Adsorption of Cu(II), Cd(II), Pb(II), Cr(VI) by double hydroxides on the basis of Al oxide and Zr, Sn, and Ti oxides

It was studied the equilibrium adsorption and adsorption kinetics of Cu(II), Cd(II), Pb(II), and Cr(VI) by composite hydroxides formed by Me _x O _y · nH₂O and Me_0.4–0.7Al_0.6–0.3O _y · nH₂O, where Me = Zr, Sn and Ti. It was estimated the values of the diffusion coefficients of adsorbed ions Cu(II) and Cr(VI) from kinetic values. It was established that the estimated diffusion coefficients of adsorbed ions Cu(II) are in the range 0.4 × 10⁻¹²–2.5 × 10⁻¹² m²/s for individual hydroxides and 1.2 × 10⁻¹²–2.8 × 10⁻¹² m²/s for double hydroxides. The obtained values of diffusion coefficients Cr (VI) for double hydroxides are 0.1 × 10⁻¹⁰–0.4 × 10⁻¹⁰ m²/s.     

Study and Application of Electrochemical Behavior of Calcium-ARS on a Mercury Film Electrode

A sensitive complex absorptive wave of Ca-ARS was obtained by using differential pulse voltammetry when a mercury film glass carbon electrode was immersed in 0.1 mol L⁻¹ KOH and 4.5×10⁻⁴ mol L⁻¹ ARS solution. The peak potential obtained was −1.17 V (vs Ag-AgCl). The peak current was proportional to the concentration of calcium in the range of 5.0×10⁻⁸−4.2×10⁻⁵ mol L⁻¹. The detection limit was 2.0×10⁻⁸ mol L⁻¹. This method was applied successfully to determining traces of calcium in blood serum. The electrochemical behavior of the system was also studied by cyclic voltammetry, and the experiment results showed that the electrode process was an irreversible absorptive with two electrons participating. Translated from Journal of Beijing Normal University (Natural Science Edition), 2005, 41(2) (in Chinese)     

Study of adsorption kinetics for fluorescent whitening agent on fiber surfaces

Adsorption kinetics for a stilbene derivative type fluorescent whitening agent (FWA) on fiber surfaces was studied based on a real-time spectroscopic measurement system. Results showed that the time-dependent behavior of FWA agrees to that of a mono-molecular adsorption layer on fiber surfaces,as characterized in Langmuir-type expression. The adsorption has two distinguishable stages includ-ing initial fast phase with the primary constant of 1.51×1014 and the later near-equilibrium phase with the secondary constant of 4.96×10-4. The maximum amount of FWA adsorbed on fiber surfaces is 1.67×10-4g (per dry weight based fiber) in the initial phase. A mathematical model of adsorption kinetics was therefore established and evaluated. This model is important for the optimization of FWA applica-tion in papermaking.     

Naked eye detection of cadmium using inorganic–organic hybrid mesoporous material

A novel and low-cost optical sensor for the naked eye detection of Cd²⁺in aqueous media based on mesoporous silica containing 4-(2-pyridylazo)resorcinol (PAR) as a probe molecule anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC) was prepared. The effects of various factors such as pH, solvent volume, temperature, reaction time, amount of the material, and the presence of various ions were studied in order to optimize operating conditions. The detection was based on the color change of PAR from orange-yellow to purple as a result of complexation with Cd²⁺. The intensity of the Cd-PAR complex varies linearly with the Cd²⁺concentration, from zero to 1.78×10⁻⁷ mol dm⁻³. The detection and quantification limits for the method when determining Cd²⁺ were 1.75×10⁻⁸ and 5.77×10⁻⁸ mol dm⁻³, respectively, with a correlation coefficient of 0.99. Good chemical stability of the material was observed for a period of five months. The developed sensor was applied to the analysis of various industrial effluents and tap water samples. Electronic supplementary material Supplementary material is available for this article at     

Preconcentration and Voltammetric Determination of the Antihypertensive Doxazosin on a C8 Modified Carbon Paste Electrode

