Absence Of Buffer Research Articles

Ionophore based optical sensors using hydrophilic polymer matrix – Ratiometric, pH independent ion-selective optodes

Classical approach for cation selective optode sensing requires high lipophilicity of receptor matrix and optical transducer dye, its application is restricted to relatively narrow pH range. We propose an alternative approach to ion-selective optodes, benefiting from rather hydrophilic polymer - plasticized polycaprolacton. This results in presence of lipophlic (plasticizer) and hydrophilic (sample/polycaprolactone) domains within the nanoprobes proposed. In consequence, this approach allows benefiting from alternative optical transducer: Nile blue dye and its unique properties and in consequence to benefit from new optical transduction mechanism allowing ratiometric sensing with no restriction for the sample pH. The response mechanism involves ionophore and ion pair composed of cation-exchanger and Nile blue cation dissolved in the plasticizer phase. Analyte incorporation to the phase occurs on expense of dye cation release to the hydrophilic phase. Ultimately a red staining of plasticizer phase is observed due to incorporation of neutral dye molecules formed in course of spontaneous hydrolysis occurring in water phase. Thus herein proposed optodes offer observable emission change at two wavelengths (increase of intensity emission as well as decrease) allowing ratiometric sensing in a broad concentration range. Moreover, herein proposed approach is applicable both in acidic and alkaline media, also in the absence of buffer, thus it mitigates significant constrain of classical optodes. As model system potassium or calcium selective nanospheres were prepared.

Enriching Cations Using Electric Field Gradients Generated by Bipolar Electrodes in the Absence of Buffer

AbstractWe report that ionic current gradients and corresponding electric field gradients formed at bipolar electrodes are useful for enriching cations up to ∼350‐fold at specific locations in microfluidic devices. The enrichment mechanism is determined by collecting current data, measuring solution conductivity, and by performing pH indicator experiments. These data reveal the dynamic nature of the enrichment mechanism. Specifically, they show the complex relationship between the ionic current gradients formed at the bipolar electrode and the extent of cation enrichment. Finally, we demonstrate cation enrichment is possible in buffer‐free solutions containing up to 50.0 mM KCl. This finding is significant because it broadens the range of solutions in which membrane‐free, electrochemical separations using bipolar electrodes can be performed.

Optimization of a tannase-assisted process for obtaining teas rich in theaflavins from Camellia sinensis leaves

This work aimed at optimizing the extraction of theaflavins for the development of a potentially functional tea beverage using different technological parameters as factors. Green tea leaves treated with tannase provided a beverage with significant higher amount (4.7-fold) of theaflavin (TF) compared to the pure withered leaf fermentation. For black tea, the optimized process conditions to produce a beverage with high TF (0.269 μg/mL) concentration were: 6 g of leaves/400 mL, a low fermentation temperature of 25 °C with the absence of buffer and pH control, an intermediate fermentation time (60 min) and a relatively low aeration rate (0.8–1.0 L/min). The tea liquid produced under optimized fermentation conditions appears to be ideal for making a black tea beverage with surplus summer tea leaves and brings economic benefits.

Buffer Pka Impacts the Mechanism of Hydrogen Evolution in Water Catalyzed By a Cobalt Porphyrin-Peptide

A detailed study of the impact of buffer pKa (pKa 5.6 to 10.5) on electrochemical hydrogen evolution at constant pH catalyzed by CoMP11-Ac, a cobalt porphyrin peptide, is presented. The addition of buffer leads to a significant enhancement of the catalytic current of up to 20-fold relative to its value in absence of buffer. Two distinct catalytic regimes are identified based on the buffer pKa . In the presence of buffers with pKa ≤ 7.4 a fast catalysis regime limited by diffussion of buffer is reached. The catalytic half-wave potential (Eh ) shifts anodically (from -1.42 to -1.26 V vs Ag/AgCl/KCl(1M)) as the buffer pKa decreases from 7.4 to 5.6, proposed to result from fast Co(III)-H formation following the catalysis-initiating Co(II/I) reduction. With higher-pKa buffers (pKa > 7.7), an Eh = -1.42 V reflecting the potential of the Co(II/I) couple is maintained independent of the buffer pKa , consistent with a rate-limiting Co(III)-H formation under these conditions. We conclude that the buffer species pK a, even at constant pH, can have a large effect on both catalytic current and potential, as well as the rate-determining step of the reaction. Thus, buffer is a factor to consider in optimizing reaction conditions for hydrogen-evolving catalysis and for other proton-requiring reactions in water. Finally, buffer acids are shown to be a probe for studying hydrogen evolution mechanism in water.

