HAc-NaAc Buffer Solution Research Articles

Surface Modification of Nanosized Biphasic α-TCP/HA Powders

Stearic acid was utilized to modify biphasic alpha-tricalcium phosphate (α-TCP)/hydroxyapatite (HA) powders in the ethanol. The results showed that the dispersion of biphasic α-TCP/HA powders (BCPs) in non-polar matrix improved. And the released content of Ca2+ and PO4 3- of the BCPs soaked in the NaAc-HAc buffer solution (pH 5.0) was almost same as that before modification. Stearic acid could modify the suface properties of BCPs and would not obviously affect their biological characteristics, which affords a good groundwork of application of calcium phosphates powders.

Resonance Rayleigh scattering spectrum for the chelate of lanthanum(III) with sodium tanshinon IIA silate and its analytical application

In a pH 3.6–5.0 HAc-NaAc buffer solution, when sodium tanshinon IIA silate (STSIIA) reacts with La(III) to form a chelate, the resonance Rayleigh scattering (RRS) intensity can be enhanced greatly and a new RRS spectrum will appear. The maximum RRS peak is located at 306 nm and the RRS intensity is proportional to the concentration of STSIIA in a certain range. The method is very sensitive and the detection limit for STSIIA (3σ/K) is 82.12 ng·mL−1. The optimum reaction conditions and the effect of coexisting substances have been investigated. A new, simple and fast method for the determination of STSIIA based on RRS method is developed. It can be applied to the determination of STSIIA in the synthesis samples and Nuoxinkang injection. Combined with infrared absorption and NMR spectra, the structure of the chelate and the reasons of RRS enhancement are also discussed.

Spectrophotometric determination of trace copper in water samples with thiomichlersketone

A simple and sensitive spectrophotometric method for determination of trace copper in water samples is proposed. In the presence of pH 4.6 HAc–NaAc buffer solution and surfactant polyethylene octyl phenyl ether (OP) medium, copper reacts with thiomichlersketone (TMK) to form a stable 1:4 complex. The complex Cu(II)–TMK–OP shows maximum absorbance at 500 nm with a molar absorptivity value of 5.7 × 10 4 l mol −1 cm −1. Beer's law is obeyed for copper concentrations in the range of 0–15 μg/25 ml. The average recovery of copper is between 95.8 and 106%. The method has been applied for determination of trace copper in different water samples with satisfactory results.

Simultaneous determination of dinitrophenol isomers with electrochemical method enhanced by surfactant and their mechanisms research

This paper has adopted a fast and convenient analytical technique to detect dinitrophenol isomers directly and simultaneously. In 0.1 mol L −1 HAc–NaAc buffer solution (pH 5.8), 2,4- and 2,5-dinitrophenol exhibited good resolution by DPV at the GC electrode. By using the surfactant of cetyl trimethyl ammonium bromide, the reduction peaks currents were enhanced and the detection sensitivity was improved dramatically. The action mechanism was investigated in detail and some valuable message has been found. The linear calibration ranges from 1.0 × 10 −6 to 8.0 × 10 −4 mol L −1 for both 2,4- and 2,5-dinitrophenol, with detection limits of 2.4 × 10 −7 for 2,4- and 1.5 × 10 −7 mol L −1 for 2,5-dinitrophenol. This method was applied in the determination of dinitrophenol isomers in model water sample, and the recovery was from 98% to 103%.

Synthesis of N-o-Methylphenyl-N′-(sodium p-aminobenzene-sulfonate)thiourea and Its Chromogenic Reaction with Palladium(II)

A new chromogenic reagent, N-o-methylphenyl-N'-(sodium p-aminobenzenesulfonate)thiourea (MSAT), has been synthesized and characterized by elemental analysis, (1)H-NMR, FT-IR and UV-Vis spectra. Based on the absorption spectrum of the colored complex of MSAT with palladium(II), a novel spectrophotometric method for the determination of palladium has been developed. In a pH 4.0 - 5.5 HAc-NaAc buffer solution, palladium(II) reacted with MSAT to form a stable yellow water-soluble complex with an apparent molar absorptivity of epsilon = 2.04 x 10(5) L mol(-1) cm(-1) at the maximum absorption of 318.0 nm. Beer's law was obeyed in the concentration range of 1.2 - 11.8 microg per 25 mL for palladium(II) with a correlation coefficient of 0.9997. The probable interfering ions and their tolerable limits have also been investigated in detail. The proposed method is simple, rapid, and sensitive, and has been applied to the determination of palladium in anode mud and ore samples with satisfactory results.