 An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques has been carried out. The process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V in citric acid-citrate buffer (pH 3.0). A mechanism based on the oxidation of the amine group is postulated. Two methods based on adsorptive stripping (AdS) of doxazosin at the C₈-modified carbon paste electrode (C₈-MCPE), before its voltammetric determination, are studied, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. By means of AdS-DPV and C₈-MCPE, doxazosin can be determined over the 1.0 × 10⁻⁹ to 3.0 × 10⁻⁸ mol L⁻¹ range with a variation coefficient of 2.2% (2.0 × 10⁻⁸ mol L⁻¹) and a limit of detection of 7.4 ×10⁻¹⁰ mol L⁻¹. If AdS-SWV is used, a linear range from 1.0 × 10⁻⁹ to 4.0 × 10⁻⁸ mol L⁻¹ is obtained, the variation coefficient being 2.8% (2.0 × 10⁻⁸ mol L⁻¹, and the limit of detection reached 7.7 × 10⁻¹⁰ mol L⁻¹. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations. Received March 13, 1999. Revision December 23, 1999.     

Preparation of silver nanoparticles in aqueous solutions in the presence of carbonate ions as stabilizers

Silver nanoparticles are prepared by reducing Ag⁺ ions with sodium borohydride in aqueous solutions containing carbonate ions (5 × 10⁻⁵−1 × 10⁻² mol l⁻¹). It is established that carbonate ions represent an efficient stabilizer that provides nanoparticles with electrostatic protection via the formation of an electrical double layer. The maximum stability of a silver dispersion is observed at a carbonate ion concentration of 1 × 10⁻³ mol l⁻¹. The average size of silver nanoparticles is 10.0 ± 2.5 nm. The formation kinetics of silver nanoparticles is described by an equation for a first-order reaction with a rate constant of 2.3 × 10⁻³ s⁻¹ (±20%).     

Electrochemical behavior of electrodeposited film derived from rhein and its activity towards myoglobin reduction

The stable electroactive thin film of rhein has been investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical impedance spectroscopy of the electrodeposited film derived from rhein indicated the electrode reaction was kinetically controlled in the region of higher frequency, the charge transfer resistance was 2.6×10³ Ω cm² and capacitance value was 13.2 μF cm² . The electrodeposited film derived from rhein exhibited a good electrocatalytic activity for myoglobin (Mb) reduction. In 0.30 mol dm⁻³ H₂SO₄solution, the catalysis currents were proportional to the concentrations of Mb over the range of 1.5×10⁻⁷–1.3×10⁻⁵ mol dm⁻³. The detection limit is 1.0×10⁻⁷ mol dm⁻³ (S/N=3). The relative standard deviation is 4.8% for eight successive determinations of 5.0×10⁻⁷ mol dm⁻³ Mb.     

Fluorescent microscopic determination of gatifloxacin in milk,injection, human urine,and rabbit serum samples by self-ordered ring technique on glass slides support

A simple and sensitive self-ordered ring (SOR) technique, which was based on the capillary effect of solvent on a hydrophobic glass slide, was successfully applied to the determination of gatifloxacin in milk, injection, human urine and rabbit serum samples. In a medium of pH 3.20 (HAc-NaAc) with the aid of poly(vinyl alcohol)-124 (PVA-124), when 0.50 μL aluminum-sensitized gatifloxacin was dropped on glass slide with dimethyl dichlorosilane (DMCS) pretreated, a typical fluorescent SOR with diameter (2R) of the ring less than ca. 1.77 mm and the belt width (2δ) less than 29.3 μm can be obtained. The solute on the ring belt had strong fluorescence. Data of the imaged SOR showed that the gatifloxacin molecule across the SOR belt section follows a Gaussian distribution. The assay showed that when the droplet volume is 0.1 μL, the SOR method could be used to determine gatifloxacin in the range of 5.61 × 10⁻¹⁴ ∼ 1.50 × 10⁻¹² mol/ring (5.61 × 10⁻⁸∼1.50 × 10⁻⁵ M) and the limit of determination (LOD) reached 5.61 × 10⁻¹⁵ mol/ring (5.61 × 10⁻⁸ M) with three-fold signal-to-noise ratio (S/N = 3).     

