; one polymeric bonded phase, Vydac) with the same methanol/water solution (30/70, v/v) as the mobile phase. Adsorption data were acquired by frontal analysis (FA) for all these columns in the same way. Depending on their solubility in the mobile phase, the concentrations used ranged between 1 and 100 g/L and between 0.

Overloaded gradient elution chromatography on heterogeneous adsorbents in reversed-phase liquid chromatography.

Overloaded band profiles of phenol were measured on a C18-Kromasil column in gradient elution conditions. The mobile phase used was a mixture of methanol and water. The volume fraction of methanol was allowed to vary between 0 and 0.

Gender differences in antiretroviral drug-related adipose tissue alterations. Women are at higher risk than men and develop particular lipodystrophy patterns.

Adipose tissue alterations (ATAs) were clinically assessed in 2258 HIV-1-infected outpatients consecutively observed in 6 Italian clinical centers and were found to be present in 29.5% of the men and 41.9% of the women.

Adsorption-desorption isotherm hysteresis of phenol on a C18-bonded surface.

Single component adsorption and desorption isotherms of phenol were measured on a high-efficiency Kromasil-C18 column (N = 15000 theoretical plates) with pure water as the mobile phase. Adsorption isotherm data were acquired by frontal analysis (FA) for seven plateau concentrations distributed over the whole accessible range of phenol concentration in pure water (5, 10, 15, 20, 25, 40, and 60 g/l). Desorption isotherm data were derived from the corresponding rear boundaries, using frontal analysis by characteristic points (FACP).

Band splitting in overloaded isocratic elution chromatography II. New competitive adsorption isotherms.

The equations of two new binary competitive isotherms models are derived. The first of these models assumes that the isotherms of the two pure, single compounds have distinct monolayer capacities. Its derivation is based on kinetic arguments.

Band splitting in overloaded isocratic elution chromatography I. The experimental evidence.

A series of samples of increasing volume (from 0.001 to 4.0 cm3), containing the same constant concentration (40 g/l) of two simple compounds, ethylbenzoate and 4-tert.

Study of the competitive isotherm model and the mass transfer kinetics for a BET binary system.

The competitive adsorption behavior of the binary mixture of phenetole (ethoxy-benzene) and propyl benzoate in a reversed-phase system was investigated. The adsorption equilibrium data of the single-component systems were acquired by frontal analysis. The same data for binary mixtures were acquired by the perturbation method.

Repeatability and reproducibility of high concentration data in reversed-phase liquid chromatography. I. Overloaded band profiles on Kromasil-C18.

Single-component adsorption-isotherm data were acquired by frontal analysis (FA) for six low-molecular-mass compounds (phenol, aniline, caffeine, theophylline, ethylbenzene and propranolol) on one Kromasil-C18 column, using water-methanol solutions (between 70:30 and 20:80, v/v) as the mobile phase. Propranolol data were also acquired using an acetate buffer (0.2 M) instead of water.