Showing papers on "Buffer solution published in 2001"

Effect of initial buffer composition on pH changes during far-from-equilibrium freezing of sodium phosphate buffer solutions.

Abstract: Purpose. This study aims to assess the pH changes induced by salt precipitation during far-from-equilibrium freezing of sodium phosphate buffers as a function of buffer composition, under experimental conditions relevant to pharmaceutical applications—sample volumes larger than a few microliters, experiencing large degrees of undercooling and supersaturation.

Stabilized antibody-containing preparations

Abstract: Stabilized preparations containing an antibody in a glycine buffer solution and/or a histidine buffer solution; and a process for producing a stabilized protein-containing preparation characterized in that the pH value is controlled with the use of a basic amino acid, a basic amino acid derivative or a salt thereof.

Electrochemical determination of dopamine using a poly(2-picolinic acid) modified glassy carbon electrode.

Abstract: A poly(2-picolinic acid) chemically modified electrode (CME) for the determination of dopamine (DA) by cyclic voltammetry is described. Compared with a bare glassy carbon electrode, the CME exhibits a 200 mV shift of the oxidation potential of DA in the cathodic direction and a marked enhancement of the current response. In pH 7.0 buffer solution, a linear calibration graph is obtained over the range from 2.5 ×10−7 to 1.0 × 10−5 mol dm−3 with a correlation coefficient of 0.998. The detection limit is 3.0 × 10−8 mol dm−3. The modified electrode eliminated efficiently the interference from ascorbic acid (AA) when present in a 150-fold concentration ratio. It also showed excellent stability and reproducibility.

Stabilization of Gas-Phase Noncovalent Macromolecular Complexes in Electrospray Mass Spectrometry Using Aqueous Triethylammonium Bicarbonate Buffer

Abstract: The use of triethylammonium bicarbonate (TEAB) solution in electrospray mass spectrometry proved to be a very efficient way for studying proteins or noncovalent protein complexes under “nondenaturing” conditions. The low charge states observed in the mass spectra improve the separation of ions arising from macromolecular species of close masses. Moreover, the multiply charged ions generated in a TEAB solution are significantly more stable than those formed under more conventional conditions (for example, with ammonium bicarbonate or acetate solution). The analytical interest of TEAB for the analysis of macromolecular species that can easily dissociate in the gas phase, such as hemoglobin or other macromolecular noncovalent complexes, is demonstrated.

Modelling the effect of pH on the colour degradation of blanched broccoli

Abstract: In ready-to-eat salads, a low pH is often applied in the salad dressing. The effect of pH on the colour change of blanched-frozen-and-thawed broccoli was studied. Different acids were used to achieve the pH values in buffer solutions. A model on chlorophyll degradation in fruits and vegetables was developed based on a simplification of existing knowledge. From integral non-linear regression analysis, it was concluded that the pH gradient at the boundary between product and buffer solution had a marked effect at low pH values. Furthermore, based on the analyses and the obtained residuals, another colour degrading process was revealed that gradually increases in relative importance at higher pH values. The effect of the five acids applied could be attributed to a single proportionality factor, probably related to the hydrophilic nature of the acid applied. The statistical analysis showed a percentage variance accounted for (R2adj) of more than 99.6%. The apparent rate of colour degradation was found to be linearly related to the concentration of hydrogen ions.

Direct electron transfer in the system gold electrode-recombinant horseradish peroxidases

Abstract: The kinetics of the bioelectrocatalytic reduction of hydrogen peroxide has been studied at gold electrodes modified with different forms of horseradish peroxidase (HRP). Native HRP, wild type recombinant HRP (rec-HRP) and its two mutant forms containing a six-histidine tag at the C- or N-terminus, C His rec-HRP and N His rec-HRP, respectively, have been used for an adsorptive modification of the gold electrodes. The histidine sequences, i.e. histidine tags, were introduced into the peroxidase structure by genetic engineering of non-glycosylated rec-HRP using an Escherichia coli expression system. Experiments with a gold rotating disc electrode demonstrated that electrodes with the adsorbed rec-HRP forms exhibited high and stable current response to H 2 O 2 due to its bioelectrocatalytic reduction based on direct (mediatorless) ET between gold and the active site of HRP. The heterogeneous ET rate constants were evaluated to be in the order of 20 or 33 s ' between rec-HRP or its histidine mutants and gold, respectively, in 0.01 M phosphate buffer (pH 7.4) containing 0.15 M NaCl. The increase in the heterogeneous ET rate found for C His rec-HRP and N His rec-HRP is probably due to the interaction of the histidine tag with the electrode surface. The kinetic data demonstrate that new possibilities for enhancing the catalytic activity of the enzyme at the electrode | solution interface can be achieved by genetic engineering design of the enzyme molecules.

