HAc-NaAc Buffer Solution Research Articles

Determination of levofloxacin hydrochloride with multiwalled carbon nanotubes-polymeric alizarin film modified electrode

Multiwalled carbon nanotubes-polymeric alizarin film modified electrode was made. The electrochemical behavior of levofloxacin hydrochloride on modified electrode was studied with cyclic voltammetry, linear sweep voltammetry and chronopotentiometry. The results indicated that the electrical oxidation of levofloxacin hydrochloride on MWNT-PAR electrode, in HAc-NaAc buffer solution at pH 4.2 was irreversible and was controlled by diffusion. Some important parameters m, n, D, ED, ΔSrc and ΔHrc of the electrochemical process were evaluated. Good linearity relationship between peak current and its concentration in the range of 5.0 × 10−6–1.0 × 10−4 mol l−1 was found, of which the equation was Ip(A) = −5.456 × 10−6 0.2667c, the correlative coefficient r = −0.9976 and detect limitation was 4.0 × 10−7 mol l−1. The recovery of levofloxacin hydrochloride in levofloxacin hydrochloride injection was between 94.6 and 104.7%.

A novel electrochemical method for the determination of trinitrophenol

In pH 5.5, 0.1 mol l−1 HAc-NaAc buffer solution, trinitrophenol has been determined quantitatively with differential pulse voltammetry by detecting its reduction peak currents at the glassy carbon electrode. The detection sensitivity was enhanced significantly by the addition of the surfactant of cetyl pyridinium chloride, and the enhancement mechanism was also studied in detail. The linear calibration range was 8.0 × 10−7 to 2.0 × 10−4 mol l−1, and the detection limit was established to be 1.9 × 10−7 mol l−1. This method has been applied to the determination of trinitrophenol in water sample, and the recovery was from 97.6 to 103.5%.

Effects of Chlorine Ion on the Photocatalytic Activity of Cuprous Oxide Powders Prepared by Hydrothermal Method

Cuprous oxide(Cu2O) microcrystals were successfully synthesized via hydrothermal method using CuSO4•5H2O and Na2SO3 in HAc-NaAc buffer solution. The products were characterized by X-rays diffraction (XRD) ,scan election microscopy (SEM) and ultraviolet-visible (UV-vis) spectroscopy. The photocatalytic activity of the as-prepared Cu2O powders was evaluated by the photocatalytic degradation of methyl orange solution under visible light irradiation at room temperature in air. The effects of chlorine ion on the photocatalytic activity of the Cu2O powders were investigated and discussed. The results show that chlorine ion in solution can obviously decrease the photocatalytic activity of Cu2O. When the concentration of chlorine ion increased to 0.5mol/L(about Cl- concentration in the seawater), the photocatalytic ratio of Cu2O decrease to 45% compared with the value in pure water. Increasing solution pH can enhance the photocatalytic activity of Cu2O. The mechanism of photo-degradation was discussed.

Voltammetric Determination of In3+ Based on the Bifunctionality of a Multi-walled Carbon Nanotubes-Nafion Modified Electrode

Due to the strong cation-exchange ability of Nafion and the excellent properties of multi-walled carbon nanotubes (MWCNTs), a highly sensitive and mercury-free method of determining trace levels of In(3+) has been established based on the bifunctionality of a MWCNTs/Nafion modified glassy carbon electrode (GCE). The MWCNTs/Nafion modified GCE detects In(3+) in a 0.01 M HAc-NaAc buffer solution at pH 5.0 using anodic stripping voltammetry (ASV). The experimental results suggest that a sensitive anodic stripping peak appears at -0.58 V on anodic stripping voltammograms, which can be used as an analytical signal for the determination of In(3+). A good linear relationship between the stripping peak currents and the In(3+) concentration is obtained, covering the concentration range from 5.0 x 10(-10) to 2.0 x 10(-7) M, with a correlation coefficient of 0.999; the detection limit is 1.0 x 10(-11) M. This proposed method has been applied to detect In(3+) as a new way.

