Showing papers on "Buffer solution published in 1988"
TL;DR: In this article, an enzyme microsensor for glucose was fabricated by the electrochemical polymerization method, where a glucose oxidase-entrapped polyaniline film was deposited on the top of a platinum fibre (50 μm in diameter) by electrochemical oxidative polymerization of aniline in a pH 7 buffer solution.
213 citations
80 citations
01 Sep 1988
TL;DR: In this article, a laser Doppler apparatus equipped with narrowly gapped platinized platinum electrodes was used to study the electric properties of bitumen-in-water and Moutray conventional crude-inwater emulsions over a wide range of NaCl concentrations and pH.
Abstract: A laser Doppler apparatus equipped with narrowly gapped platinized platinum electrodes was used to study the electric properties of bitumen-in-water and Moutray conventional crude-in-water emulsions over a wide range of NaCl concentrations and pH. It was found that a dilute buffer solution had to be used to prevent pH drift from occurring on the electrode surfaces. Analysis of the measured mobility using the Ionizable Surface-Group model (K. Takamura and R. S. Chow, Colloids and Surfaces 15, 35 (1985)) revealed that the negative charges of both emulsions were due to the dissociation of carboxylic acids, though Moutray crude oil had only a quarter of the acid groups that existed on the bitumen surfaces. Experiments were also conducted in the presence of Ca2+ and Mg2+. The measured mobilities for both emulsions were again adequately explained by the model when the ion-binding of the cations with the acid groups was included. Several mobilities measured under the presence of the strong electrophoretic relaxation (10−4 M NaCl and CaCl2) exceeded theoretical maximum values predicted by O'Brien and White's computer solution (R. W. O'Brien and L. J. White, J. Chem. Soc., Faraday Trans. 2 74, 1607 (1978)), thus suggesting that their theory might overestimate the relaxation effect.
56 citations
TL;DR: It is shown that the amino acid reduction peak is due toCu(I) reduction of the adsorbed Cu(I)-cysteinate complex; this complex is formed with Cu (I) generated from dissolved copper(II) at the electrode surface at −0.15 V in the presence of cysteine.
56 citations
52 citations
TL;DR: The addition of tertiary amines, such as triethyl amine, markedly increased the peptide yield, probably due to the increase in the concentration of the nucleophilic amine components by neutralization of hydrohalides of amino acid amides.
47 citations
TL;DR: A mass transfer model was developed to describe the dissolution and reaction of an acidic drug, naproxen, from a rotating disk in buffered solutions, and the capacity to make accurate a priori predictions without fitting film thicknesses or diffusion coefficients was found.
34 citations
TL;DR: In this article, the esterification of N-acetyl- l -tryptophan and N- acetyl l -tyrosine was studied using α-chymotrypsin as a catalyst in various hydrophilic organic solvents.
32 citations
TL;DR: It is suggested that both Na+/H+ and HCO3−/Cl− exchange transport mechanisms are taking roles in the intracellular pH regulation in the lacrimal gland acinar cells.
Abstract: Intracellular pH (pH
i
) of the acinar cells of the isolated, superfused mouse lacrimal gland has been measured using pH-sensitive microelectrodes. Under nonstimulated condition pH
i
was 7.25, which was about 0.5 unit higher than the equilibrium pH. Alterations of the external pH by ±0.4 unit shifted pH
i
only by ±0.08 unit. The intracellular buffering value determined by applications of 25mm NH
4
+
and bicarbonate buffer solution gassed with 5% CO2/95% O2 was 26 and 46mm/pH, respectively Stimulation with 1 μm acetylcholine (ACh) caused a transient, small decrease and then a sustained increase in pH
i
. In the presence of amiloride (0.1mm) or the absence of Na+, application of ACh caused a significant decrease in pH
i
and removal of amiloride or replacement with Na+-containing saline, respectively, rapidly increased the pH
i
. Pretreatment with DIDS (0.2mm) did not change the pH
i
of the nonstimulated conditions; however, it significantly enhanced the increase in pH
i
induced by ACh. The present results showed that (i) there is an active acid extrusion mechanism that is stimulated by ACh; (ii) stimulation with ACh enhances the rate of acid production in the acinar cells; and (iii) the acid extrusion mechanism is inhibited by amiloride addition to and Na+ removal from the bath solution. We suggest that both Na+/H+ and HCO
3
−
/Cl− exchange transport mechanisms are taking roles in the intracellular pH regulation in the lacrimal gland acinar cells.
