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Showing papers on "Buffer solution published in 1993"


Journal ArticleDOI
TL;DR: Potentiometric pH selective tips for scanning electrochemical microscopy (SECM) have been developed and used to image local pH changes in a variety of model chemical systems as discussed by the authors, and a simple method for fabricating antimony microdisk electrodes suitable for use in SECM is described.
Abstract: Potentiometric pH selective tips for scanning electrochemical microscopy (SECM) have been developed and used to image local pH changes in a variety of model chemical systems. Images of pH profiles around a platinum microelectrode during water reduction, a corroding disk of silver iodide in aqueous potassium cyanide, a disk of immobilized urease hydrolyzing urea, and a disk of immobilized yeast cells in glucose solution were obtained. A simple method for fabricating antimony microdisk electrodes suitable for use in SECM is described. The general theory for SECM with potentiometric ion selective tips is also present, assuming that the tip is a purely passive sensor

185 citations


01 Jan 1993
TL;DR: In this article, the pH values of conjugate acid-base pairs of 2-aminopyridine, 2-amino-2-hydroxymethyl-1,3-propanediol (tris), tetrahydro-1-4-isoxazine (morpholine), and 2amino 2-methyl-1-, 3-propanediol (bis) were re-evaluated to assign pH values based on the total hydrogen ion concentration scale to equimolal buffer solutions based on these compounds.
Abstract: Published e.m.f. values measured using the cell ... (formule)... where p° = 101.325 kPa, and BH + and B are the conjugate acid-base pairs of 2-aminopyridine, 2-amino-2-hydroxymethyl-1,3-propanediol (tris), tetrahydro-1,4-isoxazine (morpholine), and 2-amino-2-methyl-1,3-propanediol (bis), have been re-evaluated to assign pH values based on the «total» hydrogen ion concentration scale to equimolal (m = 0.04 mol kg −1 ) buffer solutions based on these compounds.

176 citations


Journal ArticleDOI
TL;DR: In this article, the electrochemical oxidation of hydrogen peroxide on Pt disk and Pt + Ir wire electrodes was studied in physiological buffer at pH 7.40 in order to establish a practical protocol for H 2 O 2 -based biosensors.

160 citations


Journal ArticleDOI
TL;DR: Theoretical and experimental results indicate the largest range of effective electroosmotic flow control via an applied radial voltage occurs at low ph, while at high buffer pH the relationship appears to be linear and is only over a limited range of flow velocities.
Abstract: Electroosmotic flow has been shown to be controlled via an applied radial voltage. Many factors determine the effectiveness of this control, and one major factor is buffer pH. In this study the effectiveness of the applied radial voltage for controlling electroosmotic flow while varying buffer pH is examined. Previously developed theory is applied and compared to experimental results for a pH range from 1.4 to 6.32. Analysis time is dramatically reduced by applying a radial voltage for separation of a peptide mixture at pH 1.4. Theory predicts laminar flow profiles under some conditions when applying this technique. However, experimental evidence at pH 6.32 and 1.4 shows no evidence of band broadening from a laminar flow profile. Theoretical and experimental results indicate the largest range of effective electroosmotic flow control via an applied radial voltage occurs at low ph. Furthermore, a sigmoidal relationship between electroosmotic flow and applied radial voltage is clearly apparent under these conditions. In contrast, at high buffer pH ( > 6) the relationship appears to be linear and is only over a limited range of flow velocities.

106 citations


Journal ArticleDOI
TL;DR: Good separations of restriction fragments could be achieved with solutions of PAA or HEC as separation media after surface pretreatment of fused silica capillaries by either PVA rinsing or coating according to Hjertén [41].
Abstract: Separation of DNA restriction fragments in dilute buffer solutions of network forming polymers such as linear polyacrylamide (PAA), hydroxyethyl cellulose (HEC) and polyvinylalcohol (PVA) in phosphate buffer were investigated. PVA in buffers already became inhomogeneous after a few separations with resultant deterioration of resolution. Hydroxylic polymers, capable of forming suitable networks in buffers, are strongly adsorbed to fused silica surfaces suppressing the electroosmotic flow. These polymers could be applied as surface modifiers in capillaries, filled with buffer media containing other polymers such as PAA: Suppression of the electroosmotic flow by adsorbed HEC at pH 7 was slightly more effective than with PVA but the former coating was less stable due to weaker binding to the fused silica surface. Good separations of restriction fragments could be achieved with solutions of PAA or HEC as separation media after surface pretreatment of fused silica capillaries by either PVA rinsing or coating according to Hjerten [41].

