Showing papers on "Buffer solution published in 1992"

Chiral separation of β-amino alcohols by capillary electrophoresis using cyclodextrins as buffer additives. I. Effect of varying operating parameters

Abstract: Capillary electrophoresis has been used for the chiral analysis of two β-amino alcohol pharmaceutical compounds. Capillary zone electrophoresis conditions were used with β-cyclodextrin as a chiral mobile phase additive. The effects of variation of β-cyclodextrin concentration, temperature, pH, background electrolyte composition and concentration have been investigated. Optimum separations were achieved for clenbuterol using β-cyclodextrin at its solubility limit (16mM), the lowest practicable temperature (19°C), pH 4.0 and an electrolyte solution with a high ionic strength prepared from 0.1 M citric acid and 0.3 M Na2HPO4. For the development compound picumeterol and its (S)-enationmer, the optimum pH 4.0 buffer was prepared from 0.1 M citric acid and 0.2 M sodium acetate. Baseline separation with resolution greater than 2 was achieved for both compounds.

Degradation of nonalternating poly(ester amides)

Abstract: Two types of poly(ester-amide)s were prepared by convenient methods for degradation studies. Both were found to be degradable under attack of Fusarium monoliforme. These copolymers are also degradable by hydrolysis in pH 7.4 buffer solution, however, at much slower rates

Separation of boron-complexed diol compounds using high-performance capillary electrophoresis

Abstract: In this study, borate is shown to be key in the high-performance capillary electrophoretic (HPCE) separation of several biologically-active molecules differing only by a single hydroxyl group with no change in net charge. Separation of several paired compounds is minimal or nonexistent in 100 mM tricine buffer at pH 8.4, while identical analysis with 100 mM borate buffer led to baseline resolution on less than 10 min, most likely due to complexation of borate with the molecules containing a cis-diol

Temperature programming in capillary zone electrophoresis

Abstract: A now type of selectivity in capillary zone electrophoresis (CZE) based on temperature programming is presented. By using a buffer system with a large temperature coefficient, e.g. Tris buffer, the pH within the capillary can be adjusted in situ by simply controlling the temperature of the capillary. The electromigration behavior of weak acids is found to be influenced by both temperature-induced pH changes and viscosity changes. The effect of pH on the electrophoretic mobilities of analytes is most significant if the range of pH change matches the acidity constants, pK{sub a}, of the analytes. The implementation of temperature programming in both temporal and positional modes in CZE are illustrated by the separation of a mixture of fluorescent organic acids. 29 refs., 4 figs., 2 tabs.

Properties of Amylase Immobilized on a New Reversibly Soluble-Insoluble Polymer and Its Application to Repeated Hydrolysis of Soluble Starch

Abstract: A copolymer of glycidyl methacrylate (GMA) and N-isopropyl acrylamide (NIPAM) forms a reversibly soluble-insoluble (S-IS) polymer (GMA-NIPAM), whose solubility changes with the temperature of the solution An amylase (Dabiase) was immobilized on GMA-NIPAN under alkaline conditions The specific activity of Dabiase immobilized on GMA-NIPAM (D-GN) for saccharification of soluble starch was 90% that of native Dabiase and higher than that of conventional solid immobilized enzymes D-GN was soluble below 32°C but insoluble above 44°C When NaCl was added to a buffer solution (pH 50) with D-GN, the solubility response of D-GN to change in temperature was more sensitive than that in the buffer solution without NaCl In addition, the temperature causing half of the maximum turbidity decreased by about 23°C whenever the NaCl concentration of the buffer solution was increased by 1% D-GN was used successively for repeated hydrolysis reaction of soluble starch, in which D-GN was insolubilized not only by elevating the temperature of reaction mixture with 1% NaCl from 30°C to 38°C, but also by adjusting the NaCl concentration of reaction mixture to 4% at 30°C, followed by its batchwise recovery from a reaction product by centrifugation

Reversed micelles of polymeric surfactants in nonpolar organic solvents. A new microheterogeneous medium for enzymatic reactions.

