Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine

A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with a detection limit of 4.0 × 10⁻⁷ M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10⁻⁵ M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry. The text was submitted by the authors in English.     

Determination of ultramicroquantities of Au(III) by its catalytic effect on 4-hydroxyl coumarone oxidation with potassium permanganate

A simple and fast kinetic method is based on the oxidation of 4-OH coumarone using KMnO₄ and the determination of ultramicroamounts of Au(III) by its catalytic effect on this reaction. The sensitivity of the method is 25 ng/mL. The relative error ranges between 9.20–3.90% for the concentration interval 5 × 10⁻⁸–2 × 10⁻⁷ g/mL. The selectivity of the method is very good, and the effect of foreign ions is investigated. The proposed approach has been applied to the determination of traces of Au(III) in copper ore. The text was submitted by the authors in English.     

Voltammetric determination of trace amounts of gold(III) with a carbon paste electrode modified with chelating resin

A carbon paste electrode modified with chelating resin (ammino-isopropylmercaptan-type cross-linked chelating resins) for the voltammetric determination of gold(III) was characterized by cyclic voltammetry. The gold(III) ion is accumulated on the surface of the modified electrode only by the chelating effect of the modifier in the carbon paste, without application of a potential. After exchange of the medium the accumulated amount of gold(III) is determined by voltammetry in a blank electrolyte solution. The response depends on both the concentration of gold and the accumulation time. For a 5-min preconcentration time, a linear calibration graph was obtained in the range 3 × 10^?8-1 × 10^?6 M and the detection limit was about 1 × 10^?8 M. A combination of chemical and electrochemical renewal allows the use of a single modified electrode in multiple analytical determinations over several days. For ten preconcentration—determination—renewal cycles [2 × 10^?7 M Au(III)], the response could be reproduced with 4.7% relative standard deviation. Many parameters such as the composition of the paste and pH influence the response of the measurement. Many other metal ions have no or little effect on the determination of gold. The procedure was applied to the determination of gold in minerals, copper and anode mud, with good results.     

Determination of hemoglobin at a novel NH2/ITO ion implantation modified electrode

A novel electrode was prepared by implanting NH₂ ⁺ into an ITO film (NH₂/ITO). Gold nanoparticles were deposited on the surface of NH₂/ITO electrode. The NH₂/ITO and Au/NH₂/ITO electrodes were used to determine hemoglobin (Hb) immobilized on the electrodes surfaces. The relationship of the reductive peak current value of Hb among different electrodes was: Hb/ITO:Hb/Au/ITO:Hb/NH₂/ITO:Hb/Au/NH₂/ITO=1:1.5:2:4. The linkage between the –NH₂ implanted into ITO film and the –COOH of Hb was recognized to be the reason for the increase of active Hb coverage on NH₂/ITO electrode compared with the ITO electrode. Increase of active Hb coverage on Au/NH₂/ITO compared with Au/ITO was attributed to the different amount of gold nanoparticles deposited. The determination of Hb at an Au/NH₂/ITO electrode was optimized. Calibration curve was obtained over the range of 1.0 × 10⁻⁸ – 1.0 × 10⁻⁶ mol · L⁻¹ with a detection limit of 1.0 × 10⁻⁸ mol · L⁻¹. Results showed that the novel NH₂/ITO and Au/NH₂/ITO electrodes exhibited good stability, reproducibility besides better electrochemical performance. Correspondence: Jing Bo Hu, Department of Chemistry, Beijing Normal University, Beijing 100875, China     

New adsorptive square wave method for trace determination of prilocain in the flow injection system by a fast fourier analysis