Acid Evolution of Escherichia coli K-12 Eliminates Amino Acid Decarboxylases and Reregulates Catabolism.

Acid-adapted strains of Escherichia coli K-12 W3110 were obtained by serial culture in medium buffered at pH 4.6 (M. M. Harden, A. He, K. Creamer, M. W. Clark, I. Hamdallah, K. A. Martinez, R. L. Kresslein, S. P. Bush, and J. L. Slonczewski, Appl Environ Microbiol 81:1932-1941, 2015, https://doi.org/10.1128/AEM.03494-14). Revised genomic analysis of these strains revealed insertion sequence (IS)-driven insertions and deletions that knocked out regulators CadC (acid induction of lysine decarboxylase), GadX (acid induction of glutamate decarboxylase), and FNR (anaerobic regulator). Each acid-evolved strain showed loss of one or more amino acid decarboxylase systems, which normally help neutralize external acid (pH 5 to 6) and increase survival in extreme acid (pH 2). Strains from populations B11, H9, and F11 had an IS5 insertion or IS-mediated deletion in cadC, while population B11 had a point mutation affecting the arginine activator adiY The cadC and adiY mutants failed to neutralize acid in the presence of exogenous lysine or arginine. In strain B11-1, reversion of an rpoC (RNA polymerase) mutation partly restored arginine-dependent neutralization. All eight strains showed deletion or downregulation of the Gad acid fitness island. Strains with the Gad deletion lost the ability to produce GABA (gamma-aminobutyric acid) and failed to survive extreme acid. Transcriptome sequencing (RNA-seq) of strain B11-1 showed upregulated genes for catabolism of diverse substrates but downregulated acid stress genes (the biofilm regulator ariR, yhiM, and Gad). Other strains showed downregulation of H2 consumption mediated by hydrogenases (hya and hyb) which release acid. Strains F9-2 and F9-3 had a deletion of fnr and showed downregulation of FNR-dependent genes (dmsABC, frdABCD, hybABO, nikABCDE, and nrfAC). Overall, strains that had evolved in buffered acid showed loss or downregulation of systems that neutralize unbuffered acid and showed altered regulation of catabolism.IMPORTANCE Experimental evolution of an enteric bacterium under a narrow buffered range of acid pH leads to loss of genes that enhance fitness above or below the buffered pH range, including loss of enzymes that may raise external pH in the absence of buffer. Prominent modes of evolutionary change involve IS-mediated insertions and deletions that knock out key regulators. Over generations of acid stress, catabolism undergoes reregulation in ways that differ for each evolving strain.

Buffer-Free High Performance Liquid Chromatography Method for the Determination of <i>Theophylline</i> in Pharmaceutical Dosage Forms

Purpose : To develop and validate a simple, economical and reproducible high performance liquid chromatographic (HPLC) method for the determination of theophylline in pharmaceutical dosage forms. Method : Caffeine was used as the internal standard and reversed phase C-18 column was used to elute the drug and standard. The mobile phase was prepared by mixing water:acetonitrile:methanol at the ratio of 90:03:07 and the pH set at 4.6. Flow rate and ultraviolet (UV) detector were set at 1.0 mLmin-1 and 271 nm, respectively. The method was validated for linearity, recovery, accuracy, precision, specificity, and also for inter-day stability under laboratory conditions. Results : Retention time was 5.5 min. The limits of detection and quantification were 12.5 ngmL-1 and 100 ngmL-1, respectively. Recovery accuracy (%) for different concentrations ranged from 100.05 to 102.43; regression coefficient (R 2 ) of 0.994; precision RSD < 2.0, and negligible interference from common excipients. Conclusion : The method is simple, rapid, highly specific and suitable for the determination of theophylline. Absence of buffer and use of small quantity of organic solvents increase the life span of the column and reduce the cost of routine analysis of theophylline in industry. Keywords : Buffer-free, High performance liquid chromatography, Theophylline, Dosage form.