Studies and Application of Catalytic Kinetic Spectrophotometric Determination of Trace Chromium(VI) Sensitized by Microemulsion Medium

A new catalytic kinetic spectrophotometric method for the determination of trace amount of chromium (VI) in microemulsion medium has been developed. The method is based on the catalytic effect of chromium (VI) on the oxidation of nuclear fast red in the presence of Tween-80 microemulsion and HAc-NaAc buffer solution (pH = 5.2). The linear ranges are in the range of 0 approximately 0.0480 microg mL(-1) of Cr (VI) at 528 nm and the detection limit is 1.56x10(-9)g mL(-1). The method has been applied in determination of Cr (VI) in water and food samples with satisfactory results. The relative standard deviation is less than 4.6 % and the recovery is 93.5 approximately 104 %.

Mercury‐Free Detection of Europium (III) at a Glassy Carbon Electrode Modified with Carbon Nanotubes by Adsorptive Stripping Voltammetry

A multi‐wall carbon nanotubes (MWCNTs) and Nafion composite film‐modified glassy carbon electrode (GCE) is described for the detection of europium (III) by differential pulse adsorptive stripping voltammetry. In pH 4.2 NaAc–HAc buffer solution, Eu3+ is first exchanged by Nafion and absorbed on the surface of MWCNTs film. The accumulated Eu3+ then undergoes a one‐electron reduction around −0.7 V during the potential sweep from −0.1 to −1.0 V. The MWCNTs–Nafion film significantly improves the sensitivity of Eu3+ determination compared with a bare GCE and a Nafion‐coated GCE. The differential pulse stripping voltammetric (DPSV) signal changes linearly with the concentration of Eu3+ in a wide range from 4.0×10−8 to 1.0×10−4 M. The detection limit is estimated to be 10 nM for 60 s accumulation at −0.1 V. Lots of inorganic ions and all of the other rare earth ions do not give characteristic voltammetric responses in the developed operation. The sensitivity and stability of this MWCNTs–Nafion GCE has demonstrated its application for a rapid and mercury‐free detection of trace Eu3+ in NIES CRM No. 8 vehicle exhaust particulates.

Rapid Fluorometric Determination of Trace Indium(III) in Microemulsion Medium after Preconcentration and Separation by Sulphydryl Dextrane Gel

A new highly sensitive, stable, and accurate fluorometric method for the determination of indium(III) has been established in cetyltrimethylammonium bromide(CTMAB) microemulsion media. The excellent color-forming reagent 2,6,7-trihydroxy-9-(3,5-dibromo-4-hydroxyphenyl) fluorone (DBH-PF) reacts with indium(III) to form a purple complex with a 3 : 1 (ligand to metal) ratio in HAc-NaAc buffer solution at pH 4.94. The emission peak occurs at 556 nm with excitation at 525 nm. Indium(III) can be determined in the linear range of 0.005–0.30 µg mL−1 with a detection limit of 0.0029 µg mL−1. Foreign ions are eliminated by preconcentration and separation with sulfhydryl dextranegel (SDG). The proposed method has been satisfactorily examined for the determination of indium(III) in ore and sludge samples. The relative standard deviations are in all instances less than 3.0%, and the recoveries are between 94.7, and 99.5%.

Promoted electron transfer of mitoxantrone binding with DNA by cytochrome c

A promoted electron transfer of an antitumor drug, mitoxantrone (MTX), intercalating into DNA duplex was successfully obtained upon addition of cytochromes c (cyt. c) in NaAc-HAc buffer solution (pH 4.5). The experimental results suggested that co-existence of MTX and cyt. c in the DNA helix is an important factor for accelerated electron transfer of MTX, where the promoter, cyt. c, operated smoothly through the DNA bridge. The UV/Vis spectroscopic experiments further confirmed the interaction process. Furthermore, a possible mechanism of such reaction was also discussed in this paper.

