Showing papers on "Buffer solution published in 2000"

Electrochemical pretreatment of polycrystalline gold electrodes to produce a reproducible surface roughness for self-assembly: a study in phosphate buffer pH 7.4

Abstract: It has been emphasized in several studies that the state of the surface, including the surface roughness, is very important for the reproducible formation of high-quality self-assembled monolayers on gold. The pulsed-potential pretreatment procedure described in this paper can, in a reproducible way, reduce the surface roughness of mechanically polished polycrystalline gold electrodes by a factor 2. The developed procedure, in which the gold is alternately oxidized and reduced, has been optimized for use in a flow system (100 mM phosphate buffer pH 7.4). The influence of the pretreatment procedure on the surface roughness of the electrodes has been studied by in-situ oxygen adsorption measurements using cyclic voltammetry. The most effective pulse regime in producing a gold surface with a reproducible and relatively low surface roughness is a triple-potential pulse waveform, with potentials of +1.6, 0.0, and −0.8 V vs SCE and pulse widths of 100 ms for each potential. Prolonged pulsing for 2000−5000 s wit...

Preparation of porous resin loaded with crystalline hydrous zirconium oxide and its application to the removal of arsenic

Abstract: A porous resin loaded with monoclinic or cubic hydrous zirconium oxide was prepared by incorporation of ZrOCl 2 ·8H 2 O into porous spherical polymer beads followed by hydrolysis and hydrothermal treatment of the zirconium salt. Hydrous zirconium oxide appeared to deposit inside the pores with relatively large diameter. The adsorption capacity and distribution coefficients for As(III) and As(V) were determined by batch procedures. The hydrous zirconium oxide-loaded resin (Zr resin) showed a strong adsorption for As(V) at slightly acidic to neutral pH region while As(III) was favorably adsorbed at pH around 9 to 10. The removal of low concentrations of arsenic from the model effluents to meet the demand of Japanese industrial effluent standard (0.1 ppm) was successfully achieved by the column operation packed with the Zr resin. The Zr resin was regenerated by treatment of the column with 1 M sodium hydroxide followed by conditioning with 0.2 M acetate buffer solution. The amount of zirconium leached out during the adsorption and regeneration cycles was negligibly small and the column can be used repeatedly.

Adsorption of Some Heavy Metal Ions from Aqueous Solution by Activated Carbon and Comparison of Percent Adsorption Results of Activated Carbon with those of Some Other Adsorbents

Abstract: In this study, removal of some heavy metals ions (Mn2+, Fe2+, Ni2+ and Cu2+) from aqueous solution by adsorption was investigated. For this purpose, high-grade MnSO4.H2O, FeSO4.7H2O, NiSO4.7H2O and CuSO4.5H2O were used as heavy metal samples. The commercial activated carbon (Merck 2514), chitosan and agar were used as adsorbents. The pH of each solution was not controlled. This is because the net interaction between the adsorbent and the heavy metal could be disturbed by the buffer solution. Therefore, all experiments were carried out in a pH range from 5.3 to 5.5. The equilibrium adsorption contact times were determined for M - 2514. The adsorption rate constants were determined from obtained kinetics curves suitable for first degree of rate kinetics. Adsorption isotherms of heavy metals on M - 2514 from aqueous solution were determined. These adsorption isotherms were seen to be consistent with Freundlich's adsorption isotherm. k and n constants were determined from Freundlich's linear equation. In addition, M - 2514, chitosan and agar were compared according to their percent uptake yields of the heavy metals.

The Passivity of Iron in the Presence of Ethylenediaminetetraacetic Acid I. General Electrochemical Behavior

Abstract: The effect of EDTA (ethylenediaminetetraacetic acid, added as ) on the electrochemical behavior of iron and on the semiconducting properties of passive films formed on this metal in borate buffer solution (pH 8.4) was studied. Electrochemical studies, including potentiodynamic and galvanostatic reduction experiments and capacitance measurements coupled with Mott‐Schottky analysis, were carried out over the entire passive range in borate buffer solutions in the presence and absence of 0.01 M EDTA. Passive films formed in the presence of EDTA were thinner and showed higher donor concentrations. EDTA present in the borate buffer solution effectively inhibited the formation of the Fe(III) outer layer, thereby rendering the defective inner layer to direct examination. The barrier layer is found to be an n‐type semiconductor, which is consistent with the oxide being a defective magnetite in which the principal defects are oxygen vacancies and cation interstitials. EDTA effectively competes with chloride ion for adsorption into oxygen vacancies at the barrier layer/solution interface, thereby suggesting that the chelating agent might be an effective inhibitor of passivity breakdown. © 2000 The Electrochemical Society. All rights reserved.