101 citations


Journal ArticleDOI
TL;DR: In this article, scanning force microscopy (SFM) images of lipid membranes at -25°C were compared with those at room temperature both in air and in glycerol/buffer solution.

99 citations


Journal ArticleDOI
TL;DR: Findings indicate that the neutral to basic transition is important for the calcium-binding properties of albumin, which is a reversible, gradual conformational change of the protein at pH 6-9.
Abstract: We examined the suitability of nine organic buffers for studying calcium binding to albumin by equilibrium dialysis. Results obtained with defatted human serum albumin showed that 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and 2-([tris(hydroxymethyl)methyl] amino)ethanesulfonic acid were superior. Scatchard analysis of the experimental data from an extensive study performed in HEPES at pH 7.4 and 20 degrees C revealed (putting n(i) = 1, i = 1-4) k1 = 367 L/mol, k2 = 314 L/mol, k3 = 291 L/mol, and k4 = 179 L/mol. The very weak binding was characterized as n5 = 10 and k5 = 40 L/mol. The results were also analyzed in terms of stoichiometric association constants. The constants K1 and K2 were calculated to be 1513 and 647 L/mol, respectively, whereas the other constants were considered undeterminable. pH studies showed that in the interval 6.8-7.4, binding was not influenced by changes in acidity. Increasing pH to above the physiological value resulted in increased binding. At pH 8.0, k1 was increased almost fourfold, whereas k2 and k3 were approximately doubled. These findings indicate that the neutral to basic transition is important for the calcium-binding properties of albumin. The transition is a reversible, gradual conformational change of the protein at pH 6-9.

68 citations


Journal ArticleDOI
TL;DR: Capillary electrophoresis for the determination of inorganic metal cations in the presence of various complexing agents was investigated in this paper, where acetic, glycolic, lactic, hydroxyisobutyric, oxalic, malonic, malic, tartaric, succinic and citric acid.

63 citations


Journal ArticleDOI
TL;DR: The difference between experimental and theoretical pH profiles is due to the inconsistency of the generally accepted model of the "unstirred layer", assuming the existence of a strict boundary between the regions of "pure diffusion" and "ideal stirring".

57 citations


Journal ArticleDOI
TL;DR: In this article, a cyclic reaction between catechol and 1,2-benzoquinone takes place by combining the tyrosinase reaction and the chemical reduction of 1 2 -benzo-quinone to Catechol by l -ascorbic acid.

56 citations


Journal ArticleDOI
TL;DR: A method for determining the p K a values of substituted phenols based on anodic voltammetry has been validated and applied to various cases as mentioned in this paper, where the dependence of the electrochemical oxidation potentials of phenols on the solution pH is investigated.

Journal ArticleDOI
TL;DR: The hypothesis that BAPTA-type buffers exert their effect by shuttling calcium from regions of high concentration to those of lower concentration, reducing any calcium concentration gradients present in the Xenopus embryo is supported.
Abstract: Microinjection of calcium buffers into the two-cell Xenopus laevis embryo delays cell division in a dose-dependent manner. Four calcium buffers in the BAPTA series with different affinities for calcium were used to distinguish between a localized calcium gradient regulating cleavage and the global calcium concentration regulating this event. DibromoBAPTA (Kd = 1.5 microM) was found to delay cleavage at the lowest intracellular concentration (1.3 mM) of the four buffers tested. The effectiveness of the calcium buffers was dependent upon the buffer dissociation constant but not in a linear fashion. The concentration of buffer required to delay cleavage increased as the buffer's dissociation constant shifted above or below that of the optimum buffer, dibromoBAPTA. This relationship between a calcium buffer's effectiveness at delaying cleavage and its calcium affinity provides support for the hypothesis that a calcium concentration gradient is required for normal cell cycle progression (Speksnijder, J. E., A. L. Miller, M. H. Weisenseel, T.-H. Chen, and L. F. Jaffe. 1989. Proc. Natl. Acad. Sci. USA. 86:6607-6611). DibromoBAPTA was also injected with two different amounts of coinjected calcium to test the possibility that the free calcium concentration of the buffer solution is the important parameter for delaying cleavage. However, we found that changes in buffer concentration have a much stronger effect than changes in the free calcium concentration. This observation supports the hypothesis that BAPTA-type buffers exert their effect by shuttling calcium from regions of high concentration to those of lower concentration, reducing any calcium concentration gradients present in the Xenopus embryo.

