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Georges Guiochon

Publications and source records attributed to Georges Guiochon.

At least 73 records · Page 4Linked to original sources
PubMed2005

Effect of the surface heterogeneity of the stationary phase on the range of concentrations for linear chromatography.

The range of sample sizes within which linear chromatographic behavior is achieved in a column depends on the surface heterogeneity of the RPLC adsorbents. Two widely different commercial adsorbents were tested, the end-capped XTerra-C18 and the non-end-capped Resolve-C18. Adsorption isotherm data of caffeine were acquired by frontal analysis. These data were modeled and used to calculate the adsorption energy distribution (AED). This double analysis informs on the degree of surface heterogeneity. The best adsorption isotherm models are the bi-Langmuir and the tetra-Langmuir isotherms for XTerra and Resolve, respectively. Their respective AEDs are bimodal and quadrimodal distributions. This interpretation of the results and the actual presence of a low density of high-energy adsorption sites on Resolve-C18 were validated by measuring the dependence of the peak retention times on the size of caffeine samples (20-microL volume, concentrations 10, 1, 0.1, 1 x 10(-2), 1 x 10(-3), 1 x 10(-4), and 1 x 10(-5) g/L). The experimental chromatograms agree closely with the band profiles calculated from the best isotherms. On Resolve-C18, the retention time decreases by 40% when the sample concentration is increased from 1 x 10(-5) to 10 g/L. The decrease is only 10% for Xterra-C18 under the same conditions. The upper limit for linear behavior is 1 x 10(-4) g/L for the former adsorbent and 0.01 g/L for the latter. The presence of a few high-energy adsorption sites on Resolve-C18, with an adsorption energy 20 kJ/mol larger than that of the low-energy sites while the same difference on Xterra is only 5 kJ/mol, explains this difference. The existence of adsorption sites with a very high energy for certain compounds affects the reproducibility of their retention times and a rapid loss of efficiency in a sample size range within which linear behavior is incorrectly anticipated.

Adsorption↗
PubMed2005

Comparison of the thermodynamic properties of particulate and monolithic columns of molecularly imprinted copolymers.

A variety of polymerization techniques can be used to prepare molecularly imprinted copolymers (MIPs) for the purpose of the separation of enantiomers by HPLC. Unfortunately, the lack of thermodynamic and kinetic data characterizing the imprinted polymers prepared by these different techniques prevents the rational choice of the one most suited for a specific application. We investigated and compared the thermodynamic properties of copolymers imprinted for Fmoc-L-tryptophan and prepared by two different methods. The first was an in situ polymerization method that gives monolithic columns (monolithic MIPs), the second, a traditional method giving bulk MIPs. Examination of the thermodynamic properties on these two different MIPs showed that three types of binding sites coexist on their surface. The highest energy sites adsorb only the imprinted molecule or template. Most of the intermediate energy sites adsorb both the template and its antipode, although part of them may adsorb only the template. Finally, the lowest energy sites provide nonselective interactions of both the template and its antipode. On the nonimprinted copolymer, there are only two types of sites. The high-energy sites have a slightly lower energy that the intermediate sites of the MIPs, and the low-energy sites have properties close to those of the lowest energy sites on the MIPs. The monolithic MIPs have fewer nonselective sites than the bulk MIPs. However, the polar porogen that is needed to prepare the monolithic MIPs negatively affects the enantiomeric separation.