Sensor for hydrogen peroxide based on Prussian blue modified electrode : Improvement of the operational stability

Abstract: Improvement of the operational stability of amperometric sensors based on Prussian Blue (PB) modified glassy carbon electrodes is presented. The long term performance of the sensors was evaluated by injection of hydrogen peroxide (5 µM in potassium buffer) solutions in a flow-injection system during a period of 5 ‐10 h. The following parameters were investigated and correlated with the performance of the sensor: the times for electrodeposition and electrochemical activation, temperature, storage time, pH, composition of the buffer solution and of volume sample injected. These analytical characteristics of the modified electrode can be emphasized: initial sensitivity of 0.3 A cm ‐2 M ‐1 , detection limit of ca. 0.5 µM, precise results (r.s.d.< 1.5%) and possibility to carry out around 50 samples (50 µL) per hour.

Studies on the 1,1-Diphenyl-2-picrylhydrazyl Radical Scavenging Mechanism for a 2-Pyrone Compound

Abstract: The radical scavenging mechanisms for the 2-pyrone compound, 4-hydroxy-3,6-dimethyl-2H-pyrane-2-one (1), and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical (4) in several solvent systems were evaluated by the quantitative change in compounds detected at 270 nm and subsequent HPLC analyses. The HPLC profile for each condition suggested that the reaction proceeded by a different mechanism in each solvent system. In organic solvents (CHCl3, iso-propanol, and EtOH), 1-[4-(3,4-dihydro-3,6-dimethyl-2,4-dioxo-2H-pyran-3-yl) phenyl]-1-phenyl-2-picrylhydrazine (2) was produced as an adduct of the DPPH radical and 1. On the other hand, the reaction in a buffer solution (an acetate buffer at pH 5.5) gave several degradation products with 1[4-(2,3-dihydro-2,5-dimethyl-3-oxo-fur-2-yl) phenyl]-1-phenyl-2-picrylhydrazine (5), this being structurally elucidated by spectroscopic analyses. The decrease of the DPPH radical in each reaction system suggests that compound 1 could scavenge about 1.5-1.8 equivalents of the radical in organic solvents and about 3.5-3.9 in the buffer solution.

Simultaneous determination of Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe in water samples by differential pulse stripping voltammetry at a hanging mercury drop electrode

Abstract: A highly sensitive and selective voltammetric procedure is described for the simultaneous determination of eleven elements (Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe) in water samples. Firstly, differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode (HMDE) is used for the direct simultaneous determination of Cd, Pb, Cu, Sb and Bi in 0.1 M HCl solution (pH = 1) containing 2 M NaCl. Then, differential pulse cathodic stripping voltammetry (DPCSV) is used for the determination of Se in the same solution. Zn is subsequently determined by DPASV after raising the pH of the same solution to pH 4. Next, the pH of the medium is raised to pH 8.5 by adding NH3/NH4Cl buffer solution for the determination of Mn by DPASV. Ni and Co are determined in the same solution by differential pulse adsorptive stripping voltammetry (DPAdSV) after adding DMG (1 × 10–4 M). Finally, 1 × 10–5 M 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is added to the solution for the determination of Fe by DPAdSV. The optimal conditions are described. Relative standard deviations and relative errors are calculated for the eleven elements at three different concentration levels. The lower detection limits for the investigated elements range from 1.11 × 10–10 to 1.05 × 10–9 M, depending on the element determined. The proposed analysis scheme was applied for the determination of these eleven elements in some ground water samples.