Enantioselective sensor based on microgravimetric quartz crystal microbalance with molecularly imprinted polymer film

Abstract: We report a novel quartz crystal microbalance sensor that provides enantioselectivity to dansylphenylalanine enantiomers by using a molecularly imprinted polymer film as a recognition element. The polymeric recognition thin film, imprinted with chiral dansyl-L-phenylalanine, was immobilised on a gold electrode modified with a photoactive precursor monolayer via a self-assembly process using photopolymerisation. The fabricated sensor was able to discriminate between L- and D-dansylphenylalanine enantiomers in solution owing to the enantioselectivity of the imprinted sites. The enantiomeric composition of L- and D-enantiomeric mixtures could be quantitatively determined by the fabricated sensor. The detection limit is 5 µg mL−1 with a response range of 5–500 µg mL−1 at pH 10.0. The influence of the template concentration on the sensitivity and selectivity of the synthesised polymer membranes was investigated and optimised. The surface characteristics of the polymer coating were studied by varying the pH value of the buffer solution, and a convenient regeneration process was proposed to increase the reproducibility and reusability of the sensor by flushing with pH 2.0 buffer. The selectivity and recognition mechanism of the imprinted polymer film were studied with compounds that are structurally related to the template. The method presented in this work provides a novel means of preparing highly selective and sensitive chemical sensors via self-assembly and molecularly imprinting techniques.

All Solid State Hydrogen Ion Selective Electrode Based on a Tribenzylamine Neutral Carrier in a Poly(vinyl chloride) Membrane with a Poly(aniline) Solid Contact

Abstract: Hydrogen ion selective solid contact electrode based on tribenzylamine have shown the best Nernstian slope, selectivity and the widest response range in Tris buffered pH sample solutions. Their linear dynamic range was pH 2.48–11.21 and Nernstian slope showed 55.1 mV/pH (at 20±0.2 °C). When it was directly applied to human whole blood (in pH range 6.0–8.5), we could get the same satisfying results. This electrode continuously contacted Tris 7.47 buffered solutions, human whole blood and hydrofluoric acid solutions for one month without any loss of performance. Especially, hydrofluoric acid did not influence the surface of this electrode, thus this electrode was maintained without showing any changes in potentials after used in hydrofluoric acid solution. The standard deviation in the e.m.f. differences determined was 1.0 mV (N=10) at Tris buffer solution of pH 6.5 and 0.5 mV at Tris buffer solution of pH 8.5. The 90 % response time of the electrodes obtained by injection of hydrochloric acid into Tris buffer sample solution was less than 8 s.

In vitro dynamic swelling behaviors of polyhydroxamic acid hydrogels in the simulated physiological body fluids

Abstract: Influence of some simulated physiological body fluids on the dynamic swelling behaviour of polyelectrolytic hydroxamic acid hydrogels (PHA) was investigated at 37 °C in vitro. The simulated physiological body fluids are distilled water, human sera, physiological saline (0.89 % NaCl), isoosmotic phosphate buffer at pH 7.4, gastric fluid at pH 1. 1, (gylicine-HCl buffer), urea (0.3 mol L−1), and the aquatic solutions of K2HPO4 and KNO3 (the sources of K+). The values of equilibrium swelling of PHA hydrogels varied in the range of 130–4625%, while the values of equilibrium fluid content of the hydrogels varied in the range of 57–97%. The initial rate of swelling, diffusional exponent, and, diffusion coefficient were calculated using swelling kinetics data. Diffusion of the fluids into the hydrogel was found to be non-Fickian character. The diffusion coefficients of the hydrogel varied between 0.6×10−6– 8.1×10−6 cm2 s−1.

Bioremediation of diesel-contaminated soil by bacterial cells transported by electrokinetics

Abstract: The electrokinetic technology was applied in bioremediation for the purpose of supplying a Pseudomonas strain capable of degrading diesel to contaminated soil bed, and their biodegradation of diesel was carried out after a desired cell distribution was obtained. Electrokinetic injection of the strain was made possible because the cells acted as negatively charged particles at neutral pH, and thus the cells were transported with a precise directionality through the soil mostly by the mechanism of electrophoresis and in part by electroosmosis. A severe pH change in the soil bed was formed due to the penetration of electrolysis products, which was harmful to the cell viability and cell transport. To achieve a desirable cell transport and distribution, the control of pH in soil bed by a recirculating buffer solution in electrode chambers was essential during the application of an electric field. The judicious selections of electrolyte concentration and conductivity were also important for achieving an efficient electrokinetic cell transport since a higher electrolyte concentration favored the maintenance of pH stability in soil bed, but lowered electrophoretic mobility on the other hand. With electrolyte solution of pH 7 phosphate buffer, a 0.05 M concentration showed a better cell transport than 0.02 M and 0.08 M. The cells under pH 8 were transported more efficiently, and even more cell distribution was obtained, compared to the cells under pH 7 or pH 9 in a given time period. Up to 60% of diesel was degraded in 8 days by the Pseudomonas cells, which were distributed electrokinetically under the conditions of pH 8 (1,800 μS/cm, a mixture of phosphate and ammonia buffers) and 40 mA in a soil bed of 15 cm length.