Journal Article↗
PubMed2004

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(-). The co-cation was K(+) or Na(+). Vacancy perturbations were measured on three concentration plateaus of propranolol hydrochloride, at 1.2, 12, and 24 mM, by injecting 100 microL of a pure mixture of methanol and water (40/60, v/v). Indirect detection of the solvent, the counteranion, the co-cation, and the chloride ion was carried out at 325 nm, a wavelength at which only propranolol responds. In a 1.2 mM propranolol hydrochloride solution, there is a 10-fold excess of counteranions and only a positive perturbation peak, due to the excluded co-cation and eluting before the column hold-up time, and a large vacancy peak, associated with propranolol, were recorded. Association between propranolol and the counteranion in excess determines the retention time of this second perturbation. The hydrophobicity of the complexes increases in the order Cl(-) < CH(3)COO(-) approximately HOOCC(2)H(4)COO(-) < NO(3)(-) < I(-) < HOOCCOHCOOHCOO(-) < (-)OOCC(2)H(4)COO(-) < SO(4)(2-) approximately HOOCCOHCOO(-)COO(-) < (-)OOCCOHCOO(-)COO(-). Propranolol retention is larger in the presence of the trivalent citrate anion than in that of the bivalent citrate, succinate, or sulfate anions. It is larger with these bivalent anions than with any monovalent anion. Equal concentration of propranolol hydrochloride and buffer in the mobile phase reveals five system peaks associated with the five components (solvent, counteranion, co-cation, chloride, propranolol molecules). In contrast with monovalent anions, bivalent anions (sulfate, succinate, citrate) or trivalent anions (citrate) cause a reversal of the elution order of the perturbation peaks of chloride anions and buffer molecules. This confirms a competition between chloride and buffer anions to form ion pairs with propranolol. The retention of the perturbation signal of the buffer increases with increasing anion charge because multivalent anions can bind to several molecules of propranolol. The perturbation measurements demonstrate the influence of the valence and hydrophobicity of the buffer on the retention of ionizable compounds. The inverse method allowed the derivation of the isotherm parameters from the overloaded band profiles of propranolol. These values confirm that adsorbate-adsorbate interactions increase with increasing valence of the anions.

Journal Article↗
PubMed2004

Adsorption of the enantiomers of 2,2,2-trifluoro-1-(9-anthryl)-ethanol on silica-bonded chiral quinidine-carbamate.

The adsorption isotherms of the enantiomers of 2,2,2-trifluoro-1-(9-anthryl)-ethanol from a toluene-acetonitrile solution onto a Chiris Chiral AX:QD1 column were measured using the pulse method. The isotherm data were modeled with a bi-Langmuir isotherm model, indicating the presence of two different types of adsorption sites on this stationary phase, nonselective and enantioselective sites. The latter are homogeneous but interact with both enantiomers, albeit with different energies. The thermodynamic characteristics of these two types of sites were characterized by their adsorption constants and saturation capacities and by the influence of the temperature on these different parameters.

Adsorption↗
PubMed2004

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. The different values obtained are in close agreement. They allow a quantitative investigation of the separate properties of the low- and the high-energy sites on the adsorbent surface. Increasing the temperature decreases the saturation capacity of the low-energy adsorption sites and the adsorption constant of the high-energy sites. In contrast, increasing the temperature does not cause any significant changes in either the saturation capacity of the high-energy sites or the adsorption constant of the low-energy sites.

Adsorption↗
PubMed2004

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). The four sets of isotherm data are all well accounted for using the bi-Moreau model. However, the isotherms of the two ions behave differently at high concentrations. The initial behaviors of all the isotherms are antilangmuirian but remain so in a much wider concentration range for the cation than for the anion, due to its stronger adsorbate-adsorbate interactions on the low-energy adsorption sites. The retention times of both ions increase with increasing concentration of neutral salt in the mobile phase, suggesting the formation of ion-pair complexes, with Cl- for the cation and with Na+ for the anion. The adsorbate-adsorbate interactions vanish in the presence of salt and the bi-Moreau isotherm model tends toward a bi-Langmuir model. Differences in adsorption behavior are also observed between the cation and the anion when bivalent inorganic anions and cations, respectively, are dissolved in the mobile phase. High concentration band profiles of 1-naphthalene sulfonic acid are langmuirian, except in the presence of a trivalent cation, while those of propranolol are antilangmuirian under certain conditions even with uni- or divalent cations.

Adsorption↗
PubMed2004

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. These data fit best to the Bi-Moreau model. Large concentration band profiles of propranolol were recorded with mobile phases containing increasing KCl concentrations (0, 0.002, 0.005, 0.01, 0.05, 0.1 and 0.2 M) and the best values of the isotherm coefficients were determined using the numerical solution of the inverse problem of chromatography. The general effect of a dissociated salt in the mobile phase was the same as the one observed earlier with XTerra-C18 and Symmetry-C18. However, obvious differences were observed for the shape of the band profiles recorded at low column loading (1.5 g/L, 250 microL injected). A long shoulder is visible at all salt concentrations and the band broadening is maximum at low salt concentrations. A slow mass transfer kinetics on the high-energy sites of the bi-Moreau model might explain this original shape. Five other salts (NaCl, CsCl, KNO3, CaCl2 and Na2SO4) were also used at the same ionic strength (J = 0.2 M). As many different band profiles were observed, suggesting that specific solute-salt interactions take place in the adsorbed phase.