Extraction of mineralizable organic nitrogen from soils by a neutral phosphate buffer solution

Abstract: The availability of soil nitrogen is often evaluated based on the amount of released inorganic N during incubation of a soil at 30°C under field moisture conditions (called the “incubation method”). In place of the incubation method, however, we have developed a phosphate buffer extraction method, as phosphate buffer-extractable organic nitrogen (PEON) appears to correlate strongly ( r=0.92 ∗∗∗ ) with the inorganic N obtained by the incubation method, based on an analysis of 20 soil samples collected from various soil types. The substances in the soil solutions extracted with phosphate buffer were analyzed with size-exclusion HPLC equipped with a UV detector (280 nm) and sodium dodecyl sulfate-polyacrylamid gel electrophoresis (SDS–PAGE). One major peak was detected in HPLC chromatograms irrespective of the soil types. The peak area in the HPLC showed a high correlation with both, the amount of PEON and the protein concentration in the soil solutions extracted with phosphate buffer. Further, the major peak detected in size-exclusion HPLC was identified as a uniform protein-like N compound as the SDS–PAGE results showed only a major band and the molecular weight of the band corresponded to that of the major peak. In order to determine the origin of this homogeneous N compound that appears as one major band in the SDS–PAGE, three kinds of organic materials (glucose and ammonium sulfate, a 4:1 mixture of rice bran and rice straw, and rapeseed cake) were added to soil and their soil solutions extracted with phosphate buffer were traced using SDS–PAGE. The original bands of the organic materials disappeared rapidly on the separation gel, and one major band that was present in the primary soil increased, even though different organic materials had been applied. However, when chloramphenicol and organic materials were added simultaneously, the appearance of this major band was retarded, but when cycloheximide and organic materials were added, the major band appeared more rapidly than in the case of organic materials without any antibiotic. Therefore, we were able to confirm that the source of mineralizable N may be a homogeneously-produced protein-like N compound derived from soil bacteria with a distinct molecular weight (about 8000–9000 Da).

The decomposition of peroxynitrite to nitroxyl anion (NO-) and singlet oxygen in aqueous solution.

Abstract: The mechanism of decomposition of peroxynitrite (OONO−) in aqueous sodium phosphate buffer solution at neutral pH was investigated. The OONO− was synthesized by directly reacting nitric oxide with superoxide anion at pH 13. The hypothesis was explored that OONO−, after protonation at pH 7.0 to HOONO, decomposes into 1O2 and HNO according to a spin-conserved unimolecular mechanism. Small aliquots of the concentrated alkaline OONO− solution were added to a buffer solution (final pH 7.0–7.2), and the formation of 1O2 and NO− in high yields was observed. The 1O2 generated was trapped as the transannular peroxide (DPAO2) of 9,10-diphenylanthracene (DPA) dissolved in carbon tetrachloride. The nitroxyl anion (NO−) formed from HNO (pKa 4.5) was trapped as nitrosylhemoglobin (HbNO) in an aqueous methemoglobin (MetHb) solution. In the presence of 25 mM sodium bicarbonate, which is known to accelerate the rate of decomposition of OONO−, the amount of singlet oxygen trapped was reduced by a factor of ≈2 whereas the yield of trapping of NO− by methemoglobin remained unaffected. Because NO3− is known to be the ultimate decomposition product of OONO−, these results suggest that the nitrate anion is not formed by a direct isomerization of OONO−, but by an indirect route originating from NO−.

Doping behavior of water-soluble π-conjugated polythiophenes depending on pH and interaction of the polymer with DNA

Abstract: Doping behavior of two kinds of water-soluble polythiophenes (PThs) (PTh with a CH 2 CH 2 CH 2 SO 3 M substituent at the 3-position, P3(RSO 3 H)Th, and poly(ethylenedioxythiophene), PEDOTh) has been investigated spectroscopically at various pH under air. The p-doped (or oxidized) state of P3(RSO 3 M)Th is stable at pH=1.0, whereas at pH levels higher than 4, the polymer is undoped. To the contrary, the p-doped state of PEDOTh is stable over a pH range of 1 to 7. Mixing of PEDOTh and a DNA (poly(G-C) 2 ) in a Tris buffer solution leads to a change of the UV-visible spectrum and precipitation of their adduct, supporting formation of an adduct between PEDOTh and poly(G-C) 2 .