Journal ArticleDOI
TL;DR: In this article, Nafion membranes were deposited on the top of the glucose ENFETs by a spin-coating procedure, which resulted in a substantial reduction of the effect of the buffer concentration on the EN-FET's response and in an extension of the dynamic range of the sensor up to concentrations of more than 10 mM glucose.

Patent
18 May 1993
TL;DR: In this article, a method for producing a thermally shock resistant washcoated substrate involves introducing a buffer solution into the microcracks, and optionally the micropores of a porous sintered body, the pH of buffer solution being at a predetermined value to result in the formation of a gel on contact of the buffer solution with the slurry which is to be subsequently applied, contacting the body with a washcoating slurry to form a gel at the interface of buffer and slurry.
Abstract: A method for producing a thermally shock resistant washcoated substrate involves introducing a buffer solution into the microcracks, and optionally the micropores of a porous sintered body, the pH of the buffer solution being at a predetermined value to result in the formation of a gel on contact of the buffer solution with the slurry which is to be subsequently applied, contacting the body with a washcoating slurry to form a gel at the interface of the buffer solution and slurry. Formation of the gel prevents the slurry from entering the microcracks. The body is then calcined at a temperature and for a time sufficient to form the washcoated substrate.

Journal ArticleDOI
TL;DR: Nafion-coated glassy carbon electrodes containing the copper(II) complex prepared from the tripodal tris(pyrazol-1-ylmethyl)amine ligand are shown to effectively mediate electron transfer to cytochrome c and the copper-containing enzyme tyrosinase.
Abstract: Nafion-coated glassy carbon electrodes containing the copper(II) complex prepared from the tripodal tris(pyrazol-1-ylmethyl)amine ligand are shown to effectively mediate electron transfer to cytochrome c and the copper-containing enzyme tyrosinase. For both species, a concentration-dependent increase in cathodic current is observed at the peak potential for the mediator following addition of protein to the buffer solution containing the modified electrode. The average increase for a cytochrome c concentration of 0.19 mM is 11±3.2%, while that for 5.6 μM tyrosinase is 9.5±4.6%

Journal ArticleDOI
TL;DR: A poly(thionine)-modified basalplane pyrolytic graphite electrode, which can be prepared by a potential-sweep electrolysis of the corresponding monomer in acetonitrile media, shows an excellent electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 6.9), with an activation overpotential which is ca. 400 mV lower than that of the bare electrode.
Abstract: A poly(thionine)-modified basal-plane pyrolytic graphite electrode, which can be prepared by a potential-sweep electrolysis of the corresponding monomer in acetonitrile media, shows an excellent electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 6.9), with an activation overpotential which is ca. 400 mV lower than that of the bare electrode.

Journal ArticleDOI
TL;DR: Preliminary results, using an excimer laser operated at 248 nm, show that the fluorescence intensity of isonicotinic acid is substantially enhanced with the addition of 0.3% hydrogen peroxide to the phosphate buffer system.