Adsorption↗
PubMed2004

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 0.2 and 6.0 g/L, respectively. This precludes the modeling of these data with a simple convex-upward isotherm (e.g., Langmuir). The adsorption energy distribution or relationship between the number of sites on the adsorbent surface and the energy of adsorption on these sites was calculated by assuming Moreau isotherm behavior (S-shaped isotherm). This model has never been applied to describe the surface heterogeneity of any RPLC adsorbent. The calculation converged toward a bimodal energy distribution. Accordingly, the bi-Moreau model is the simplest theoretical model accounting for the adsorption data of propranolol from a mobile phase without salt. The complex-overloaded band profiles of propranolol measured in the presence of increasing concentrations of a supporting salt (KCl) in the mobile phase demonstrate that the same isotherm model applies also under these conditions, as was merely assumed in a previous work. The elution band profiles of propranolol calculated with the bi-Moreau isotherm model for solutions of salts of different natures (CaCl2, CsCl, Na2SO4) in the same mobile phase agree very well with the experimental band profiles.

Adsorption↗
PubMed2004

Isothermal microcalorimetric study of the pH dependence of the interactions between a cellulase and a beta-blocker.

The influence of the pH on the complexation equilibria between (S)- or (R)-alprenolol and the cellulase Cel7A was investigated by isothermal titration calorimetry. The results obtained agree with those of previous, similar studies of the same equilibria in which the protein was immobilized on silica particles, packed in a chromatographic column. The association constant and the complexation enthalpy and entropy of the (S)-enantiomer increase with increasing pH. For (R)-alprenolol, the binding is endothermic at all pH values. Thus, for both enantiomers in the pH range 5.5-6.8, the binding is an entropically driven process.

Adrenergic beta-Antagonists↗
PubMed2004

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 0.1 K for the temperature, 0.1% for the mobile phase composition and 0.001 mL/min for the flow rate. The best isotherm model was shown to be the tri-Langmuir isotherm. Random errors were calculated and shown to agree with experimental results. Overloaded band profiles of phenol were acquired at low (sample size, 100 microL, concentration 3 g/L) and high (same sample size, concentration 60 g/L) loadings, at seven temperatures (298, 300, 302, 303, 304, 306, and 308 K), for seven mobile phase compositions (methanol 16, 18, 19, 20, 21, 22, and 24%), and with seven mobile phase flow rates (0.95, 0.97, 0.99, 1.00, 1.01, 1.03, and 1.05 mL/min), always keeping two experimental parameters at the values selected for the FA runs. Assuming that the isotherm model stays the same, the inverse method (IM) was used to derive the isotherm parameters in each case. Temperature affects the equilibrium constants according to Van't Hoff law. A temperature change of 1 K around 303 K causes a relative variation of 1.5% of the high-energy adsorption constant b3 and of 0.6% of the saturation capacity q3. The isotherm parameters are very sensitive to the mobile phase composition, especially the highest energy mode. Both adsorption constants b2 and b3 follow the linear strength solvent model (LSSM). A methanol volume fraction change of 1% causes a relative decrease of 3.2 and 5.0% of b2 and b3, respectively and a 2% decrease of the saturation capacity q3. Finally, flow rate changes affect only the saturation capacities. A flow rate change of 1 % causes a 2% change in the saturation capacity parameters.