25 citations
TL;DR: In this article, a local-equilibrium chromatographic model is outlined to describe the concentration velocities for injection of alkaline buffers into a linear porous medium that exhibits reversible sodium/hydrogen exchange.
Abstract: Use of relatively low-pH alkaline buffers, such as sodium carbonate or sodium silicate, is explored as a means for overcoming sodium/hydrogen ion-exchange delay in alkaline waterflooding. A local-equilibrium chromatographic model is outlined to describe the concentration velocities for injection of alkaline buffers into a linear porous medium that exhibits reversible sodium/hydrogen exchange. The theory predicts a buffer ion-exchange wave that is substantially faster than that for equivalent-pH sodium hydroxide solutions. New experimental displacement data are presented for NaOH over a pH range from 11 to 13 and for 0.1, 0.5, and 1.0 wt% Na/sub 2/CO/sub 3/ flowing through a 1 wt% NaCl brine saturated Berea sandstone core at 50/sup 0/C (122/sup 0/F). To permit a complete description of the system, column effluent concentrations are measured for sodium ions, hydroxide ions, H/sup 3/-tagged water, and /sup 14/C-tagged carbonate. The experiments confirm that Na/sub 2/CO/sub 3/ propagates through the Berea sand at a higher rate than NaOH. For example, at pH=11.4, Na/sub 2/CO/sub 3/ migrates with a velocity that is 3.5 times faster than NaOH. Comparison of experiment with the ion-exchange chromatography theory shows good agreement. The authors successfully model the concentration histories of tritium-labeled water, total carbon, sodium, and hydroxide, allmore » with no adjustable parameters. This work establishes with both theory and experiment that buffered alkali significantly increases the propagation speed of hydroxide in reservoir sands in comparison with unbuffered alkali at equivalent sodium and hydroxide concentrations. Because lower-pH buffered alkali can also protect against rock dissolution loss, the validated reduction of buffer ion-exchange lag considerably improves the promise of the alkaline flooding process for field application.« less
23 citations
TL;DR: In this paper, a pH 16 maleic acid buffer system was incorporated in the reaction medium before the addition of reagents to improve the performance of the EB method, which has a greatly improved precision (17% compared with 6% for ten samples containing 65 µg of S with absorbances ranging from 0387 to 0412).
Abstract: The Ethylene Blue (EB) method, used in the determination of H2S in various environments, has given cause for concern due to poor precision and varying sensitivity The reason for this has been shown to be poor pH control in the solution at the time of reaction Both the rate of formation of the blue colour and the final absorbance obtained are affected by the amount of sulphuric acid added with the reagent (p-diethylaminoaniline) Good precision can be attained if the volumes of reagents added are strictly controlled, but the method has been improved further by incorporating a pH 16 maleic acid buffer system in the reaction medium before the addition of reagents The new method is tolerant to wide variations in the amounts and concentrations of absorbent and reagents and has a greatly improved precision (RSD = 17% compared with 6% for ten samples containing 65 µg of S with absorbances ranging from 0387 to 0412) Extraction of the EB into 10 ml of chloroform can improve the precision further (RSD = 0643% for ten samples containing 62 µg of S with absorbances ranging from 0549 to 0557)
TL;DR: In this paper, a very sensitive and rapid potentiometric determination of trace chlorine in water is described, based on the transient potential changes which appears during the reduction of dissolved chlorin with an iron(III)/iron(II) potential buffer containing chloride and sulfuric acid.
TL;DR: In this article, a membrane reactor was used for triglyceride hydrolysis in low temperature and applied pressure, where the enzyme lipase was dynamically immobilized on the pressurized face of the ultrafiltration membranes.