PVAc Microspheres via Semicontinuous Emulsion Polymerization: Synthesis, Characterization, Kinetic, and Surface Morphology Studies

Poly (vinyl acetate) (PVAc) latexes are economically important products with many desirable features. They are used as adhesives for porous materials in various processing stages of industries. Synthesis parameters have an important role on the physico-chemical properties of PVAc latexes such as: viscosity, average molecular weight, degree of polymerization, and surface morphology. In this work, PVAc was prepared via semicontinous emulsion polymerization (delayed monomer and initiator addition process) in the presence of ammonium persulfate (APS) as conventional anionic initiator, poly (vinyl alcohol) (PVA) as stabilizer, and sodium lauryl sulfate (SLS) as anionic emulsifier. The surface morphology of PVAc microspheres was, examined using a scanning electron microscope (SEM) and atomic force microscope (AFM). It is evident from the SEM photographs that all the particles became microspheres and are uniform in shape. The use of AFM for imaging of polyvinyl acetate confirms a typical sphere polymer. The effect of changes in the different parameters such as concentration of emulsifier, initiator concentration, and presence or absence of buffer on the vinyl acetate (VAc) conversion, the steady state polymerization rate, the viscosity-average molecular weight, and the final latex viscosity of synthesized PVAc were investigated. The effects of anionic emulsifier on the synthesized PVAc are also compared with those obtained by the nonionic emulsifier. The comparison indicated that the VAc monomer conversion and the final latex viscosity of the anionic system were higher than for the nonionic system but the viscosity-average polymer molecular weight of the anionic system was lower than that of the nonionic system. The adhesive strength of the synthesized PVAc latex was examined and the load and deflection data were reported.

Rational Design, Synthesis, and Spectroscopic and Photophysical Properties of a Visible‐Light‐Excitable, Ratiometric, Fluorescent Near‐Neutral pH Indicator Based on BODIPY

A visible-light-excitable, ratiometric, brightly fluorescent pH indicator for measurements in the pH range 5-7 has been designed and synthesized by conjugatively linking the BODIPY fluorophore at the 3-position to the pH-sensitive ligand imidazole through an ethenyl bridge. The probe is available as cell membrane permeable methyl ester 8-(4-carbomethoxyphenyl)-4,4-difluoro-3-[2-(1H-imidazol-4-yl)ethenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (I) and corresponding water-soluble sodium carboxylate, sodium 8-(4-carboxylatophenyl)-4,4-difluoro-3-[2-(1H-imidazol-4-yl)ethenyl]-1,5,7-trimethyl-3a,4a-diaza-4-bora-s-indacene (II). The fluorescence quantum yield Φ(f) of ester I is very high (0.8-1.0) in the organic solvents tested. The fluorescence lifetime (ca. 4 ns) of I in organic solvents with varying polarity/polarizability (from cyclohexane to acetonitrile) is independent of the solvent with a fluorescence rate constant k(f) of 2.4×10(8) s(-1). Probe I is readily loaded in the cytosol of live cells, where its high fluorescence intensity remains nearly constant over an extended time period. Water-soluble indicator II exhibits two acid-base equilibria in aqueous solution, characterized by pK(a) values of 6.0 and 12.6. The Φ(f) value of II in aqueous solution is high: 0.6 for the cationic and anionic forms of the imidazole ligand, and 0.8 for neutral imidazole. On protonation-deprotonation in the near-neutral pH range, UV/Vis absorption and fluorescence spectral shifts along with isosbestic and pseudo-isoemissive points are observed. This dual-excitation and dual-emission pH indicator emits intense green-yellow fluorescence at lower pH and intense orange fluorescence at higher pH. The influence of ionic strength and buffer concentration on the absorbance and steady-state fluorescence of II has also been investigated. The apparent pK(a) of the near-neutral acid-base equilibrium determined by spectrophotometric and fluorometric titration is nearly independent of the added buffer and salt concentration. In aqueous solution in the absence of buffer and in the pH range 5.20-7.45, dual exponential fluorescence decays are obtained with decay time τ(1)=4.3 ns for the cationic and τ(2)=3.3 ns for the neutral form of II. The excited-state proton exchange of II at near-neutral pH becomes reversible on addition of phosphate (H(2)PO(4)(-)/HPO(4)(2-)) buffer, and a pH-dependent change of the fluorescence decay times is induced. Global compartmental analysis of fluorescence decay traces collected as a function of pH and phosphate buffer concentration was used to recover values of the deactivation rate constants of the excited cationic (k(01)=2.4×10(8) s(-1)) and neutral (k(02)=3.0×10(8) s(-1)) forms of II.