Adsorptive anodic stripping voltammetry of zirconium(IV)-alizarin red S complex at a carbon paste electrode

A sensitive adsorptive anodic stripping procedure for the determination of trace zirconium at a carbon paste electrode (CPE) has been developed. The method is based on adsorptive accumulation of the Zr(IV)-alizarin red S(ARS) complex onto the surface of the CPE, followed by oxidation of adsorbed species. The optimal experimental conditions include the use of 0.10 mol · L⁻¹ ammonium acetate buffer (pH 4.3), ARS, an accumulation potential of 0.20 V (versus SCE), an accumulation time of 2 min, a scan rate of 200 mV · s⁻¹ and a second-order derivative linear scan mode. The oxidation peak for the complex appears at 0.69 V. The peak current is proportional to the concentration of Zr(IV) over the range of 1.0 × 10⁻⁹–2.0 × 10⁻⁷ mol · L⁻¹, and the detection limit is 3 × 10⁻¹⁰ mol · L⁻¹ for a 2 min adsorption time. The relative standard deviations (n = 8) for 5.0 × 10⁻⁸ and 5.0 × 10⁻⁹ mol · L⁻¹ Zr(IV) are 3.3 and 4.8%, respectively. The proposed method was applied to the determination of zirconium in ore samples with satisfactory results.     

Synthesis, characterization and studies on the third-order optical non-linearities of novel charge-transfer heteropoly complexes (C8H12N2)5H7PMo12O40 and (C8H12N2)3H3PMo12O40·5H2O

Summary Two novel charge-transfer (CT) heteropoly complexes, (C₈H₁₂N₂)₅H₇PMo₁₂O₄₀ (1) and (C₈H₁₂N₂)₃H₃-PMo₁₂O₄₀·5H₂O (2), prepared by reacting p-Me₂NC₆H₄NH₂ with the four-electron heteropoly blue H₇PMo₁₂O₄₀·12H₂O and heteropoly acid H₃PMo₁₂O₄₀· xH₂O, respectively, were characterized by elemental analysis, and u.v., i.r., XPS and e.s.r. spectroscopies. A sizable electron-transfer interaction occurs within the product molecules and the heteropoly anions retain their Keggin structure. Their third-order optical non-linearity coefficients were measured using the Z-scan technique at a concentration of 4.68 × 10⁻⁶ mol dm⁻³ for (1) and 2.79 × 10⁻⁶ mol dm⁻³ for (2), with I ₀ = 2.38 × 10¹³ w m⁻² and λ = 532nm. The |χ⁽³⁾| for (1) is 2.61 × 10⁻¹⁰ esu and |χ⁽³⁾| for (2) is 1.05 × 10⁻¹⁰ esu.     

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, E _D, ΔS _rc and ΔH _rc 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 I _p(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%.     

Simultaneous determination of catechol and hydroquinone based on poly (diallyldimethylammonium chloride) functionalized graphene-modified glassy carbon electrode

Simultaneous determination of catechol (CC) and hydroquinone (HQ) were investigated by voltammetry based on glassy carbon electrode (GCE) modified by poly (diallyldimethylammonium chloride) (PDDA) functionalized graphene (PDDA-G). The modified electrode showed excellent sensitivity and selectivity properties for the two dihydroxybenzene isomers. In 0.1 mol/L phosphate buffer solution (PBS, pH 7.0), the oxidation peak potential difference between CC and HQ was 108 mV, and the peaks on the PDDA-G/GCE were three times as high as the ones on graphene-modified glass carbon electrode. Under optimized conditions, the PDDA-G/GCE showed wide linear behaviors in the range of 1 × 10⁻⁶−4 × 10⁻⁴ mol/L for CC and 1 × 10⁻⁶−5 × 10⁻⁴ mol/L for HQ, with the detection limits 2.0 × 10⁻⁷ mol/L for CC and 2.5 × 10⁻⁷ mol/L for HQ (S/N = 3) in mixture, respectively. Some kinetic parameters, such as the electron transfer number (n), charge transfer coefficient (α), and the apparent heterogeneous electron transfer rate constant (k _s), were calculated. The proposed method was applied to simultaneous determine CC and HQ in real water samples of Yellow River with satisfactory results.     