Abstract: A new microheterogeneous non-aqueous medium for enzymatic reactions, based on reversed micelles of a polymeric surfactant, was suggested. The surfactant termed CEPEI, was synthesized by successive alkylation of poly(ethy1eneimine) with cetyl bromide and ethyl bromide and was found to be able to solubilize considerable amounts of water in benzeneln-butanol mixtures. The hydrodynamic radius of polymeric-reversed micelles was estimated to be in the range 22 - 51 nm, depending on the water content of the system, as determined by means of the quasi-elastic laser-light scattering. Polymeric reversed micelles were capable of solubilizing enzymes (a-chymotrypsin and laccase) in nonpolar solvents with retention of catalytic activity. Due to the strong buffering properties of CEPEI over a wide pH range, it could maintain any adjusted pH inside hydrated reversed micelles. It was found that catalytic behavior of enzymes entrapped in polymeric reversed micelles was rather insensitive to the pH of the buffer solution introduced into the system as an aqueous component, but determined mostly by acid-base properties of the polymeric surfactant itself. Both catalytic activity and stability of entrapped a-chymotrypsin and laccase were found to increase with increasing water content of the system. Under certain conditions, the entrapment of a-chymotrypsin into CEPEI reversed micelles resulted in a considerable increase in catalytic activity and stability as compared to aqueous solution. CEPEI reversed micelles were demonstrated to be promising enzyme carriers for use in membrane reactors. Owing to the large dimensions of CEPEI reversed micelles, they are effectively kept back by a semipermeable membrane, thus allowing an easy separation of the reaction product and convenient recovery of the enzyme.

Buffer effects on aqueous swelling kinetics of polyelectrolyte gels

Abstract: Electrolytes are often added to a gel-swelling medium under the assumption that the important conditions which characterize swelling rates are the solution pH and ionic strength, with little emphasis on the nature of the electrolyte. Previous research by Siegel et al. has indicated that the presence of the un-ionized acidic form of an electrolyte buffer is a primary rate determinant for swelling of a polybase gel. A systematic swelling study on two separate gels, 2-hydroxyethyl methacrylate copolymerized with methacrylic acid (HEMA/MAA) and N,N-dimethylaminoethyl methacrylate (HEMA/DMA), has been performed to investigate the influence of the concentration of the un-ionized buffer by three principal factors: (1) total buffer concentration, (2) solution pH, and (3) buffer pKa. Swelling and deswelling kinetics were obtained. In the presence of an electrolyte buffer, a dramatic swelling rate increase is observed for the HEMA gels, with substantial gains in rate obtained as total buffer concentration rises. Results also emphasize that to enhance swelling kinetics, the pH must be such that the buffer is essentially un-ionized.

Method of stabilizing a carbon dioxide sensor

Abstract: The method of stabilizing a carbon dioxide sensor involves formulation of a bicarbonate buffer solution in the sensor with a bicarbonate ion concentration of from about 30 mM to about 200mM bicarbonate, and preferably about 100 mM bicarbonate. The method also involves treatment of the sensor to reduce the instability that may occur in carbon dioxide sensors when such sensors are exposed to either very low or very high carbon dioxide levels for extended periods of time. The sensor is treated by exposing the sensor to an aqueous solution containing at least 2 weight percent carbon dioxide, for from several days to several months. The solution may be prepared in advance, or may be dynamically infused with carbon dioxide to provide the desired carbon dioxide content.

Compositional Influence on the pH of Reduced‐Moisture Solutions

Abstract: The pH of reduced-moisture systems is not the same as in hydrated systems. As aqueous phosphate buffer solutions become concentrated, the pH of the system decreases. The pH of citrate buffer solutions decreases, then increases as the concentration increases. Identical buffer solutions whose water activity is reduced by the addition of nonionic solutes indicate no correlation of pH with either the water activity reduction or the change in dielectric constant. The response of pH to added solutes appears to be dependent on the chemical nature of the solute and its interaction with water. This study also confirmed the limitations of several theoretical models of ionic activities.

Kinetics and mechanism of isomerization of cyclosporin A.