Stabilizing effect of citrate buffer on the photolysis of riboflavin in aqueous solution

In the present investigation the photolysis of riboflavin (RF) in the presence of citrate species at pH 4.0–7.0 has been studied. A specific multicomponent spectrophotometric method has been used to assay RF in the presence of photoproducts during the reactions. The overall first-order rate constants (kobs) for the photolysis of RF range from 0.42 to 1.08×10–2min−1 in the region. The values of kobs have been found to decrease with an increase in citrate concentration indicating an inhibitory effect of these species on the rate of reaction. The second-order rate constants for the interaction of RF with total citrate species causing inhibition range from 1.79 to 5.65×10–3M−1min−1 at pH 4.0–7.0. The logk–pH profiles for the reactions at 0.2–1.0M citrate concentration show a gradual decrease in kobs and the value at 1.0M is more than half compared to that of k0, i.e., in the absence of buffer, at pH 5.0. Divalent citrate ions cause a decrease in RF fluorescence due to the quenching of the excited singlet state resulting in a decrease in the rate of reaction and consequently leading to the stabilization of RF solutions. The greater quenching of fluorescence at pH 4.0 compared to that of 7.0 is in accordance with the greater concentration of divalent citrate ions (99.6%) at that pH. The trivalent citrate ions exert a greater inhibitory effect on the rate of RF photolysis compared to that of the divalent citrate ions probably as a result of excited triplet state quenching. The values of second-order rate constants for the interaction of divalent and trivalent citrate ions are 0.44×10–2 and 1.06×10–3M–1min–1, respectively, indicating that the trivalent ions exert a greater stabilizing effect, compared to the divalent ions, on RF solutions.

ChemInform Abstract: Effects of Monoalkyl Phosphate Surfactants Upon the Acid Hydrolysis of Dioxolanes.

The pseudophase ion-exchange (PPIE) model was tested in the presence and absence of buffer for the acid-catalyzed hydrolysis of 2-(p-methoxyphenyl)-1,3-dioxolane (p-MPD) and 2-(2,4-dimethoxyphenyl)-2-ethyl-1,3-dioxoloane (2,4-DPED) in the presence of sodium monoalkyl phosphate surfactants. The maximum increase in the observed rate constant was about 10-fold for both substrates

Decrease in membrane hydraulic conductance of rhizodermal cells under nitrate deficit is related to acidification at the root surface

Barley seedlings (Hordeum vulgare L.) were grown on porous plates submerged in Knop medium at pH 6.0 (control) and in a similar nutrient solution where NO3− was replaced with Cl− (treatment); in some treatments Mes buffer (10–20 mM, pH 6.0) was added to the medium. In the absence of buffer, the pH of the medium shifted towards the alkaline region in the presence of NO3− and to the acidic region in the presence of Cl−, with the total shift of no more than 0.3 pH units per day. The replacement of NO3− with Cl− (in a buffer-free medium) decreased the hydraulic membrane conductance of rhizodermal cells (Lp) within a 4-h period; after one day Lp settled at approximately 50% of its initial value observed in untreated plants. When the removal of nitrate from the medium was accompanied by the addition of buffer, no changes in Lp were observed over a 1-day period. The perfusion of external solution (at a rate of 10 mm/s) made it possible to control pH in the proximity to root surface (pHs). These experiments showed that Lp was independent of the surface pH in the pHs range 7.0–5.0, whereas at pHs = 4.5 Lp decreased within 15 min to a steady-state level of about 50% of the control value. It is concluded that the reduction of Lp under nitrate deficit was related to acidification of the medium near the root surface. The acidic pH shift could be caused by the cessation of proton/nitrate symport and by activation of the plasmalemma H+-pump, related to changes in the cytosolic pH-stat.