A new spectrofluorimetric method for determination of trace amounts histamine in human urine and serum

A new spectrofluorimetric method was developed for the determination of trace amounts of histamine in human urine and serum samples. In NaAc-HAc buffer solution of pH 4.0, histamine can react with the acetylacetone-formaldehyde system to produce a fluorescent derivative which emits yellow-green fluorescence at 476 nm, according to the Hantzsch reaction, and the enhanced fluorescence intensity is in proportion to the concentration of histamine. Optimum conditions for the determination of histamine were also investigated. The dynamic range and detection limit for the determination of histamine is 5.96 x 10(-8)-1.50 x 10(-5 )mol/L and 4.35 x 10(-8)mol/L, respectively. This method is practical and can be successfully applied to determination of histamine in human urine and serum samples. A proposal of the reaction pathway is suggested.

Mesoporous titanosilicates with high loading of titanium synthesized in mild acidic buffer solution

Mesoporous titanosilicates with high titanium content were synthesized under mild acidic conditions (pH = 4.4, HAc–NaAc buffer solution) by co-condensation of acetylacetone-modified titanium isopropoxide (Ti(OBu n ) 3 (acac)) and mixture of sodium silicate with tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS) or tetrakis(2-hydroxyethyl)orthosilicate (EGMS), using block copolymer Pluronic P123 as template. The combined results of XRD, N 2 sorption and TEM show that the highly regular structure of the mesoporous titanosilicates can still be obtained when Ti/Si molar ratio in the final product is as high as 0.059. The results of UV–vis diffuse reflectance spectra and UV resonance Raman spectra show that the framework titanium species are predominant in the mesoporous titanosilicates when Ti/Si molar ratio in the final product is less than 0.042. The mixture of sodium silicate and EGMS was proved to be the best silicon source for the synthesis of titanosilicates with ordered mesostructure and high titanium content. The efficiency of this synthetic method may be attributed to the mild acidic medium as well as the modified hydrolysis–condensation rate and hydrophility of the precursors.

Electrochemical determination of phloroglucinol using a carbon nanotube modified electrode enhanced by surfactant

A novel technique is utilized to detect trace amounts of phloroglucinol. In pH 5.0, 0.1 mol L−1 HAc–NaAc buffer solution, phloroglucinol exhibited a stable and sensitive oxidation signal at a glassy carbon electrode modified with multi-wall carbon nanotube. By using the surfactant cetyl pyridinium chloride, the electrochemical response was greatly enhanced. The mechanism was systematically explored. In the range 9.0 × 10−7–3.0 × 10−4 mol L−1, the oxidation peak currents of phloroglucinol have a linear relationship with concentration: the limit of detection was estimated to be 2.5 × 10−7 mol L−1 (S/N = 3). The method was adopted to detect the content of phloroglucinol injection, and the recovery was from 97.5% to 103.0%.

Electrochemical determination of ferulic acid in Chinese traditional medicine Xiao Yao Pills at electrode modified with carbon nanotube

The electrochemical behaviors of ferulic acid were investigated at the glassy carbon electrode modified with multi-walled carbon nanotube. In pH 5.5, 0.1 mol l−1 HAc-NaAc buffer solution, ferulic acid exhibited a pair of stable and sensitive redox signals at the modified electrode. The reaction mechanism was explored. Through the cyclic voltammetry, trace amount of ferulic acid was detected quantitatively. In the range of 1 × 10−5 to 5 × 10−3 mol l−1, the oxidation peak currents of ferulic acid have a linear relationship to the concentrations, the limit of detection was estimated to be 1 × 10−7 mol l−1 (S/N = 3). The influences of substrate, pH and interference of coexisting substances were investigated for response properties of the electrode. Actual Xiao Yao Pill samples were analyzed and satisfactory results were obtained, which meant that the method could be used to detect the trace amount of ferulic acid in medicament.