The determination of prilocain, used to manage tonic-clonic seizures, has been carried out at micro gold electrode (Au UME) using continuous fast Fourier transform square wave voltammetry. The Au UME electrode exhibited an effective response towards prilocaine adsorption. The peak current was also found to be significantly increased. The determination was carried out in phosphate containing electrolyte in the pH of 2.0 and a well-defined change on the peak current were noticed. The peak current was found to be linearly dependent on concentration of prilocain in the concentration range 5.0 × 10⁻⁷–1.0 × 10⁻¹¹ M with a detection limit of 5.0 × 10⁻¹² M. This paper describes development of a new analysis system to determine of prilocain by a novel square wave voltammetry method to perform a very sensitive method. The method used for determination of prilocain by measuring the changes in admittance voltammogram of a gold ultramicroelectrode (in 0.05 M H₃PO₄ solution) caused by adsorption of the prilocain on the electrode surface. Variation of admittance in the detection process is created by inhibition of oxidation reaction of the electrode surface, by adsorbed of prilocain. Furthermore, signal-to-noise ratio has significantly increased by application of discrete Fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some parameters such as SW frequency, eluent pH, and accumulation time were optimized. The relative standard deviation at concentration 5.0 × 10⁻⁸ M is 5.8% for 5 reported measurements.     

Enzyme biosensor based on the immobilization of HRP on SiO<Subscript>2</Subscript>/BSA/Au composite nanoparticles

In this work, an enzyme biosensor based on the immobilization of horseradish peroxidase (HRP) on SiO₂/BSA/Au/thionine/nafion-modified gold electrode was fabricated successfully. Firstly, nafion was dropped on the surface of the gold electrode to form a nafion film followed by chemisorption of thionine (Thi) as an electron mediator via the ion-exchange interaction between the Thi and nafion. Subsequently, the SiO₂/BSA/Au composite nanoparticles were assembled onto Thi film through the covalent bounding with the amino groups of Thi. Finally, HRP was immobilized on the SiO₂/BSA/Au composite nanoparticles due to the covalent conjugation to construct an enzyme biosensor. The surface topographies of the SiO₂/BSA/Au composite nanoparticles were investigated by using scanning electronic microscopy. The stepwise self-assemble procedure of the biosensor was further characterized by means of cyclic voltammetry and chronoamperometry. The enzyme biosensor showed high sensitivity, good stability and selectivity, a wide linear response to hydrogen peroxide (H₂O₂) in the range of 8.0 × 10^-6 ∼ 3.72 × 10^-3 mol/L, with a detection limit of 2.0 × 10^-6 mol/L. The Michaelies-Menten constant K_M^app K_M^{app} value was estimated to be 2.3 mM.     

Sensitive and selective determination of mercury by differential pulse stripping voltammetry after accumulation of mercury vapour on a gold plated graphite electrode

 A selective and sensitive method is proposed for the determination of mercury by anodic stripping voltammetry after its preconcentration from the gas phase. Mercury from the sample solution is reduced to elemental Hg by SnCl₂ and volatilized by the bubbles of a carrier gas. The gas containing mercury vapour is dried and passed through a capillary onto a gold coated graphite electrode. An anodic stripping voltammogram is recorded from 0.1 mol/l HClO₄+3×10^-3 mol/l HCl solution. The calibration curve is linear from 1×10^-9 to 4×10^-8 mol/l Hg(NO₃)₂. The absolute detection limit is 0.46 ng Hg. The relative standard deviations for 4×10^-9 mol/l and 2×10^-8 mol/l Hg(NO₃)₂ are 9.8% and 6.1%, respectively (n=5). Received: 18 December 1995/Revised: 16 April 1996/Accepted: 20 April 1996     

Sensitive and selective determination of mercury by differential pulse stripping voltammetry after accumulation of mercury vapour on a gold plated graphite electrode

A selective and sensitive method is proposed for the determination of mercury by anodic stripping voltammetry after its preconcentration from the gas phase. Mercury from the sample solution is reduced to elemental Hg by SnCl₂ and volatilized by the bubbles of a carrier gas. The gas containing mercury vapour is dried and passed through a capillary onto a gold coated graphite electrode. An anodic stripping voltam-mogram is recorded from 0.1 mol/1 HClO₄ + 3 × 10⁻³ mol/1 HCl solution. The calibration curve is linear from 1 × 10⁻⁹ to 4 × 10⁻⁸ mol/1 Hg(NO₃)₂. The absolute detection limit is 0.46 ng Hg. The relative standard deviations for 4 × 10⁻⁹ mol/1 and 2 × 10⁻⁸ mol/1 Hg(NO₃)₂ are 9.8% and 6.1%, respectively n = 5).     