Electrochemical behaviors of metol on ionic-liquid-modified carbon paste electrode and its analytical application

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k _s) as 4.02 × 10⁻³ s⁻¹, and the diffusion coefficient (D) as 6.35 × 10⁻⁵ cm²/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10⁻⁶ ∼ 1.0 × 10⁻³ mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10⁻⁶ mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.     

Adsorption studies of cesium on a new inorganic exchanger ammonium molybdophosphate-alumina (AMP-Al2O3)

The applicability of ammonium molybdophosphate-alumina (AMP-Al₂O₃) for the efficient removal of Cs from aqueous solution by adsorption has been investigated. The kinetics of adsorption of cesium ions has been studied by using radioanalytical procedure over a concentration range of 10⁻⁴−10⁻² mol.dm⁻³ and in the temperature range of 303–318 K. The results showed that the uptake follows the first order rate law with respect to cesium concentration and obeys Langmuir and modified Freundlich adsorption isotherm in the concentration range studied. Equilibrium adsorption values at different temperatures have been utilised to evaluate change in standard thermodynamic parameters (ΔH ⁰, ΔG ⁰ and ΔS ⁰). From the thermodynamic parameters it is found that the process is exothermic in nature.     

A Novel Enhancing Flow-Injection Chemiluminescence Method for the Determination of Glutathione Using the Reaction of Luminol with Hydrogen Peroxide

 A rapid flow-injection method with chemiluminescence (CL) detection is described for the determination of glutathione (GSH). The method is based on the CL reaction of luminol and hydrogen peroxide. GSH can greatly enhance the chemiluminescence intensity in 0.1 mol/L borax–sodium hydroxide buffer solution (pH = 9.7). The maximum CL intensity was directly proportional to the concentration of GSH in the range 3.0 × 10⁻⁷–2.0 × 10⁻⁵ mol/L, and the detection limit was 6.8 × 10⁻⁸ mol/L. The relative standard deviation was 3.4% for 5.0 × 10⁻⁶ mol/L of GSH (n = 11). Received October 23, 2001; accepted June 18, 2002     

Anode oxidation of copper in alkali media in the presence of glycine, α-alanine,and asparagine acid

The effect of glycine, α-alanine, and asparagine acid on the kinetics of anode processes occurring for copper in alkali electrolytes is studied. The experiments are performed in a background solution of 1 × 10⁻² M NaOH (pH 12). The concentrations of glycine and α-alanine are varied in the range of 1 × 10⁻⁶-1 × 10⁻¹ M, and the concentration of asparagine acid is varied in the range of 1 × 10⁻⁵-1 × 10⁻³ M. All amino acids used in this work have been found to stimulate anode oxidation of passivated copper, initiating local activation (LA) of the metal. Depending on the nature of amino acids, this effect occurs in various concentration ranges: for glycine and α-alanine, it takes place at c= 5 × 10⁻³-2 × 10⁻² M, while for asparagine acid, at c = 1 × 10⁻⁵−1 × 10⁻³ M. In addition to this general regularity, several individual peculiarities have been revealed: in the systems containing a monobasic amino acid additive, local activation occurs at E = 0.10–0.20 V, while in the presence of a dibasic amino acid, the local activation is observed at two potentials, E _LA¹ = 0.20–0.30 V and = E _LA² = 0.80–0.90 V, separated by the repassivation region.     