A facile and fast electrochemical method for the simultaneous determination of o-dihydroxybenzene and p-dihydroxybenzene using a surfactant

A fast and convenient analytical technique has been suggested to detect dihydroxybenzene (DHB) isomers directly and simultaneously. In 0.1 M HAc-NaAc buffer solution (pH 5.6), the reduction peaks of p -DHB and o -DHB were partly separated by differential pulse voltammetry at the glassy carbon electrode. By adding a surfactant (cetyl pyridinium chloride) to enhance the detection sensitivity and using a semi-derivative technique to improve the separation, p-DHB and o-DHB were detected simultaneously. The linear calibration ranges were 1.2 × 10−6 to 1.0 × 10−4 M for p -DHB and 8.2 × 10−7 to 1.0 × 10−4 M for o -DHB, with detection limits of 3.6 × 10−7 and 2.4 × 10−7 M, respectively. The proposed method has been applied to the direct determination of DHB isomers in water sample, and the results were excellent.

Effect of pH on sorption for RE(III) and sorption behaviors of Sm(III) by D152 resin

The pH dependent sorption of rare earth ions (La(III), Ce(III), Pr(III), Nd(III), Y(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Lu(III), and Yb(III)) from HAC-NaAC buffer solution at 298 K by D152 resin containing -COOH function groups were presented. The sorption behaviors of D152 resin for Sm(III) were discussed as an example. The effects of operational conditions such as pH, temperature, and contact time were studied. The statically saturated sorption capacity was 510 mg/g resin at pH 6.70 in HAc-NaAc medium at 298 K. The sorption behaviors obeyed the Freundlich isotherm. The capacity value for column study was obtained by graphical integration as 495 mg/g resin. Thomas model was applied to experimental data to predict the breakthrough curve and to determine the characteristic parameters of the column useful for process design.

A hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin incorporated in PEO–PPO–PEO triblock copolymer film

A new film of triblock copolymer EO 20PO 70EO 20 (P123) was used to incorporate hemoglobin (Hb) onto the surface of pyrolytic graphite (PG) electrode for biosensor fabrication. UV–vis spectra suggested that Hb in the film could keep its native secondary structure. A pair of stable, well-defined and quasi-reversible cyclic voltammetric peaks was observed with the formal potential of about −0.29 V (vs. SCE) at the Hb/P123 film-modified electrode in pH 6.0 NaAc–HAc buffer solution, characteristic of heme Fe III/Fe II redox couple of Hb. The modified electrode exhibited good electrocatalytic activity to the reduction of hydrogen peroxide (H 2O 2). The linear concentration range of the unmediated H 2O 2 biosensor was from 1.0 × 10 −6 to 5.0 × 10 −4 M with a detection limit of 5.0 × 10 −7 M. The apparent Michaelis–Menten constant of Hb in the P123 film was estimated to be 0.51 mM, showing its high affinity. The stability, reproducibility and selectivity of the biosensor were also evaluated.

Study on the interaction between palladium(II)–lincomycin chelate and erythosine by absorption, fluorescence and resonance Rayleigh scattering spectra and its analytical applications

In pH 5.0-5.4 HAc-NaAc buffer solution, lincomycin (Linco) reacted with Pd(II) to form 1:1 cationic chelate, which could further react with erythrosine (Ery) to form 1:1 ion-association complexes (Pd-Linco)Ery. As a result, not only were the absorption and fluorescence spectra changed, but also the resonance Rayleigh scattering (RRS) intensity was greatly enhanced. These phenomena offered useful means for the determination of Linco by spectrophotometry, fluorescence and RRS methods. The linear range and detection limit of Linco were 0.20-3.00 microg/mL and 0.057 microg/mL, 0.20-4.80 microg/mL and 0.061 microg/mL, 0.05-2.70 microg/mL and 0.015 microg/mL for the spectrophotometric, fluorescence quenching and RRS methods, respectively. Among these, the RRS method obtained the highest sensitivity. Therefore, the optimum reaction conditions and the influences of coexisting substances were investigated using the RRS method. A simple, sensitive and rapid method has been developed for the determination of Linco in either the pharmaceutical form or human body fluids, and the reasons for RRS enhancement are discussed.