Immobilization of a Series of Dawson Type Heteropolyanions

Abstract: Attempts to immobilize a series of Dawson type heteropolyanions (HPAs) by anodization and the use of polymeric, polyvinylpyridine (PVP), and conducting pyrrole and N-methylpyrrole, films has been undertaken. A stable film of the Dawson Parent, [P2W18O62]6–, HPA was obtained on an anodized carbon electrode, the film exhibited thin layer behavior and was stable up to a pH value of 2.00. The same HPA was successfully immobilized in a protonated PVP film with the resultant modified electrode being stable between pH values of 1.00 and 8.00, with the redox activity of the immobilized HPA exhibiting the same pH dependence as shown by the solution phase species. It was shown that a stable polypyrrole film doped with the Dawson parent HPA was obtained when the cycling of the film was restricted to the first two tungsten-oxo based redox processes in buffer solutions more alkaline than 2.00. The CuII Dawson HPA was successfully immobilized in a polypyrrole matrix exhibiting good stability and clear redox activity for the CuII HPA. Poly(N-methylpyrrole) was found to be the most suitable conducting polymer film for the immobilization of the FeIII Dawson HPA. The film was found to be extremely stable to electrochemical cycling in a buffer solution of pH 4.50. The redox activity of the immobilized HPA was clearly observed and well behaved. In addition to this the electrocatalytic properties of the FeIII HPA towards the reduction of nitrite, as observed in solution, was preserved in the immobilized state.

Microwave Activation of Electrochemical Processes: Square-Wave Voltammetric Stripping Detection of Cadmiumin the Presence of the Surfactant Triton X

Abstract: A novel electrochemical cell based on a flow through system in a microwave cavity is shown to allow voltammetric experiments under microwave conditions. Focusing of the microwave radiation at the electrode-solution (electrolyte) interface creates conditions of extreme localized heating with an inverted thermal gradient within the diffusion layer of the electrode and convective flow. The deposition and anodic stripping detection by square-wave voltammetry of Cd2+ in a 0.1 M acetate buffer solution is shown to be strongly enhanced by microwave activation. The temperature at the electrode-solution interface is calibrated with the reversible redox couple Ru(NH3)63+/2+ in 0.1 M acetate buffer. The effect of microwave activation on the square-wave voltammetric responses for the reduction of Ru(NH3)63+ and for the detection of Cd2+ in 0.1 M acetate buffer solution are studied. In the presence of a nonionic surfactant, Triton X-100, which blocks the electrochemical Cd2+ response under conventional conditions, microwave activation is shown to have a considerable effect in enhancing the sensitivity for Cd2+ detection.

Electrochemical behaviors of quercetin and kaempferol in neutral buffer solution.

Abstract: Ｑｕｅｒｃｅｔｉｎａｎｄｋａｅｍｐｆｅｒｏｌ,ｆｌａｖｏｎｏｌｓ,ａｒｅｐｒｅｄｏｍｉｎａｎｔｉｎｖｅｇｅｔａｂｌｅｓａｎｄｆｒｕｉｔｓ ,ａｎｄａｒｅｃｏｍ ｐｏｎｅｎｔｓｉｎｔｈｅｈｕｍａｎｄｉｅｔ .[1] Ｔｈｅｙａｒｅｒｅｐｏｒｔｅｄｔｏｂｅｐｏｔｅｎｔａｎｔｉｏｘｉｄａｎｔｓ .[2 ,3] Ｏｎｅｍｅｃｈａｎｉｓｍｏｆｔｈｅｉｒａｎｔｉｏｘｉｄａｎｔａｃｔｉｖｉｔｙｉｓｒｅｇａｒｄｅｄａｓｓｃａｖｅｎｇｉｎｇｆｒｅｅｒａｄｉｃａｌｓｂｙｄｏｎａｔｉｏｎｏｆｅｌｅｃｔｒｏｎｓ.[4]Ｓｏｋｎｏｗｌｅｄｇｅａｂｏｕｔｔｈｅｅｌｅｃｔｒｏｃｈｅｍｉｃａｌｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅｓｅｔｗｏｆｌａｖｏｎｏｌｓｃａｎｈｅｌｐｕｓｔｏｕｎｄｅｒｓｔａｎｄｔｈｅｉｒａｎｔｉｏｘｉｄａｎｔａｃｔｉｖｉｔｙ .Ｗｈｅｎｓｔｕｄｙｉｎｇｅｌｅｃｔｒｏｃｈｅｍｉｃａｌｂｅｈａｖｉｏｒｏｆｆｌａｖｏｎｏｉｄｓｉｎｔｈｅｎｅｕｔｒａｌｂｕｆｆｅｒｓｏｌｕｔｉｏｎ ,[5 ] ｗｅｆｏｕｎｄｔｈａｔｑｕｅｒｃｅｔｉｎａｎｄｋａｅｍｐｆｅｒｏｌｇａｖｅａｒｅｖｅｒｓｉｂｌｅａｎｄａｎｉｒｒｅ ｖｅｒｓｉｂｌｅｃｙｃｌｉｃ...