A third-generation hydrogen peroxide biosensor fabricated with hemoglobin and Triton X-100

A new film of Triton X-100 to incorporate hemoglobin for biosensor fabrication is presented in this paper. In this film, hemoglobin displays a pair of redox peaks in pH 6.0 NaAc–HAc buffer solution with a formal potential of −0.257 V (versus SCE) and shows a thin-layer behavior. Without electron mediator or promoter, the modified electrode has an electrocatalytic activity to the reduction of hydrogen peroxide (H 2O 2), which shows a linear dependence on the H 2O 2 concentration ranging from 1.0 × 10 −6 to 1.0 × 10 −4 mol/L. The detection limit of 3.0 × 10 −7 mol/L is estimated when the signal-to-noise ratio is 3. The K M app value of hemoglobin in Triton X-100 film has been determined to be 4.27 mmol/L. Ascorbate, uric acid, dopamine, catechol, cystine and epinephrine will not interfere with the sensitive determination of H 2O 2.

Electrocatalytic Reduction of Oxygen at Multi‐Walled Carbon Nanotubes and Cobalt Porphyrin Modified Glassy Carbon Electrode

AbstractThe multi‐walled carbon nanotubes (MWNTs) modified glassy carbon electrode exhibited electrocatalytic activity to the reduction of oxygen in 0.1 M HAc‐NaAc (pH 3.8) buffer solution. Further modification with cobalt porphyrin film on the MWNTs by adsorption, the resulted modified electrode showed more efficient catalytic activity to O2 reduction. The reduction peak potential of O2 is shifted much more positively to 0.12 V (vs. Ag/AgCl), and the peak current is increased greatly. Cyclic voltammetry (CV), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), were used to characterize the material and the modified film on electrode surface. Electrochemical experiments gave the total number of electron transfer for oxygen reduction as about 3, which indicated a co‐exist process of 2 electrons and 4 electrons for reduction of oxygen at this modified electrode. Meanwhile, the catalytic activities of the multilayer film (MWNTs/CoTMPyP)n prepared by layer‐by‐layer method were investigated, and the results showed that the peak current of O2 reduction increased and the peak potential shifted to a positive direction with the increase of layer numbers.

Simultaneous EQCM and diffuse reflectance UV–visible spectroelectrochemical measurements: poly(aniline-co- o-anthranilic acid) growth and property characterization

Piezoelectric diffuse reflectance spectroelectrochemistry (PDRSEC), a new technique of diffuse reflectance spectroelectrochemistry (DRSEC) in combination with electrochemical quartz crystal microbalance (EQCM), was developed to study the electrochemical copolymerization of aniline and o-anthranilic acid in 1.0 mol l −1 HClO 4 and the properties of these copolymers. The DRSEC using an integral sphere was proven to possess a higher optical sensitivity at the unpolished piezoelectric quartz crystal electrodes used than the mirror reflectance spectroelectrochemistry mode. The copolymers grown from the copolymerization bath of different molar fractions of o-anthranilic acid ( F 1, relative to the total amount of the two monomers) showed intermediate properties between those of the homopolymers, which varied gradually with F 1. The swelling/dissolution behavior of the copolymers vs solution pH was traced via the EQCM frequency and resistance signals, and its large dependence on F 1 was found and discussed. In a HAc–NaAc buffer solution at pH 5.6, the amount of adsorbed lysozyme was found to be positively correlated with F 1, via an EQCM impedance investigation, demonstrating the feasibility of using poly(aniline-co- o-anthranilic acid) as a load-adjustable immobilization matrix for cationic proteins. The novel PDRSEC method proposed is highly recommended for surface electrochemistry studies at relatively rough electrodes.