Derivative voltammetric direct simultaneous determination of nitrophenol isomers at a carbon nanotube modified electrode

Abstract Cyclic voltammetry was used to investigate the electrochemical reduction of nitrophenol isomers at a glassy carbon electrode modified with carbon nanotubes, and a derivative voltammetric technique was adopted to improve the resolution and enhance the determination sensitivity. In 0.1 mol L−1 HAc–NaAc buffer solution (pH 5.0), the modified electrode showed a good electrocatalytic response towards nitrophenol isomers. Through a derivative technique, the peak currents increased significantly and the reduction peaks of nitrophenol isomers could be separated, so the method could be applied to direct simultaneous determination without preseparation. The linear calibration ranges were 4.0 × 10−6 to 2.0 × 10−3 mol L−1 for o-nitrophenol, 1.0 × 10−5 to 1.0 × 10−3 mol L−1 for m-nitrophenol and 2 × 10−6 to 4.0 × 10−3 mol L−1 for p-nitrophenol, with detection limits of 5.0 × 10−7, 6.0 × 10−6 and 4.0 × 10−7 mol L−1, respectively.

Enhancement of surfactants in the electrochemical determination of phenols and the mechanisms research

The electrochemical responses of phenols can be enhanced effectively by using surfactants at the glassy carbon electrode. The enhancement of surfactant, including cetyl trimethyl ammonium bromide and cetyl pyridinium chloride, on trinitrophenol, 2,4-dinitrophenol, 2,5-dinitrophenol, o-dihydroxy-benzene, p-dihydroxy-benzene, 1-naphthol, 2-naphthol and triphenol has been investigated in HAc–NaAc buffer solution, and most of the results are reported first. The interaction mechanism among the electrode, surfactant and detected phenols was studied comprehensively and two mechanism models were suggested. One is electrostatic effect model and the other is hydrogen bond model. The optimal conditions, such as pH value, concentration of surfactant used, were also studied in detail. For ionized phenols, the optimal concentration of surfactant added was 1.0 × 10 −4 mol L −1, which was well below the critical micelle concentration. For nonionized phenols, the respective value was 1.2 × 10 −3 mol L −1, which was close to the critical micelle concentration. All of the results obtained will be of great significance to the determination of phenols and substituted phenols.

Nanosilver resonance scattering spectral method for determination of hydroxyl radical and its application

Silver nanoparticles were prepared under a microwave high-pressure condition using citric acid sodium as a reducer while the excess citrate was removed under high speed centrifugation. There is a resonance scattering (RS) peak at 470 nm for silver nanoparticles. In a pH 4.0 HAc-NaAc buffer solution, hydroxyl radicals from the Fenton reaction can oxidize silver nanoparticles to Ag+, resulting in the RS intensity decreasing. The decreased RS intensity at 470 nm (ΔI 470 nm) is linear with respect to the concentration of H2O2 (C) in the range of 0.27–7.56 μmol/L with a detection limit of 0.23 μmol/L. Its regression equation is ΔI 470 nm = 24.3 C + 13.8 with a correlation coefficient of 0.9959. This method was applied to screening the antioxidants with satisfactory results.

Effects of interaction of folic acid with uranium (VI) and basic triphenylmethane dyes on resonance Rayleigh scattering spectra and their analytical applications

In pH 4.2–4.8 HAc–NaAc buffer solution, folic acid (FA) could react with uranium (VI) to form a 2:1 anionic chelate which further reacted with some basic triphenylmethane dyes (BTPMD) such as Ethyl Violet (EV), Methyl Violet (MV) and Crystal Violet (CV) to form 1:2 ion-association complexes. As a result, not only the absorption spectra were changed, but also the intensities of resonance Rayleigh scattering (RRS) were enhanced greatly and the new RRS spectra were observed. The maximum RRS wavelengths were located at 328 nm for EV system, 325 nm for MV system and 328 nm for CV system. The fading degree (Δ A) and RRS intensities (Δ I) of three systems were different. Under given conditions, the Δ A and Δ I were all directly proportional to the concentration of FA. The linear ranges and the detection limits of RRS methods were 0.0039–5.0 μg mL −1 and 1.2 ng mL −1 for EV system, 0.0073–4.0 μg mL −1 and 2.2 ng mL −1 for MV system, 0.014–3.5 μg mL −1 and 4.7 ng mL −1 for CV system. The RRS methods exhibited higher sensitivity, so they are more suitable for the determination of trace FA. The optimum conditions, the influencing factors and the effects of coexisting substances on the reaction were investigated. The method can be applied to the determination of FA in serum and urine samples with satisfactory results. The structure of the ternary ion-association complex and the reaction mechanism were discussed in this work.