Direct Synthesis of Nanoceria in Aqueous Polyhydroxyl Solutions

Nanoceria has shown excellent biomedical properties for potential use in treatment of diseases caused by reactive oxygen species (ROS). In the present work, the synthesis and redox chemistry of nanoceria in the presence of polyhydroxyl groups such as glucose and dextran are reported. The effect of both acidic and basic medium on the synthesis and oxidation state stability of nanoceria in the absence of buffer was examined using UV−vis spectroscopy and transmission electron microscopy. The basic and acidic mediums show a difference in the synthesis of nanoceria in terms of the size and structure without interfering with the redox chemistry. A comparison of pure and aqueous saccharides suspension of nanoceria in acid/base media undergoing redox transformation is also reported in this paper.

CYP3A4 Activity in the Presence of Organic Cosolvents, Ionic Liquids, or Water‐Immiscible Organic Solvents

P450 enzymes have attracted the attention of chemists for decades because of their impressive ability to catalyze the hydroxylation of inactivated C--H bonds. However, their use for synthesis in aqueous systems is limited. We report here a survey of the activity of purified human CYP3A4 in the presence of organic solvents or ionic liquids. We show that CYP3A4 tolerates only small amounts (<15 %) of water-miscible organic cosolvents or ionic liquids before its activity toward testosterone drops below detection. [BMIM][PF(6)] in a biphasic system was less detrimental to enzyme activity, with 20 % of the activity remaining in the presence of 15 % of this ionic liquid. CYP3A4 activity in the absence of buffer was only >or=10 % in solvents of the alkane series, with a minimum of 0.85 % water, and with the addition of sucrose and testosterone before enzyme lyophilization. Biphasic solvent systems were more promising, with approximately 85 % of the activity retained.

Cell-Directed Assembly of Lipid-Silica Nanostructures Providing Extended Cell Viability

Amphiphilic phospholipids were used to direct the formation of biocompatible, uniform silica nanostructures in the presence of Saccharomyces cerevisiae and bacterial cell lines. The cell surfaces organize multilayered phospholipid vesicles that interface coherently with the silica host and help relieve drying stresses that develop with conventional templates. These host structures maintain cell accessibility, addressability, and viability in the absence of buffer or an external fluidic architecture. The cell surfaces are accessible and can be used to localize added proteins, plasmids, and nanocrystals. Prolonged cell viability combined with reporter protein expression enabled stand-alone cell-based sensing.

Fluorescent measurement of the intracellular pH during sporulation of Saccharomyces cerevisiae.

This work reports the intracellular pH (pHi) dynamics of Saccharomyces cerevisiae cells in sporulation medium. Cells loaded with the pH-sensitive dye carboxy-seminaphthorhodafluor-1 (C.SNARF-1) exhibited an alkalization of the pHi following the extracellular pH during sporulation in the absence of buffer and almost no change in pHi or delta pH when sporulation was carried out in buffered medium. The results indicate that the pH gradient does not appear to be directly involved in the regulation of acetate uptake during sporulation. However, the alkalization of pHi by eliciting a decrease in metabolic fluxes could account for a lower demand for acetate.

Horseradish peroxidase immobilized on aluminum-pillared interlayered clay for the catalytic oxidation of phenolic wastewater

Horseradish peroxidase (HRP) was successfully immobilized on aluminum-pillared interlayered clay (Al-PILC) to obtain enzyme–clay complex for the treatment of wastewater polluted with phenolic compounds. The immobilized HRP exerted a perfect phenol removal by precipitation or transforming to other products over a broader pH range from 4.5 to 9.3. The addition of polyethylene glycol (PEG) could significantly enhance the phenol removal efficiency, and reduce the amount of immobilized enzyme required to achieve a high removal efficiency of over 90%. When the mass ratio of PEG/phenol and the molar ratio of hydrogen peroxide/phenol were 0.4 and 1.5, respectively, the oxidation of phenol could be completed within short retention time after the initiation of reaction in the absence of buffer. HRP immobilized on Al-PILC had better storage stability compared with free enzyme. However, the reusability of the immobilized enzyme was not very satisfactory. In the fourth repeated test, the immobilized enzyme lost its catalytic performance. Further research should focus on the improvement of reusability.