Determining the Critical Crevice Depth for Iron in a Sodium Acetate-Acetic Acid Buffer Solution

Alloys that depend on oxide films or passive layers for corrosion resistance are susceptible to crevice corrosion. This is for instance the case for iron in a sodium acetate-acetic acid (NaAc-HAc) buffer solution. This material-environment combination shows an active-passive transition in the polarization behavior around (SCE) and, hence, is susceptible to crevice corrosion. Indeed, a potential drop into the crevice might bring part of the crevice into the active region, resulting in crevice corrosion. The potential drop into a crevice in a Fe/NaAc-HAc buffer system has been computed and compared to the experimentally measured profile. Mathematically, the potential drop into the crevice is a Poisson-type field problem with nonlinear boundary conditions and it has been described in a one-dimensional finite difference framework. The subsequent critical depth calculations, determining the onset of crevice corrosions, were solely based on the geometry of the crevice, the conductivity and the polarization behavior of iron in a NaAc-HAc buffer solution. In order to achieve this, a Weibull transition function has been used to describe the active-to-passive transition in the polarization behavior. Due to the strongly nonlinear and inherently nonmonotonic character of the boundary conditions (the active-passive transition in the polarization behavior), the resulting equations are solved using a generally applicable homotopy method. © 2003 The Electrochemical Society. All rights reserved.

Investigation of the electrocatalytic behavior of single-wall carbon nanotube films on an Au electrode

The voltammetric behavior of uric acid (UA) was studied with an Au electrode modified with single-wall carbon nanotubes (SWNTs). In 0.1 M HAc–NaAc buffer solution (pH 5.0), the SWNT-modified electrode shows high electrocatalytic activity toward UA oxidation. The electro-oxidation of UA is an irreversible diffusion-controlled process with a diffusion coefficient ( D) of 8.85×10 −6 cm 2 s −1. The peak current increases linearly with the concentration of UA in the range of 4.0×10 −6–7.0×10 −4 M. The detection limit is 1.0×10 −6 M. The SWNT was characterized with scanning electron microscopy (SEM). Furthermore, the SWNT-modified electrode has favorable electrocatalytic activity toward dopamine and norepinephrine. This SWNT-modified electrode can also separate the electrochemical responses of uric acid, norepinephrine and ascorbic acid.

Determination of antimony(III) in environmental water samples in microemulsion system by the fluorescence quenching method

A novel highly sensitive and selective fluorescent reagent, 2,6,7-trihydroxy-9-(3,5-dibromo-4-hydroxyphenyl)fluorone (DBH-PF) has been studied for the spectrofluorimetic determination of antimony(III) in cetyltrimethylammonium bromide (CTMAB) microemulsion media. DBH-PF reacts with antimony(III) forming a complex with 1:2 (metal to ligand) antimony–DBH-PF in the system of HAc–NaAc buffer solution at pH 5.33. The maximum excitation and emission wavelengths are at 522 and 556 nm, respectively. The linear range of the method is 0.05∼1.50 μg 10 ml −1 and the detection limit is 0.015 μg 10 ml −1. Foreign ions are eliminated by preconcentration and separation with sulfhydryl dextrose gel (SDG) at pH 1.0. The proposed method has been applied to the determination of antimony(III) in industrial waste water samples with satisfactory results.

SPECTROPHOTOMETRIC DETERMINATION OF COPPER AND PALLADIUM USING A NEW REAGENT

ABSTRACT Highly sensitive spectrophotometric methods for determination of copper and palladium by a new synthesized chromogenic reagent N-dodecyl-N′-(sodium p-amino-benzenesulfonate)-thiourea (DOPT) were developed. In the presence of CTMAB and NaAc-HAc buffer solution, under the optimum conditions for color reaction of copper and palladium with DOPT, their molar absorptivities are ε300.4 nm = 1.56 × 105 l mol−1 cm−1 at 300.4 nm for copper and ε296.0 nm = 7.41 × 104 l mol−1 cm−1 at 296.0 nm for palladium. Microamounts of copper and palladium in samples were satisfactorily determined by the methods.