Adsorption↗
PubMed2004

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 < 6.75, using four buffers (phosphate, acetate, phthalate, and succinate), at three concentrations, 6, 20, and 60 mM. The results showed that the propranolol cation was eluted as an ion-pair with the buffer counter-anion. A similar study was carried out with Symmetry-C18 and Xterra-C18. Two additional buffers, formate and citrate, were also used. Propranolol elution band profiles were recorded for a small (less than 1 microg) and a large (375 microg) sample size. The results are similar to those obtained with Kromasil and confirm earlier conclusions. The buffer concentration, not its pH, controls the retention time of propranolol, in agreement with the chaotropic model. The retention factor depends also on the nature of the buffer, particularly on its valence, and on the hydrophobicity of the basic anion. With the monovalent anions HCOO- (pH 3.75), H2PO4- (pH 2.75), HOOC-Ph-COO- (pH 2.75), HOOC-CH2-CH2-COO- (pH 4.16), CH3COO- (pH 4.75) and HOOC-CHCOOH-COO- (pH 3.14), at moderate loadings, and for the two larger buffer concentrations, the band profiles are well accounted for by a simple bi-Langmuir isotherm model (no adsorbate-adsorbate interactions). By contrast, these profiles are accounted for by a bi-Moreau isotherm model (i.e., with significant adsorbate-adsorbate interactions) with the bivalent anions -OOC-Ph-COO- (pH 4.75), -OOC-CH2-CH2-COO- (pH 5.61), HPO4(2-) (pH 6.75), and HOOC-CHCOO(-)-COO- (pH 4.77) and with the trivalent anion -OOC-CHCOO(-)-COO- (pH 6.39). The best values of the isotherm parameters were determined using the inverse method. The saturation capacity and the equilibrium constant on the low-energy sites increase with increasing buffer concentration, a result consistent with the formation in the mobile phase of a hydrophobic complex between the propranolol cation and the buffer anion. With bivalent and trivalent anions, adsorbate-adsorbate interactions are strong on the low-energy sites but they remain negligible on the high-energy sites. The density of the high energy sites is lower and the equilibrium constant on the low-energy sites are both higher with the bivalent and the trivalent buffer anions than with the univalent buffer anions. These results are consistent with the formation of a 2:1 and a 3:1 propranolol-buffer complex with the bivalent and the trivalent anions, respectively.

Adsorption↗
PubMed2004

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 < 6.75, using four buffers (phosphate, acetate, phthalate, and succinate), at three concentrations, 6, 20, and 60 mM. The propranolol band profiles were recorded for three sample sizes, less than 1 microg and 375 microg (sample less concentrated than the buffer), and 7500 microg (band more concentrated than the buffer). Results showed that the buffer concentration, not its pH, controls the retention time of propranolol, in agreement with the chaotropic model. The retention factor depends also on the nature of the buffer, particularly the valence of the basic anion. At moderate loading, the band profiles are well accounted for by a simple bilangmuir model (no adsorbate-adsorbate interactions) with the monovalent anions H2PO4- (pH 2.75), HOOC-Ph-COO- (pH 2.75), HOOC-CH2-CH2-COO- (pH 4.16) and CH3COO- (pH 4.75), and by a bimoreau model (significant adsorbate-adsorbate interactions) with the bivalent anions OOC-Ph-COO- (pH 4.75), OOC-CH2-CH2-COO- (pH 5.61) and HPO4(2-) (pH 6.75). The isotherm were determined using the inverse method. The results show that both the saturation capacity and the equilibrium constant on the low-energy sites increase with increasing buffer concentration, a result similar to that observed with neutral salts. For bivalent anions, the adsorbate-adsorbate interactions are much stronger on the low than on the high energy sites. The density of high energy sites is lower and the equilibrium constant on the low energy sites are higher with bivalent than with univalent anions. These results are consistent with the formation of a propranolol-buffer (2:1) complex with bivalent anions.

Adsorption↗
PubMed2004

Evaluation of the uniformity of analytical-size chromatography columns prepared by the downward packing of particulate slurries.

The axial heterogeneity of downward slurry-packed chromatography columns was evaluated. A series of columns were prepared that varied in total length from 5 to 30 cm. Each column was packed in stainless steel tubing that was sectioned to allow the column to be divided into 5-cm sections after packing. Each 5-cm section of these columns was then tested for chromatographic performance. In total, 22 such column sections were tested. The results of the study show that the consolidation of the packed bed is a very complex problem, yet systematic variations of the column performance were observed, depending on the location of the section tested from within the entire column. For example, when columns longer than 20 cm were packed, the most homogeneous and best performing section of the column was the lower midsection. Whereas for columns shorter than 20 cm in length, the best sectioned region of the bed was the lower and outlet region. In all cases, the most poorly packed region of the bed was the column inlet section, irrespective of the bed length. The phenomenon associated with this axial heterogeneity undoubtedly results from a complex interplay between wall friction, particle momentum, and the pressure pulsations resulting from the packing process.

Journal Article↗
PubMed2004

Effect of the ionic strength of salts on retention and overloading behavior of ionizable compounds in reversed-phase liquid chromatography I. XTerra-C18.