Journal ArticleDOI
TL;DR: It is proposed that inactivation of β-galactosidase is due to formation of thermally denatured (unfolded) protein, which aggregates dependent on the water:protein ratio, either via noncovalent interactions at a high water: proteins ratio in solution or via covalent interaction at a low water: protein ratio in the freeze-dried state.
Abstract: Aggregates formed during storage of freeze-dried β-galactosidase were compared with those formed in solutions. Freeze-dried β-galactosidase aggregated during storage in the presence of moisture, producing a protein precipitate which was soluble in guanidine hydrochloride solution but not in buffer solution. The protein precipitate dissolved in guanidine solution exhibited a large molecular size by high-performance size exclusion chromatography and converted to proteins of original size in the presence of dithiothreitol. It is suggested that the aggregation involves chemical interaction via covalent disulfide bonding. In contrast, β-galactosidase in aqueous solution aggregated without formation of protein precipitates. Soluble aggregates were converted to proteins of original size in guanidine solution without dithiothreitol, suggesting noncovalent bonding. The difference in aggregation behavior may be ascribed to the difference in the water:protein ratio. We propose that inactivation of β-galactosidase is due to formation of thermally denatured (unfolded) protein, which aggregates dependent on the water:protein ratio, either via noncovalent interactions at a high water:protein ratio in solution or via covalent interaction at a low water:protein ratio in the freeze-dried state.

Journal ArticleDOI
TL;DR: Five glass compositions in or near the bioactive region in the system SiO2-Na2O-CaO-P2O5-Al2O3-B2 O3 were studied in vitro by immersion in Tris buffer to estimate the thickness of the Si-rich (Si gel) layer.
Abstract: Five glass compositions in or near the bioactive region in the system SiO2Na2OCaOP2O5Al2O3 were studied in vitro by immersion in Tris buffer. The Si concentration can be taken as a measure of the amount of dissolved glass, whereas the Na concentration can be used to estimate the thickness of the Si-rich (Si gel) layer. Upon immersing a bioactive glass into Tris buffer, a surface layer of a few micrometer thickness is dissolved during the first 8 h. During the first few hours of immersion, the rate of dissolution of the glass network is equal to or exceeds that of the growth of the Si-rich layer. If the glass contains Al2O3, most of the aluminum that would be released due to dissolution of the silica network is enriched in the Si-rich surface layer that forms due to leaching. Al2O3 is not only bonded by the Si gel but also interferes with formation of culcium phosphate. © 1993 John Wiley & Sons, Inc.

Journal ArticleDOI
TL;DR: No significant relationship was found between the elution order and separation and the structure of the beta-blockers in micellar electrokinetic capillary chromatography with an organic modifier in buffer solutions.

Journal ArticleDOI
TL;DR: In this paper, the electrochemical behavior of a redox-active ferrocene-modified siloxane polymer (PBF) which is capable of acting as an electron mediator for flavin enzymes was examined.
Abstract: The electrochemical behavior of a redox-active ferrocene-modified siloxane polymer (PBF) which is capable of acting as an electron mediator for flavin enzymes was examined. By cyclic voltammetry, it was revealed that the redox activity of PSF film was strongly affected by anionic species in the soaking solution. While a highly stable current response corresponding to the ferrocene/ ferricinium (Fc 0 /Fc + ) redox couple of the film was obsersed in NaClO 4 or NaBF 4 supporting electrolyte solutions, the current response gradually decreased by cycling of the potential in an aqueous solution of NaCl, NaNO 3 sodium p-toluenesulfonate, or phosphate buffer

Journal ArticleDOI
TL;DR: In this article, a fused-silica capillary with specially designed charged surface coatings was developed for the control of electroosmotic flow and for the separation of peptides and proteins in capillary electrophoresis.
Abstract: Fused-silica capillaries with specially designed charged surface coatings were developed for the control of electroosmotic flow and for the separation of peptides and proteins in capillary electrophoresis. Cryptand moieties were immobilized onto the capillary surface through a crosslinking reaction of a cryptand-containing polymer and copolymerization of a cryptand-containing monomer. The resultant coatings provided switchable electroosmotic flow from low to high pH due to the complexing ability of the cryptand moieties with the metal ions from the buffer solution. A positively charged quaternary amine surface-coated column was found to be very effective in reversing the electroosmotic flow compared to an untreated fused silica capillary, and to be suitable for separation of proteins whose pI values are greater than the buffer pH. Also, a negatively charged sulfonic acid surface-coated column could be used to stabilize the electroosmotic flow from pH 3 to 9, and the magnitude of the electroosmotic flow could be controlled by varying the concentration of sulfonic acid groups in the coating solution. This negatively charged surface coating gave excellent reproducibility for the separation of a tryptic digest of β-casein.