Abstract: The kinetics of isomerization of cyclosporin A to isocyclosporin A were studied in various nonaqueous solvents as a function of temperature and added methanesulfonic acid. The rate of isomerization was found to be acid-catalyzed over the acid concentration range studied. The choice of organic solvent significantly altered the rate of isomerization. For a series of alcohols, the rate was enhanced with increasing dielectric constant of the media, however, this correlation did not hold upon introduction of the dipolar aprotic solvent, tetrahydrofuran. Conversion of cyclosporin A to isocyclosporin A in tetrahydrofuran was found to contain diminished side reactions as compared to alcoholic solvents. The rate of conversion of isocyclosporin A to cyclosporin A was determined in aqueous buffers as a function of pH, buffer concentration, and temperature. The rates of conversion were extremely rapid compared to the forward reaction. Based on the pH dependencies of dilute solution reactivities, isocyclosporin A displayed a kinetically generated pKa value of 6.9 for the secondary amine moiety. From pH 8 to pH 10 the pH–rate profile plot is linear, with a slope approximately equal to unity, indicating apparent hydroxide ion catalysis. The break in pH–rate profile suggests a change in the rate-determining step upon protonation of isocyclosporin A. The rate of isomerization in plasma was comparable with that found in a pH 7.4 buffer solution, indicating that plasma proteins do not significantly alter the isomerization kinetics of isocyclosporin A to cyclosporin A.

The concentration dependence of adsorption from a mixture of β-lactoglobulin and sodium dodecyl sulfate onto methylated silica surfaces

Abstract: The adsorption from a mixture of SDS and β-Lactoglobulin, 1:5 (), onto a methylated silica surface was studied in situ by ellipsometry. The amounts adsorbed from different concentrations of the mixture, at pH 7, were compared with those adsorbed from the corresponding pure SDS and β-lactoglobulin solutions. At high concentrations of the mixture, where the CMC of SDS is approached or exceeded, the adsorbate was probably dominated by SDS, indicated by similar kinetics and amounts adsorbed as for SDS solution alone. The amount adsorbed increased, in this concentration range, when the system was rinsed with buffer solution. This was probably due to an exchange between SDS and β-lactoglobulin when the system was diluted. At intermediate concentrations of SDS and β-lactoglobulin, the amounts adsorbed from the mixtures increased and reached a maximum. This maximum was observed both before and after rinsing. Before rinsing the adsorbate might have been a mixture of SDS and β-lactoglobulin while after rinsing probably only β-lactoglobulin remained. At low concentrations, larger amounts were adsorbed from the mixture than from β-lactoglobulin solution alone. In this concentration range rinsing caused minor desorption, indicating that SDS is co-adsorbed with the protein, even in those cases were no adsorption from a pure SDS solution was seen. This indicated that the binding of SDS to β-lactoglobulin at low concentrations is stronger than to the silica surface and that this binding facilitated the adsorption of protein. (Less)

Phosphate dialytic removal: enhancement of phosphate cellular clearance by biofiltration (with acetate-free buffer dialysate).

Abstract: Phosphate dialytic removal (PDR) depends in part on the type (acetate or bicarbonate) and the concentration of the buffer dialysate. Plasma phosphate reduction or PDR during a dialysis treatment is th

Interaction between 2-(1-naphthyl)acetic acid and micelles of nonionic surfactants in aqueous solution

Abstract: The interaction of 2-(1-naphthyl)acetic acid (NAA) with nonionic octylphenoxypoly(ethoxy)ethanol (Triton X) and linear primary alcohol (C9-11) poly(ethoxy)ethanol (Neodol 91) surfactants was followed in an aqueous system by UV and fluorescence spectroscopy. There was a distinct shift of the UV absorption maximum to a longer wavelength at surfactant concentrations above the critical micelle concentration (cmc), indicating an intermolecular interaction between NAA and surfactant micelles. Both surfactant concentration and system pH had significant effects. NAA-surfactant interaction occurred only at surfactant concentrations above the cmc where micelles were present and the interaction was favored when the NAA molecule was in the nondissociated form (pH 3.2, pKa = 4.2). Equilibrium constants (K) for the NAA-micelle complex of the Triton X surfactants against buffer solution ranged from 80 to 1161, and log K was inversely related to the log of the number of oxyethylene units in the poly(oxyethylene) chain.

Reactive extraction of cephalosporin c

Abstract: The decomposition rate of cephalosporin C was measured in order to determine the stable operating conditions for extraction, and the same pH dependence as those reported in the past works was obtained. The physical extraction of cephalosporin C with butyl acetate did not occur since it was amphoteric and the fraction of undissociated form was very low.The reactive extraction and strippting of cephalosporin C were studied by using various extractants and buffer solutions. The reactive extraction occurred when tri-n-octylmethylammonium chloride and carbonate buffer were used as an extractant and buffer, respectively. This was the first example of cephalosporin extraction. Cephalosporin C extracted into organic phase was stripped by acetate buffer solution. In the stripping, the anion exchange reaction between cephalosporin C and acetate occurred.