Chemiluminescence mechanisms of cerium-norfloxacin and its application in urine analysis

In this article, novel chemiluminescence mechanisms between norfloxacin and cerium(IV) in an acidic medium were studied. Chemiluminescence spectra of the present system were recorded observing three maximum emissions at about 475 nm, 550 nm, and 620 nm, respectively. The results indicate that the chemiluminescence peaks located at 475 nm and 620 nm can be ascribed to the emission of a singlet oxygen, while the chemiluminescence emission at 550 nm occurred in course of the reaction between acidic cerium(IV) and the phenolic intermediate. Under optimum conditions, the chemiluminescence intensity was linear with the concentration of norfloxacin over the range of 2.0 × 10⁻⁸−1.0 × 10⁻⁵ g mL⁻¹ and the detection limit of 1.0 × 10⁻⁸ g mL⁻¹ (S/N = 3). The relative standard deviation was 1.94 % for a 4.0 × 10⁻⁷ g mL⁻¹ norfloxacin solution considering eleven repeated measurements. The present chemiluminescence system was successfully applied in the determination of norfloxacin in pharmaceutical preparations and concentration-time profiles in urine.     

Square-wave adsorptive stripping voltammetric determination of an antihistamine drug astemizole

The square-wave voltammetric technique was used to explore the adsorption properties of the astemizole drug. The analytical methodology used was based on the adsorptive preconcentration of the drug on a hanging mercury drop electrode (HMDE), followed by the electrochemical reduction process which yielded a well-defined cathodic peak at −1.184 V (vs. the Ag/AgCl electrode). To achieve high sensitivity, various experimental and instrumental variables were investigated such as the supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, SW frequency, pulse amplitude, convection rate, and the working electrode area. Under the optimized conditions, the AdSV peak current was proportional over the analyte concentration range of 5 × 10⁻⁷ to 2.5 × 10⁻⁶ mol L⁻¹ (r = 0.998) with the detection limit of 1.4 × 10⁻⁸ mol L⁻¹ (6.4 ng mL⁻¹). The precision of the proposed method in terms of RSD was 2.4 %, whereas the method accuracy was indicated by the mean recovery of 100.1 %. Possible interferences of several substances usually present in the pharmaceutical tablets and formulations were also evaluated. The applicability of this electroanalytic approach was illustrated by the determination of astemizole in tablets and biological fluids.     

Microgravity experiments on colloidal crystallization of silica spheres in the presence of sodium chloride

 Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10⁻⁶ mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10⁻⁶ and 4 × 10⁻⁶ mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important for retardation in microgravity. Received: 20 January 2000 Accepted: 9 March 2000     

Voltammetric detection of paraquat pesticide on a phthalocyanine-based pyrolitic graphite electrode

This work describes the application of an ordinary pyrolitic graphite electrode modified by metallophthalocyanine allied to square wave voltammetry for the study of the electrochemical behavior of the herbicide paraquat and the development of a method for its analytical determination in natural water samples. Preliminary experiments indicated that the best responses, considering the intensities of the current and voltammetric profile for the paraquat reduction process, were obtained when the electrode modified by cobalt phthalocyanine was employed, which had a better catalytic activity as a result of this modification compared with that for an unmodified electrode and electrodes modified by iron, manganese and the acid form of the phthalocyanines. Studies of the concentration of cobalt phthalocyanine and the adsorption time showed that 1.0 × 10⁻⁴ mol L⁻¹ cobalt phthalocyanine with an adsorption time of 10 min was sufficient to obtain reliability and stability of modification for employment in the development of the electroanalytical procedure for paraquat determination in natural water samples. The variation in pH of a 0.10 mol L⁻¹ Britton–Robinson buffer solution and the square wave parameters indicated that the best conditions to reduce paraquat were pH 7.0, a frequency of 100 s⁻¹, a scan increment of 2 mV and a square wave amplitude of 50 mV. Under such conditions, the variation of paraquat concentrations from 5.00 × 10⁻⁷ to 2.91 × 10⁻⁵ mol L⁻¹ showed a linear relation, with detection and quantification limits of 26.53 and 88.23 μg L⁻¹; those values were lower than the maximum limits for drinking water permitted by the Brazilian Environmental Council (100 μg L⁻¹), indicating that the method could be employed to analyze paraquat in drinking water samples.