Oxidation of Good’s buffers by hydrogen peroxide

Good’s zwitterionic buffers are widely used in biological and biochemical research in which hydrogen peroxide is a solution component. This study was undertaken to determine whether Good’s buffers exhibit reactivity toward H 2O 2. It is found that H 2O 2 oxidizes both morpholine ring-containing buffers (e.g., Mops, Mes) and piperazine ring-containing zwitterionic buffers (e.g., Pipes, Hepes, and Epps) to produce their corresponding N-oxide forms. The percentage of oxidized buffer increases as the concentration of H 2O 2 increases. However, the rate of oxidation is relatively slow. For example, no oxidized Mops was detected 2 h after adding 0.1 M H 2O 2 to 0.1 M Mops (pH 7.0), and only 5.7% was oxidized after 24 h exposure to H 2O 2. Thus, although all of these buffers can be oxidized by H 2O 2, their slow reaction does not significantly perturb levels of H 2O 2 in the time frame and at the concentrations of most biochemical studies. Therefore, the previously reported rapid loss of H 2O 2 produced from the ferroxidase reaction of ferritin is unlikely due to reaction of H 2O 2 with buffer, a conclusion supported by the fact that H 2O 2 is also lost rapidly when the solution pH of the ferroxidase reaction is controlled by a pH stat apparatus in the absence of buffer.

Pharmacokinetics of the Antiviral Agent β- l -3′-Fluoro-2′,3′-Didehydro-2′,3′-Dideoxycytidine in Rhesus Monkeys

beta-L-3'-Fluoro-2',3'-didehydro-2',3'-dideoxycytidine (L-3'-Fd4C) is a potent and selective antiretroviral nucleoside with activity against lamivudine-resistant human immunodeficiency virus type 1 (HIV-1) and hepatitis B virus (HBV) in vitro. The pharmacokinetics of L-3'-Fd4C were characterized in three rhesus monkeys given single intravenous and oral doses. A two-compartment open model was fitted to the plasma and urine data. Plasma concentrations declined in a biexponential fashion with an average beta half-life of 12.45 h and central and steady-state volumes of distribution of 0.43 and 1.90 liters/kg, respectively. The average systemic and renal clearance values were 0.23 and 0.08 liters/kg, respectively, and the apparent mean terminal half-life of the oral dose was 12.5 h. The serum concentrations exceeded the 90% effective concentration value for lamivudine-resistant and wild-type HIV-1 after oral administrations. A large variation was observed in the oral bioavailability, which ranged from 15 to 31%. To determine whether the bioavailability may be improved by using a basic buffer solution, the oral dose was repeated to the same animals in a sodium bicarbonate solution. The bioavailability of L-3'-Fd4C administered with sodium bicarbonate was not significantly different from the bioavailability when the oral dose was administered in the absence of buffer (P = 0.49), suggesting that further development of this compound may warrant other approaches, such as development of a prodrug to improve its oral absorption.

Identifiability of the Model of the Intermolecular Excited-State Proton Exchange Reaction in the Presence of pH Buffer

In this report, we describe the fluorescence kinetics and the deterministic identifiability of the intermolecular excited-state proton dissociation reaction and how the addition of pH buffer affects both. In the absence of buffer, the time-resolved fluorescence decays as a biexponential function with decay times that are invariant with pH. The information that the proton association rate in the excited state is negligible in combination with fluorescence decay traces measured at different pH, excitation, or emission wavelengths does not provide enough useful information for the unique determination of the rate constants and the spectral parameters related to absorption and emission. Hence, the model of intermolecular excited-state proton dissociation in the absence of pH buffer is not identifiable. When a pH buffer is added to this photophysical system, the proton exchange becomes reversible and the decay times now are a function of pH and buffer concentration. The deterministic identifiability analysis shows that for the unique determination of all rate constants one should collect a minimum of three fluorescence decays characterized by at least two different pH and at least two different nonzero buffer concentrations. In addition to these three traces, minimally one biexponential fluorescence trace corresponding to the pH probe in the absence of buffer has to be recorded. The requirement that at least two of these traces should be collected at the same pH, excitation, and emission wavelengths leads to unique identifiability.

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 °C, on the endcapped C 18-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 1.54×10 −3 and 1.54×10 −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.