Catalytic adsorptive stripping voltammetric determination of copper(II) on a carbon paste electrode

A catalytic adsorptive stripping voltammetric method for the determination of copper(II) on a carbon paste electrode (PCE) in an alizarin red S (ARS)-K₂S₂O₈ system is proposed. In this method, copper(II) is effectively enriched by both the formation and adsorption of a copper(II)-ARS complex on the PCE, and is determined by catalytic stripping voltammetry. The catalytic enhancement of the cathodic stripping current of the Cu(II) in the complex results from a redox cycle consisting of electrochemical reduction of Cu(II) ion in the complex and subsequent chemical oxidation of the Cu(II) reduction product by persulfate, which reduces the contamination of the working electrode from Cu deposition and also improves analytical sensitivity. In Britton-Robinson buffer (pH 4.56±0.1) containing 3.6×10⁻⁵ mol L⁻¹ ARS and 1.6×10⁻³ mol L⁻¹ K₂S₂O₈, with 180 s of accumulation at −0.2 V, the second-order derivative peak current of the catalytic stripping wave was proportional to the copper(II) concentration in the range of 8.0×10⁻¹⁰ to ∼3.0×10⁻⁸ mol L⁻¹. The detection limit was 1.6×10⁻¹⁰ mol L⁻¹. The proposed method was evaluated by analyzing copper in water and soil.     

Selective method for the determination of gold by anodic stripping voltammetry

A highly selective method for the deter- mination of gold by anodic stripping voltammetry is described. For preconcentration a glassy carbon electrode, activated by deposition of small amounts of gold before the measurement, is proposed. The Au³⁺ reduction process at such an electrode is effective starting with the potential +0.4 V vs. Ag/AgCl electrode. A linear dependence of the current of the gold stripping peak on the gold concentration was obtained in the range from 5×10⁻⁸ to 1×10⁻⁶ mol/l. The relative standard deviation for 2×10^-7 mol/l HAuCl₄ was 4.2% (n=5). The detection limit was 4×10^-9 mol/l. The accuracy of the method was verified by the determination of gold in reference materials.     

Amperometric Hydrogen Peroxide Biosensor Based on the Immobilization of Horseradish Peroxidase (HRP) on the Layer‐by‐Layer Assembly Films of Gold Colloidal Nanoparticles and Toluidine Blue

The precursor film was first formed on the Au electrode surface based on the self‐assembly of L ‐cysteine and the adsorption of gold colloidal nanoparticles (nano‐Au). Layer‐by‐layer (LBL) assembly films of toluidine blue (TB) and nano‐Au were fabricated by alternately immersing the electrode with precursor film into the solution of toluidine blue and gold colloid. Cyclic voltammetry (CV) and quartz crystal microbalance (QCM) were adopted to monitor the regular growth of {TB/Au} bilayer films. The successful assembly of {TB/Au}_n films brings a new strategy for electrochemical devices to construct layer‐by‐layer assembly films of nanomaterials and low molecular weight materials. In this article, {TB/Au}_n films were used as model films to fabricate a mediated H₂O₂ biosensor based on horseradish peroxidase, which responded rapidly to H₂O₂ in the linear range from 1.5×10^?7 mol/L to 8.6×10^?3 mol/L with a detection limit of 7.0×10^?8 mol/L. Morphologies of the final assembly films were characterized with scanning probe microscopy (SPM).     

Chemical separation of enriched cadmium target from copper backing in cyclotron production of radioisotope 111In

A radiochemical purification procedure was developed for the separation of enriched cadmium (¹¹¹Cd and ¹¹²Cd) from natural copper that used as backing; and was based upon the chromatographic adsorption. The separation of copper from cadmium was studied in this work. The ions were selectively separated from aqueous solution. Ion-exchange chromatography was employed as a column (1.5 cm i.d. and 15 cm length) with AG1-X8 resin (chloride form, 100–200 mesh) and a flow rate of 1–2 ml/min throughout the separation. 6 M HCl media was used for the adsorption of Cd and Cu on the resin. Then, Cu was eluted by 2 M HCl and Cd by 100 ml 0.5 M HNO₃. The amount of Cu and Cd ions in the final solution (0.5 M HNO₃) were measured by pulse polarographic method and the concentration of Cu was found to be <0.1 ppm. The Cd was quantitatively recovered and the recovery yield from ion-exchange chromatography was greater than 96 %.     