The influence of the salt concentration (potassium chloride) on the retention and overloading behavior of the propranolol cation (R'-NH2+ -R) on an XTerra-C18 column, in a methanol:water solution, was investigated. The adsorption isotherm data were first determined by frontal analysis (FA) for a mobile phase without salt (25% methanol, v/v). It was shown that the adsorption energy distribution calculated from these raw adsorption data is bimodal and that the isotherm model that best accounts for these data is the bi-Moreau model. Assuming that the addition of a salt into the mobile phase changes the numerical values of the parameters of the isotherm model, not its mathematical form, we used the inverse method (IM) of chromatography to determine the isotherm with seven salt concentrations in the mobile phase (40% methanol, v/v; 0, 0.002, 0.005, 0.01, 0.05, 0.1 and 0.2 M). The saturation capacities of the model increase, q(s,1) by a factor two and q(s,2) by a factor four, with increasing salt concentration in the range studied while the adsorption constant b1 increases four times and b2 decreases four times. Adsorbate-adsorbate interactions vanish in the presence of salt, consistent with results obtained previously on a C18-Kromasil column. Finally, besides the ionic strength of the solution, the size, valence, and nature of the salt ions affect the thermodynamic as well as the mass transfer kinetics of the adsorption mechanism of propranolol on the XTerra column.

Adsorption↗
PubMed2004

Effect of the ionic strength of salts on retention and overloading behavior of ionizable compounds in reversed-phase liquid chromatography II. Symmetry-C18.

In a companion paper, we describe the influence of the concentration and the nature of 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. The same experiments were repeated on a Symmetry-C18 column to compare the adsorption mechanisms of this ionic compound on these two very different RPLC systems. Frontal analysis (FA) measurements were first carried out to determine the best isotherm model accounting for the adsorption behavior of propranolol hydrochloride on Symmetry with a mobile phase without salt (and only 25% methanol to compensate for the low retention in the absence of salt). The adsorption data were best modeled by the bi-Moreau model. Large concentration band profiles of propranolol were recorded with mobile phases having increasing KCl concentrations (0, 0.002, 0.005, 0.01, 0.05, 0.1 and 0.2 M) and the best values of the isotherm coefficients were determined by the inverse method (IM) of chromatography. The general effect of a dissociated salt in the mobile phase was the same as the one observed earlier with XTerra-C18. Increasing the salt concentration increases the two saturation capacities of the adsorbent and the adsorption constant on the low-energy sites. The adsorption constant on the high-energy sites decreases and the adsorbate-adsorbate interactions tend to vanish with increasing salt concentration of the mobile phase. The saturation capacities decrease with increasing radius of the monovalent cation (Na+, K+, Cs+, etc.). Using sulfate as a bivalent anion (Na2SO4) affects markedly the adsorption equilibrium: the saturation capacities are drastically reduced, the high-energy sites nearly disappear while the adsorption constant and the adsorbate-adsorbate interactions on the low-energy sites increase strongly. The complexity of the thermodynamics in solution might explain the different influences of these salts on the adsorption behavior.

Adsorption↗
PubMed2004

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) = 0.20 M and pH = 5.9. In both cases, 33 isotherm data points were acquired by frontal analysis (FA), to achieve an accurate description of the isotherms in the concentration range between 1.54 x 10(-3) and 1.54 x 10(-1) mol/l of propranolol. The isotherms obtained were best described by a bi-Langmuir and a bi-Moreau isotherm model, depending on whether the mobile phase was buffered or not. This shows that the adsorption of propranolol takes place on two different types of sites, a behavior similar to the one already observed with phenol and caffeine on the same column. The presence of the buffer in the mobile phase drastically changes the adsorption mechanism of propranolol. Weak adsorbate-adsorbate interactions (two and three times RT on the low- and the high-energy sites, respectively) take place in the absence of buffer but vanish when the mobile phase is buffered. As expected, the adsorption constants on the abundant low-energy sites with or without buffer are comparable because the mobile phase composition was adjusted to give similar retention times in the two cases. On the other hand, the adsorption of propranolol on the high-energy sites is stronger in presence of the buffer. The difference probably comes from ion-pair formation in the adsorbed phase between the propranolol cation and the acetate anion. The change in total saturation capacity of the adsorbent (22%) compared to that for phenol is explained by the difference in methanol content of the mobile phase.

Adsorption↗