Studies on the Electrochemical Behaviour of Hydroquinone at L-cysteine Self-Assembled Monolayers Modified Gold Electrode

L-Cysteine is combined onto gold electrode to form a self-assembled monolayers modified electrode (L-Cys/Au SAMs) by taking advantage of strong sulfur-gold interaction. ATR-FTIR, SEM, cyclic voltammetry (CV) and impedance were used for the characterization of the film. It shows excellent stability upon voltametric scanning and a good voltametric response towards hydroquinone with the potential ranged from 0.8 to –0.2 V (vs.SCE) in 0.5M HAc-NaAc buffer solution (pH 4.8). The oxidation potential of hydroquinone on the modified electrode shifted negatively about 330 mV as compared with the bare gold electrode. The plot of catalytic current vs.its concentration has a good linear relation in the range of 2.0×10-6~2.0×10-4M with the correlation coefficient of 0.9986 and the detection limit of 4.0×10-7M by different pulse voltammetry (DPV). Mechanism for the electrocatalytical process has been studied.

Neurotransmitter dopamine applied in electrochemical determination of aluminum in drinking waters and biological samples

It was demonstrated that the decrease of the differential pulse voltammetric (DPV) anodic peak current of dopamine (3,4-dihydroxyphenylethylamine, DA) was linear with the increase of aluminum (Al) concentration. Under optimum experimental conditions (pH 4.6, 1.2×10 −3 M DA, and 0.04 M NaAc–HAc buffer solution), the linear range is 4.0×10 −7–8.0×10 −5 M, the detection limit is 1.4×10 −7 M, and the relative standard deviation for 4×10 −5 M Al III is 3.5% ( n=8). Many foreign species, especially some low-molecule-weight biological molecules, were chosen for interference testing. The proposed method was applied to the determination of Al in biological samples such as synthetic renal dialysate, Ringer’s solution, human blood, cerebrospinal fluid of a patient, and urine of a diabetic patient. The corresponding recoveries were generally between 95 and 105%. The basic principle of the method was determined by examining Al complexed with DA. This results in the blockage of the electroactive sites on DA, followed eventually by the reduction of the electrochemical response of DA. This result was verified by examining the behavior of DA, both in the presence and absence of Al, using electrochemical, UV–Vis, Raman, and 13C NMR spectroscopic methods.

Electrocatalytic oxidation of 3,4-dihydroxyphenylacetic acid at a glassy carbon electrode modified with single-wall carbon nanotubes

Abstract The voltammetric behavior of 3,4-dihydroxyphenylacetic acid (DOPAC) was studied at a glassy carbon (GC) electrode modified with single-wall carbon nanotubes (SWNTs). In 0.1 M HAc–NaAc buffer solution (pH 4.4), the SWNT-modified electrode shows high electrocatalytic activity toward oxidation of DOPAC. One well-defined redox couple is obtained. The peak current increases linearly with the concentration of DOPAC in the range of 1.0×10 −6 –1.2×10 −4 M. The detection limit is 4.0×10 −7 M. The results indicate that DOPAC undergoes a two-electron oxidation to o -quinone followed by a dimerization reaction. Rate constant for this dimerization reaction was calculated to be 2.10×10 3 dm 3 mol −1 s −1 . The SWNT was characterized with scanning electron microscope (SEM). This SWNT-modified electrode can also separate the electrochemical responses of DOPAC and 5-hydroxytryptamine (5HT).

A high-selectivity spectrophotometric reagent for determining platinum(IV)

The new reagent N-(m-Methylphenyl)- N′-(sodium p-aminobenzenesulfonate)-thiourea (MMPT) was synthesized and its structure was confirmed by elemental analysis, IR, UV and 1HNMR spectra. The apparent molar absorptivities of usual ions were determined and the chromogenic reaction with microamounts of platinum(IV) was studied in detail. In the medium of an HAc-NaAc buffer solution, MMPT can react with platinum(IV) to form a green soluble complex. The maximum absorbance of the complex is at 754.4 nm ( ε 754.4=8.58×10 4 L·mol −1·cm −1) and 332.8 nm ( ε 332.8=1.14×10 5 L·mol −1·cm −1). Beer's law was obeyed for platinum concentrations in the range of 0∼1.28 mg·L −1; the correlation coefficient was r=0.9995. At 754.4 nm, over 50 ions did not interfere with the reaction. It is one of the simplest and most selective methods available. It was convenient and rapid and has been applied to the direct determination of Pt(IV) in ores and catalysts with satisfactory results.