The amperometric determination of indole-3-acetic acid based on CeCl<Subscript>3</Subscript>-DHP film modified gold electrode

An amperometric sensor for the determination of indole-3-acetic acid (IAA) based on the CeCl₃-DHP film modified gold electrode was developed. CeCl₃ was dissolved into water in the presence of dihexadecyl hydrogen phosphate (DHP). The IAA sensor was prepared via evaporating solvent of the CeCl₃-DHP dispersion on the gold electrode surface. The amperometric response of IAA on the CeCl₃-DHP film modified gold electrode was investigated. The experimental results indicate that the passivation of the electrode due to the adsorption of the oxidation product of IAA decreases significantly at the CeCl₃-DHP film modified gold electrode, in contrast to that at the bare and the DHP modified gold electrode. The experimental parameters were optimized and an electrochemical method for the determination of IAA was established. The oxidation peak current is linearly with the concentration of IAA from 1 × 10⁻⁷ to 2 × 10⁻⁵ mol l⁻¹ and the detection limit is 3 × 10⁻⁸ mol l⁻¹. The relative standard deviation of eight measurements is 3.2% for 5 × 10⁻⁷ mol l⁻¹ IAA. The IAA in plant leaves were extracted and determined by the IAA sensor.     

Determination of gold,palladium and copper by flame atomic absorption spectrometry after preconcentration on silica gel modified with 3-(2-aminoethylamino)propyl group

A preconcentration method of gold, palladium and copper based on the sorption of Au (III), Pd (II) and Cu (II) ions on a column packed with 3-(2-aminoethylamino)propyl bonded silica gel is described. The modified silica gel was synthesized and characterized by FT-IR and C, H, N elemental analysis. At column preconcentration, the effects of parameters such as pH, volume, flow rate, matrix constituents of solutions and type of eluent on preconcentration of gold, palladium and copper were studied. The recoveries of Au (III), Pd (II) and Cu (II) were 98.93±0.51, 98.81±0.36 and 99.21±0.42 % at 95 % confidence level, respectively. The detection limits (δ) of the elements were 0.032, 0.016 and 0.012 μg ml⁻¹, respectively. The preconcentration method was applied for determination of gold and palladium in certified reference material SARM 7B and copper in river and synthetic seawater by FAAS. Gold, palladium and copper were determined with relative error lower than 10 %.     

Quartz Crystal Microbalance for Selenite Sensing Based on Growth of Cadmium Selenite Crystals Immobilized on a Monolayer of Phosphorylated 11-Mercapto-1-Undecanol

 A quartz crystal microbalance (QCM) sensor for selenite ions in aqueous solution was constructed based on crystal formation of cadmium selenite, immobilized with a self-assembly monolayer (SAM) of phosphorylated 11-mercapto-1-undecanol (MUD) on a QCM gold electrode surface. The mass change caused by the selective adsorption of selenite ions on the cadmium selenite crystals at the solid/solution interface was detected by the QCM. The response (−ΔF) of the modified QCM oscillator increased with increasing selenite ion concentrations in sample solutions, ranging from 9.7×10⁻⁵ to 9.0×10⁻⁴ M at pH 7.4. The synthetic process of anchoring cadmium selenite crystals on the phosphorylated MUD organic film was also followed by using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The atomic concentrations measured by XPS confirmed the crystal growth of cadmium selenite on the phosphorylated MUD SAM at the QCM gold electrode surface. From the AFM images, changes in surface topographic features were followed: the MUD SAM and phosphorylated MUD on the QCM gold electrode had similar surface roughness; however the difference for the cadmium selenite film on the phosphorylated MUD SAM was clearly seen. The observed QCM frequency change of the modified QCM oscillator per unit time was found to be proportional to the square of the supersaturation of cadmium selenite, indicating the crystal growth of cadmium selenite at the solid/solution interface. The modified QCM oscillator exhibited selectively strong QCM response to SeO₃ ²⁻ ion. In contrast, the responses to tested interfering anions were almost negligible. The order of anion selectivities of the present modified QCM sensor was SeO₃ ²⁻≫CO₃ ²⁻>SeO²⁻ ₄, SO₄ ²⁻, Br⁻, I⁻, NO₃ ⁻. These selectivities were basically attributable to the differences in solubility products and solubilities for the salts of each anion with cadmium (II) ion. Received May 12, 1998. Revision December 29, 1998.     