<i>In Vitro</i> Dissolution Behavior of Biphasic Tricalcium Phosphate Composite Powders Composed of α-Tricalcium Phosphate and β-Tricalcium Phosphate

Biphasic tricalcium phosphate (BTCP) powders composed of α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP) were prepared using amorphous calcium phosphate (ACP) precursor after heat treatment at 800oC. The in vitro dissolution behavior of the powders was examined after soaked in 0.1M NaAc-HAc buffer solution for different times. It was revealed that the Ca2+ and PO4 3- concentration, and pH value of the BTCP-soaked solution are higher than those of the α-TCP- and β-TCP-soaked solutions. The dissolution behavior of BTCP powders was explained. The specific dissolution behavior of BTCP powders can widen the biodegradation range of calcium phosphate family.

Spectrofluorometric study on the inclusion behavior of p-( p-carboxyl benzeneazo) calix[4]arene with norfloxacin

Spectrofluorometric titrations have been performed to investigate the inclusion behavior of p-( p-carboxyl benzeneazo) calix[4]arene (CBC4A) with norfloxacin (NFLX) in NaAc–HAc buffer solution (pH = 5.0). It was found that the fluorescence intensity of NFLX quenched regularly upon the addition of CBC4A. The results indicated 1:1 complex stoichiometry and an association constant of 8.21 × 10 5 L mol −1 at 20.0 °C were calculated by applying a deduced equation. Job's plot also verified the existence of 1:1 inclusion complex. The proposed interaction mechanism indicates that NFLX goes into (or partially goes into) the cavity of CBC4A with the help of hydrogen bonding and other forces. The various factors (pH value, ionic strength, and surfactants) affecting the inclusion process were examined in details.

Morphological and Structural Evolution of Mesoporous Silicas in a Mild Buffer Solution and Lysozyme Adsorption

Mesoporous silicas with various morphologies and structures were synthesized with the aid of 2,2,4-trimethylpentane (TMP) in the presence of nonionic surfactant P123 [(EO)20(PO)70(EO)20] as a structure-directing agent under mild reaction conditions (HAc-NaAc buffer solution, pH 4.4). The ropelike particles formed by end-to-end interconnected nanorods were obtained at a TMP/P123 weight ratio of 0.5. It is noteworthy to mention that the mesoporous nanorods have channels running parallel to the short axis. The silica hollow spheres can be obtained at a higher TMP/P123 weight ratio because of the fusion of the primary nanorods around the interface of the O/W emulsion. Initial synthesis temperatures of 15, 25, and 40 degrees C can lead to mesoporous silicas with highly ordered 2D hexagonal mesostructure, vesicular mesostructure, and mesostructured cellular foams (MCF), respectively. The mesoporous silicas exhibit high adsorption capacity (up to 536 mg g(-1)) and very rapid (<5 min to reach equilibrium) lysozyme immobilization. More importantly, it is revealed that mesoporous silica hollow spheres with rugged surfaces can greatly accelerate the adsorption rate of the enzyme during the adsorption process.

A New Spectrofluorimetric Method for Determination of Trace Amounts 5-Hydroxytryptamine in Human Urine and Serum

A new spectrofluorimetric method was developed for the determination of trace amount of 5-hydroxytryptamine (5-HT) in human urine and serum samples. In the NaAc-HAc buffer solution of pH=5.80, 5-HT can react with formaldehyde-acetylacetone system to form a new compound which sends yellow green fluorescence at 533 nm and the enhanced fluorescence intensity is in proportion to the concentration of 5-HT. Optimum conditions for the determination of 5-HT were also investigated. The dynamic range and detection limit for the determination of 5-HT are 5.35 x 10(-7) approximately 1.07 x 10(-4) mol/L and 2.08 x 10(-7) mol/L, respectively. The developed method is simple, practical and can be successfully applied to determination of 5-HT in human urine and serum samples. Moreover, the enhancement mechanisms of the fluorescence intensity in the 5-HT - formaldehyde-acetylacetone system have been also discussed.