Determination of the Ionization State of 11-Thioundecyl-1-phosphonic Acid in Self-Assembled Monolayers by Chemical Force Microscopy

Abstract: The present article describes the preparation and preliminary characterization of a novel phosphate-functionalized self-assembled monolayer (SAM) and the determination of the surface ionization states of the phosphate headgroup in aqueous solutions by chemical force microscopy (CFM). The phosphate headgroup used was PO(OH)2, a diprotic acid. The adhesion force between an AFM probe and a flat substrate, both of which were chemically modified with the same phosphate SAM, was also measured as a function of pH and ionic strength. At low ionic strength (10-4 M), two peaks were observed in the force titration curve (adhesion force versus pH) at pH 4.5 and 8.4. The two peaks are positioned 2.4 and 1.2 pH units higher, respectively, than the acid dissociation constants obtained for the phosphate group free in aqueous solution. At high ionic strength (10-1 M), the adhesion forces were reduced by 1 order of magnitude and the peaks were replaced by shoulders similar to those previously reported for acid force titrat...

A dual electrochemical sensor for nitrite and nitric oxide.

Abstract: Nafion/lead-ruthenate pyrochlore chemically modified electrode (NPyCME) showed a remarkable dual sensing activity toward NO2− oxidation and NO reduction as demonstrated by cyclic voltammetry (CV), ac-impedance spectroscopy and flow injection analysis (FIA). The mechanistic parameters of current function, charge transfer resistance and exchange current for the NPyCME, GCE and Nafion-coated GCE were evaluated and compared. The disproportionation reaction of NIIIO2− into NIVO3− + NIIO in acidic solution was used as a model system for testing the dual sensing ability of the NPyCME. The obtained crossover peak response for NO2− oxidation and NO reduction in pH 1.65 buffer solution gave the direct proof for the applicability of the NPyCME in the dual electrocatalytic action. By flow injection analysis, under optimized conditions, the calibration curve was linear in the range of 100 nM–100 µM and 800 nM–63.3 µM and the detection limit (S/N = 3) was 4.8 nM and 15.6 nM for NO2− and NO, respectively.

Separation of anthraquinones by capillary electrophoresis and high-performance liquid chromatography.

Abstract: The separation and determination of twelve anthraquinones, viz. anthraquinone 1, chrysphanol 2, aloe-emodin 3, alizarin 4, anthraquinone-2-carboxylic acid 5, purpurin 6, sennoside B 7, sennoside A 8, emodin 9, quinalizarin 10, rhein 11, and anthraflavic acid 12, were achieved by capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). Detection at 260 nm with a buffer solution containing 30 mM sodium borate (adjusted to pH = 10.56 with 0.05N NaOH) and acetonitrile (9:1) in CE or with a linear gradient elution containing 20 mM KH 2 PO 4 with 0.05% phosphoric acid (pH = 2.91) and methanol in HPLC was found to be the most suitable approach for this separation. Contents of six components (2, 3, 7, 8, 9, 11) in crude Rhei Rhizoma extract could easily be determined within 39 min by CE or 63 min by HPLC. The effects of buffers on this separation and the validation of the two methods were studied.

A capillary electrophoretic reactor with an electroosmosis control method for measurement of dissociation kinetics of metal complexes

Abstract: The solvolytic dissociation rate constants of 1:2 complexes of Al 3+ and Ga 3+ with an azo dye ligand, 2,2'-dihydroxyazobenzene-5,5'-disulfonate (DHABS, H 2 L 2- ), have been evaluated with a capillary electrophoretic reactor (CER) system. This CER system is based on the fact that metal complexes encounter an overwhelming force to dissociate when apart from the ligand by CE resolution. Treatment of a capillary with a slightly acidic buffer solution, e.g., pH 5, reduces the double-layer potential (ζ) of the inner silica wall. Owing to slow relaxation of the deprotonation equilibria of superficial silanol groups known as the pH hysteresis, this ζ potential can be actually retained during the electrophoresis of the metal complexes in question with a neutral buffer at pH 7.0. This method enables one to manipulate migration times, namely, residence times in a capillary tube, from 5 to 90 min, depending on the prescribed conditioning pH, without changing any other operation conditions such as buffer composition and electric field strength. The excellent performance of the CER is exemplified by the accurate estimation of the dissociation degree of the complexes. The dissociation degree-time profiles for the complexes are quantitatively described using both internal and external standards; the very inert complex of [Co III L 2 ] 5- for the peak signal standardization and methyl orange for the injection volume correction. The solvolytic dissociation rate constants of the 1:2 complexes of Al 3+ and Ga 3+ ions with DHABS [AlL 2 ] 5- and [GaL 2 ] 5- into the 1:1 ones have been determined as (4.9 ± 1.0) × 10 -4 and (3.7 ± 0.3) × 10 -3 s -1 at 303 K, respectively.