Behavior of cadmium(II) in irradiated aqueous solutions

Behavior of cadmium(II) in aqueous solutions irradiated by accelerated electrons was studied. A concentration of 8.8 × 10⁻⁴ mol L⁻¹ of cadmium dissolved from Cd(NO₃)₂ requires dose of 15 kGy to be effectively removed from the system containing 1 × 10⁻² mol L⁻¹ of HCOOK as a scavenger of OH radicals. The positive effect of deaeration with N₂O or N₂ was observed in the range of lower doses. The addition of solid modifiers (bentonite, active carbon, zeolite, Cu₂O, NiO, TiO₂ and CuO) reduced the effectivity of radiation removal of cadmium. Product of irradiation is CdCO₃. On the contrary, in the system with cadmium dissolved from CdCl₂ radiation reduction takes place. Systems contained organic complexants (ethylene diamine tetraacetic acid–EDTA, citric acid) were also studied. The solutions of Cd(NO₃)₂ containing initial concentration 2.37 × 10⁻⁴ mol L⁻¹ of Cd^II were mixed with 3 × 10⁻⁴ mol L⁻¹ EDTA. In this system the efficient degradation proceeds up to 90% at a dose of 45 kGy with addition of 5 × 10⁻³ mol L⁻¹ carbonate (pH 10.5). The product of irradiation is CdCO₃. The presence of 1 × 10⁻² mol L⁻¹ of HCOOK in the solution is necessary for radiation removal of cadmium complexed with citric acid (1 × 10⁻³ mol L⁻¹) at pH 8. With increasing concentration of HCOOK (up to 5 × 10⁻² mol L⁻¹) decreases the pH value necessary for the radiation induced precipitation of cadmium. The best result was obtained in the system containing zeolite as a solid modifier.     

Preparation and evaluation of a functionalized polymer-coated silica based sorbent for metal ion separation

A silica based sorbent with an anion complexone polymer coating, [24]ane-N₆ macrocycle, was prepared. The chelation properties of this material were investigated by elemental analysis, infrared spectra and Voige’s method. The polymer-coated silica column (25– 40 μm, 100 × 4.6 mm i.d.) was employed for trace metal analyses. Oxalic acid, malonic acid, succinic acid, citric acid, phthalic acid and acetic acid were used as mobile phases. Their retention characteristics were elucidated. Oxalic acid was found to be the most effective eluent. With a mobile phase consisting of oxalic acid (25 mM) and sodium nitrate (25 mM) at pH 4.2, the separation of copper(II), cadmium(II), cobalt(II) and zinc(II) in sea water could be achieved. The identification of metal ions was performed at 510 nm using 4(2-pyridylazo)resorcinol (1 × 10^–4 M) as post column reagent. The limits of detection were 5 × 10^–7 M, 1 × 10^–5 M, 3 × 10^–5 M and 2 × 10^–6 M for copper(II), cadmium(II), cobalt(II) and zinc(II) based on three times the standard deviation of the response for the lowest concentration (n = 5) in the chromatogram with a sample volume of 50 μL. For evaluation of data reliability, oyster tissue (NIST SRM 1566 a) was studied with the proposed system. Received: 9 February 1998 / Revised: 15 May 1998 / Accepted: 16 June 1998     