Journal ArticleDOI
TL;DR: Capillary electrophoresis was applied to effect the separation of Maillard reaction products generated by the reaction of 5-hydroxymethylfurfural (5-HMF) with glycine.

Journal ArticleDOI
TL;DR: In this paper, the dynamic swelling of polymer networks in ionic solution was modelled with a Hamiltonian equation of motion which was transformed into an equation describing the system displacement vector as a function of time.


Journal ArticleDOI
TL;DR: In this paper, a novel technique for the manufacture of water-insoluble film coatings on drug-loaded saccharose pellets is described, which is based on the simultaneous spraying of aqueous solutions of a film-forming polymer and an appropriate crosslinking agent.

Journal ArticleDOI
TL;DR: In this paper, the sweep rate dependence of peak current and peak potential, as well as the form of the wave, were examined on the basis of the Gilman mechanism that the electron transfer from a complex consisting of CO and oxygen containing species is the rate-determining step.
Abstract: The oxidation wave of CO preadsorbed at 50 mV on Pt(1 1 1), (1 0 0) and (1 1 0) electrodes in phosphate buffer solution of pH 3 was observed as a function of the sweep rate. The sweep rate dependence of the peak current and peak potential, as well as the form of the wave, were examined on the basis of the Gilman mechanism that the electron transfer from a complex consisting of CO and oxygen containing species is the rate-determining step. An electron transfer step from CO itself was excluded. The peak current and peak potential analyses and the wave simulation gave the same value for Δf, the change in the interaction energy during the formation of the activated complex from the reactants. Δf was sweep-rate and surface-structure dependent. The nature of Δf was discussed.

Patent
14 Sep 1993
TL;DR: In this article, a protein adsorption inhibitor containing 2- methacryloyloxyethylphosphorylcholine(MPC) polymer and/or copolymer of MPC-containing constituent is used.
Abstract: PURPOSE:To suppress the adsorption of protein to antibody combination solid phase, antigen combination solid phase, or solid phase and then improve analysis accuracy without affecting a measurement system by a specific protein adsorption inhibitor. CONSTITUTION:A protein adsorption inhibitor containing 2- methacryloyloxyethylphosphorylcholine(MPC) polymer and/or copolymer of MPC-containing constituent is used. The applicable range is the analysis method of living thing related substance where enzyme reaction or immunity or the antigen antibody reaction of immunity globulin are generally utilized. The MPC polymer and/or MPC copolymer using the protein adsorption inhibitor are the MPC individual polymer or a copolymer with other vinyl monomers and the NIPC content within the constituent of the polymer A is preferable 1-100mol.% and an average molar weight is preferable 1000-1,000,000. The inhibitor can be used by adding itself to a solvent medium where the polymer A can be dissolved, for example, phosphoric acid buffer solution, acetic buffer solution, and carbon buffer solution.

Journal ArticleDOI
TL;DR: Unless both pH and the buffer composition are taken into account, SPQ is unsuitable for studying the concomitant transmembrane fluxes of Cl- and H+.
Abstract: The fluorescence intensity of 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) in an N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) 2-(N-morpholino)ethanesulfonic acid (MES)-Tris(hydroxymethyl)aminomethane buffer, pH 7.0, decreased as a function of Cl- concentration and/or gluconate concentration, as expected. Contrary to expectation, however, the fluorescence intensity progressively increased as the pH decreased, independently of the presence of gluconate. Consequently, the modulation of SPQ fluorescence by commonly used buffers was investigated as a function of pH. Titration curves demonstrated SPQ quenching and yielded pK values characteristic of each buffer. from here, pH-independent Stern-Volmer constants, KQbase, were calculated for each of the morpholine derivatives, MES and 3-(N-morpholino)-2-hydroxypropanesulfonic acid. In contrast, HEPES and piperazine-N,N'-bis(2-ethanesulfonic acid), which are piperazine derivatives, exhibited an additional pH-independent "molecular" quenching constant KmQ throughout the pH range 3-10. To study chloride fluxes, therefore, what counts is the apparent Cl-Stern-Volmer constant KappCl, which is a function of both pH and buffer composition. Equations describing these relationships are presented. In conclusion, unless both pH and the buffer composition are taken into account, SPQ is unsuitable for studying the concomitant transmembrane fluxes of Cl- and H+.