TL;DR: The results showed that whereas the self-association process was found for 1,8-dihydroxyanthraquinone alone, the monomeric form is microincluded in beta- and gamma-cyclodextrins, the interaction is more favored as the cavity size of cyclodextRins is larger, the molecule being more tightly bound with gamma- than with beta-cyclodesxtrin.
TL;DR: In this article, the adsorption of β-cyclodextrin (β-CD) on a dropping mercury electrode has been studied in Na 2 SO 4 and phosphate buffer solutions by drop time measurements.
TL;DR: The passivation and depassivation of pure iron in carbonateibicarbonate buffer at pH 9.2 shows features that are not found in borate buffers.
TL;DR: The second-order rate constant for base-catalysed cyclization reaction is (4.06 ± 0.05)× 104 l mol 1 s−1 s −1.84 at 30 °C.
Abstract: The cyclization of ethyl N-[o-(N-hydroxycarbamoyl)benzoyl]carbamate (SH) to N-hydroxyphthalimide (NHPH) has been studied within the pH range 5.18–7.84 at 30 °C. The observed first-order rate constants are linearly dependent on [–OH]. Buffer catalysis could not be detected and the value of the second-order rate constant, kOH, for the specific base-catalysed cyclization reaction is (4.06 ± 0.05)× 104 l mol–1 s–1. The magnitude of kOH is ca. 3 × 105-fold greater than kOH for hydroxide ion-catalysed hydrolysis of methyl benzoate. The suggested mechanism involves the preequilibrium formation of the anionic substrate which cyclizes to produce anionic tetrahedral intermediate followed by its breakdown as the rate-determining step. The cyclized product, NHPH, reacts rapidly and reversibly with hydroxylamine to produce o-(N-hydroxycarbamoyl)benzohydroxamic acid (P). The equilibrium constants for the processes NHPH + NH2OH ⇌ P and PH + H++ NH2OH ⇌ P, where PH is the ionized NHPH, calculated at different pH using authentic NHPH, reveal a non-linear dependence on total hydroxylamine buffer concentrations.
TL;DR: The results suggest that the increase in pH mainly increases the transport of HgCl2 as a result of the conversion to hydroxide forms of HG such as Hg(OH)Cl and Hg (OH)2, and Cl- Br- and I- act as the competing ions with OH- and decrease the transportof Hg.
Abstract: Composite effects of pH and halide ions on the transport of HgCl2 into brush border membrane vesicles (BBMV) were investigated in rats. BBMV were incubated for 10 min. in buffer solution at different pH containing 10−4 M HgCl2. The increase in pH increased the uptake of Hg by BBMV as a result of the increase in transport of Hg into intravesicular space and decrease in binding of Hg to BBMV. The isotonic displacement of NaCl in the buffer solution by LiCl or KCl did not change the uptake of Hg at each pH. The displacement of NaCl by mannitol increased the uptake of Hg at each pH, while the displacement by NaBr or Nal decreased the uptake and diminished the increasing effect of pH on the uptake of Hg. These changes in uptake of Hg due to the displacement were mainly ascribed to the changes in transport of Hg. These results suggest that the increase in pH mainly increases the transport of HgCl2 as a result of the conversion to hydroxide forms of Hg such as Hg(OH)Cl and Hg(OH)2, and Cl−, Br− and I− act as the competing ions with OH− and decrease the transport of Hg.
TL;DR: In this article, the electrochemistry of galena in an acetate solution at pH 4.6 has been studied through the use of linear sweep voltammetry, and the voltammograms for anodic limits as high as 845 mV indicate that S0 is the sulphur-bearing species generated during the oxidative dissolution of Galena.
Abstract: The electrochemistry of galena in an acetate solution at pH 4.6 has been studied through the use of linear sweep voltammetry. Analysis of the voltammograms for anodic limits as high as 845 mV indicates that S0 is the sulphur-bearing species generated during the oxidative dissolution of galena. Furthermore, interpretation of the electrochemical data on the basis of thermodynamic considerations indicates that galena interacts with the acetate electrolyte and that Pb(CH3COO)2(aq) is also produced during anodic oxidation. When the scan direction is reversed in the cathodic direction, the oxidation products are removed by two reduction reactions when the solution is quiescent: the recombination of Pb(CH3COO)2 and S0 to form PbS and the reduction of S0 to H2S. In a stirred solution, only the second reaction is possible. Experiments conducted in the presence of 10−3 or 10−2 M lead acetate indicate that the presence of dissolved lead tends to inhibit the dissolution process. Furthermore, metallic lead can begin to deposit on the galena surface when the potential drops below about −330 mV SHE. The data also agree most closely with thermodynamics when Pb(CH3COO)2 is considered to be the aqueous species involved in the deposition and dissolution of metallic lead.