Determination of human serum albumin using aurothiomalate as electroactive label

A new electroactive label has been used to monitor immunoassays in the determination of human serum albumin (HSA) using glassy-carbon electrodes as supports for the immunological reactions. The label was a gold(I) complex, sodium aurothiomalate, which was bound to rabbit IgG anti-human serum albumin (anti-HSA-Au). The HSA was adsorbed on the electrode surface and the immunological reaction with gold-labelled anti-HSA was then performed for one hour by non-competitive or competitive procedures. The gold(I) bound to the anti-HSA was electrodeposited in 0.1 mol L⁻¹ HCl at −1.00 V for 5 min then oxidised in 0.1 mol L⁻¹ H₂SO₄ solution at +1.40 V for 1 min. Silver electrodeposition at −0.14 V for 1 min followed by anodic stripping voltammetry were then performed in aqueous 1.0 mol L⁻¹ NH₃–2.0×10⁻⁴ mol L⁻¹ AgNO₃. For both non-competitive and competitive formats, calibration plots in the ranges 5.0×10⁻¹⁰ to 1.0×10⁻⁸ mol L⁻¹ and 1.0×10⁻¹⁰ to 1.0×10⁻⁹ mol L⁻¹ HSA, respectively, with estimated detection limits of 1.5×10⁻¹⁰ mol L⁻¹ (10 ng mL⁻¹) and 1.0×10⁻¹⁰ mol L⁻¹ (7 ng mL⁻¹), respectively, were obtained. Levels of HSA in two healthy volunteer urine samples were also evaluated, using both immunoassay formats.     

Preparation of Polypyrrole/Nuclear Fast Red Films on Gold Electrode and Its Application on the Electrocatalytic Determination of Methyl‐dopa and Ascorbic Acid

A novel voltammetric method using the Ppyox/NFR/Au (poly pyrrole – nuclear fast red – gold) modified electrode was developed for simultaneous measurement of various combinations of ascorbic acid (AA) and methyldopa (MDA). Polypyrrole film was prepared by incorporation of nuclear fast red (NFR) as doping anion, during the electropolymerization of pyrrole onto a gold (Au) electrode in aqueous solution using cyclic voltammetric (CV) method, and then it was overoxidized at constant potential. Differential pulse voltammetry was utilized for the measurement of both analytes using modified electrode. Well‐separated voltammetric peaks were observed for ascorbic acid (AA) and methyldopa at the Ppyox/NFR/Au modified electrodes with peak separation of 0.210 V. It has been found that under optimum condition (pH 3.0), the oxidation of AA and MDA at the surface of the electrode occurs at a potential about 260 and 50 mV less positive than unmodified Au electrode respectively. The current catalytic oxidation peaks showed a linear dependent on the concentration of AA and MDA in the range of 9.0×10^?6 to 1.0×10^?3 and 1.0×10^?7 to 2.0×10^?5 mol L^?1 respectively. The detection limit of 5.8×10^?6 and 5.0×10^?8 mol L^?1 (S/N=3) were obtained for AA and MDA respectively. The modified electrode was used for determination of AA and MDA in some real samples such as human serum and tablet.     

Cold Deposition as a Novel Procedure for the Preparation of Titania Sol‐Gel: A Development of a High Sensitive Electrochemical Method for Determination of Cu(II) in the Presence of Arsenic(III)

Titania sol‐gel modified gold electrode (TSGMGE) was prepared with the usage of a new proposed cold deposition method at ?10 °C. Scanning electron microscope (SEM) operating at 30 kV was used to obtain micrographs of unmodified and modified electrodes. The obtained results showed that this procedure yields a sol‐gel with high porosity in comparison to conventional methods. The modified Au electrode was fabricated by trapping the L‐glutamine in titania sol‐gel at low temperatures to preparation of a new titania sol‐gel glutamine modified gold electrode (TSGGMGE). The possibility determination of traces of Cu(II) in the presence of As(III) was investigated using proposed electrode. Under the optimized conditions, copper was accumulated at ?0.35 V (vs. Ag/AgCl) for 40 s in 0.1 M acetate buffer (pH 4.0) in the presence of different amounts of arsenic. Two dynamic linear responses with good reproducibility were observed for copper ions in the concentration range of 1 × 10^?6 ?4 × 10^?4 M and 4 × 10^?8 ?6 × 10^?7 M.