TL;DR: The extent to which this reaction was dependent on viscosity was found to be constant, within experimental error, over the entire range of MES buffer concentrations studied (1-20 mM) and was qualitatively and quantitatively the same when an exceptionally large buffer was used instead of the more commonly used biological buffer.
Abstract: In our earlier paper we showed that the rates of CO2 hydration and HCO3- dehydration catalyzed by the high-activity form of mammalian erythrocyte carbonic anhydrase (CA II) were dependent on solution viscosity increase and that the effect was linked to some kind of proton-transfer-related event [Pocker, Y., & Janjic, N. (1987) Biochemistry 26, 2597-2606]. In order to further elucidate the source of the observed viscosity effect, the dependence of kcat and Km for CA II catalyzed HCO3- dehydration at pH 5.90 on sucrose-induced viscosity increase was investigated at several concentrations of 2-(N-morpholino)ethanesulfonic acid (MES) buffer, including the very low buffer concentration region (less than 10 mM) where the proton transfer between the shuttle group on the enzyme and buffer becomes rate limiting. In all examined cases, kcat steadily decreased with added sucrose while Km remained independent of the viscosity increase. The extent to which this reaction was dependent on viscosity was found to be constant, within experimental error, over the entire range of MES buffer concentrations studied (1-20 mM). Furthermore, the viscosity effect was qualitatively and quantitatively the same when an exceptionally large buffer (i.e., bovine serum albumin) was used instead of the more commonly used biological buffer (i.e., MES).(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: There seems to be no alternative, for a well behaved IEF system, to the random synthesis of carrier ampholytes (CA), as epitomized by the classical Vesterberg approach, and the only valid alternative to conventional CA-IEF, and much superior, is the revolutionary methodology of immobilized pH gradients.
TL;DR: The method was accurate and sensitive for the analysis of PAM-2Cl in water and tablets and Beer's law was obeyed at concentrations up to 60 microM.
TL;DR: In this paper, the amperometric carbon dioxide sensor uses chemoautotrophic thermophilic bacteria and an oxygen-sensing electrode, which was fabricated by packing the sensitive area of the bicarbonate sensor in a cell with a gas-permeable membrane on one side.
Abstract: The amperometric carbon dioxide sensor we developed uses chemoautotrophic thermophilic bacteria and an oxygen-sensing electrode. The sensor was fabricated by packing the sensitive area of the bicarbonate sensor in a cell with a gas-permeable membrane on one side. The membrane was constantly supplied with an oxygen-saturated buffer solution. The sensor's operating range was 34°C to 58°C. A linear relationship was obtained in a 1-mM to 8-mM NaHCO3 concentration in a buffer solution (pH 5.5) and a 3% to 12% CO2 concentration in air. The effect of the sensor's low sensitivity to sodium acetate and ethanol was greatly improved by supplying fresh, oxygen-saturated buffer solution. The sensor had a life of more than a month.
TL;DR: Adsorptive voltammetry with the catalytic hydrogen wave could provide a sensitive method for determining trace amounts of lipoic acid and lipoamide.
TL;DR: In this paper, the cyclic and rotating-disk voltammetric studies showed that the semiquinone radical intermediate is an active species m the catalytic reduction, and the theoretical treatment newly developed gave support to this mechanism.
TL;DR: In this article, the anodic oxidation of UO2 was studied in aqueous phosphate solutions over the pH range 4 to 11, using a combination of electrochemical and X-ray photoelectron spectroscopic techniques.
Abstract: The anodic oxidation of UO2 has been studied in aqueous phosphate solutions over the pH range 4 to 11, using a combination of electrochemical and X-ray photoelectron spectroscopic techniques. The e...