Polarographic and voltammetric determination of trace amounts of 2-nitronaphthalene

The polarographic behaviour of 2-nitronaphthalene was investigated by DC tast polarography (DCTP) and differential pulse polarography (DPP), both at a dropping mercury electrode, and differential pulse voltammetry and adsorptive stripping voltammetry, both at a hanging mercury drop electrode. Optimum conditions have been found for the determination of 2-nitronaphthalene by the given methods in the concentration ranges of 2×10^–6–1×10^–4, 2×10^–7–1×10^–4, 1×10^–8–1×10^–4 and 2×10^–9–1×10^–8 M, respectively. Practical applicability of these techniques was demonstrated by the determination of 2-nitronaphthalene in drinking and river water after its preliminary separation and preconcentration using liquid–liquid and solid-phase extraction with limits of determination of 3×10^–10 M (drinking water) and 3×10^–9 M (river water).     

Copper film electrode for anodic stripping voltammetric determination of trace mercury and lead

A novel in-situ prepared copper film electrode (CuFE) for anodic stripping voltammetric measurement of trace levels of Hg(II) and Pb(II) is presented. The optimal electroanalytical performance of the CuFE was achieved in electrolyte solution comprising 0.1 M HCl and 0.4 M NaCl. The CuFE exhibited excellent operation in the presence of dissolved oxygen with calculated LoD of 0.1 μg L^− 1 Hg(II) and 0.06 μg L^− 1 Pb(II) in combination with 300 s accumulation time, repeatability with RSD of 4.5% for Hg(II) and 0.9% for Pb(II) (n = 12), and favourable linear response in the examined concentration range of 10–100 μg L^− 1 (R² = 0.997) for Hg and 5–70 μg L^− 1 (R² = 0.999) for Pb after 120 s accumulation. The electrode enabled also simultaneous detection of both investigated metal ions and revealed promising electroanalytical characteristics similar to or in certain cases surpassing those of commonly used gold electrodes.     

Carbon paste electrode based on surface activation for trace adriamycin determination by a preconcentration and voltammetric method.

A voltammetric determination of adriamycin (ADM) at a carbon paste electrode (CPE) in the presence of cetyltrimethylammonium bromide (CTAB) is described. ADM strongly adsorbs on the surface of the electrode by the adsorption of CTAB, thereby affecting the reduction current. This method provides a detection limit below 10(-10) mol/L for ADM. The experimental parameters, which influence the voltammetric responses of ADM, e.g. the pH value, variety and concentration of surfactants and the scan rate, were optimized. The reduction peak current changes linearly with the ADM concentration over the range from 2.5 x 10(-8) mol/L to 5 x 10(-6) mol/L. The detection limit is 4 x 10(-10) mol/L for an accumulation time of 3 min. The coefficient of variation, determined at 4 x 10(-6) mol/L ADM, is 3.0% (n = 8). Using this method, ADM in the patient's urine samples, which undergoes active ADM chemotherapy, was determined.     

Differential-pulse voltammetric determination of trace formaldehyde using magnetic microspheres and magnetic electrode

A new type of magnetic polymer microsphere containing acylhydrazine groups on the surface was synthesized. They can be reacted with formaldehyde to produce an electroactive adduct. Reduction of these derivatives following aggregation on a magnetic electrode is possible and is effective in the indirect determination of formaldehyde. The experimental conditions and electrode structure are discussed. Under the optimum conditions, it was found that the peak potential (Ep) of formaldehyde is -1.01 V (vs. Ag/AgCl). Formaldehyde in the range 1-1000 micrograms l-1 can be determined. The detection limit for formaldehyde is 0.3 microgram l-1 and the relative standard deviation for the determination of 100 micrograms l-1 formaldehyde was 2.26%. The method was applied to the determination of formaldehyde in environmental samples with satisfactory results.     

Novel membrane potentiometric sulfate ion sensor based on zinc-phthalocyanine for the quick determination of trace amounts of sulfate.

Poly(vinyl chloride) (PVC) based membranes of zinc-phthalocyanine (ZPC) with hexadecyltrimethylammonium bromide (HTAB) as a cation excluder, and dibutyl phthalate (DBP) and benzyl acetate (BA) as plasticizing solvent mediators were prepared and investigated as a SO4(2-) selective electrode. The best performance was observed with a membrane having a composition of ZPC-PVC-HTAB-BA in a ratio of 5%:32%:3%:60%, which works well over a wide concentration range (1.0 x 10(-2) - 1.0 x 10(-6) M) with a Nemstian slope of -29.2 mV per decade of activity, between the pH values of 2.0 to 7.0. This sensor shows a very fast response time of 10 s, and can be used over a period of 2 months with good reproducibility. The proposed sensor displays excellent selectivity for SO4(2-) over a large number of common inorganic anions. The sensor has been successfully applied for the direct and indirect determination of sulfate and zinc in zinc sulfate tablets, respectively. It was also used as an indicator electrode in the potentiometric titration of sulfate ions with barium ions.     

A new voltammetric sensor for the determination of sulfite in water and wastewater using modified-multiwall carbon nanotubes paste electrode

The electrochemical response of a modified-carbon nanotubes paste electrode with p-aminophenol was investigated as an electrochemical sensor for sulfite determination. The electrochemical behaviour of sulfite was studied at the surface of the modified electrode in aqueous media using cyclic voltammetry and square wave voltammetry. It has been found that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurs at a potential about 680?mV less positive than that of an unmodified-carbon nanotubes paste electrode. Under the optimized conditions, the electrocatalytic peak current showed linear relationship with sulfite concentration in the range of 2.0?×?10^?7–2.8?×?10^?4?mol?L^?1 with a detection limit of 9.0?×?10^?8?mol?L^?1 sulfite. The relative standard deviations for ten successive assays of 1.0 and 50.0?µmol?L^?1 sulfite were 2.5% and 2.1%, respectively. Finally, the modified electrode was examined as a selective, simple and precise new electrochemical sensor for the determination of sulfite in water and wastewater samples.     

Stannum film electrode for square wave voltammetric determination of trace copper(II)

An anodic stripping voltammetric procedure for the determination of Cu(II) at an in situ-plated stannum film electrode (SnFE) was described. The results indicated that the SnFE had an attractive electroanalytical performance, with two distinct voltammetric stripping signals for copper and stannum, and showed the superior advantage for the determination of copper compared with the bismuth film electrode. Several experimental parameters were optimized. The SnFE exhibited highly linear behavior in the concentration range from 1.0 to 100.0 μg L⁻¹ of Cu(II) (r = 0.994) with the detection limit of 0.61 μg L⁻¹ (S/N = 3), and the relative standard deviation for a solution containing 40.0 μg L⁻¹ Cu(II) was 2.2% (n = 8). The procedure has been successfully applied for the determination of Cu(II) in lake water sample.     

Square-wave cathodic adsorptive stripping voltammetric determination of trace amounts of 2-mercaptobenzimidazole in water samples

A sensitive, simple and reproducible square-wave cathodic adsorptive stripping voltammetric method is developed for the determination of 2-mercaptobenzimidazole (MBIM) in different water samples using a static mercury drop electrode (SMDE) as a working electrode. The solution conditions and instrumental parameters were optimized for the determination of MBIM by square-wave cathodic adsorptive stripping voltammetry. This method is based on a sensitive adsorptive reduction peak of the MBIM at ?0.532 V vs. Ag/AgCl reference electrode in a Britton-Robinson buffer at pH 10.0. The linear concentration range was 20–600 ng ml^?1 when using 0.0 V as the accumulation potential. The detection limit of the method was calculated to be 8.41 ng ml^?1. The precision was excellent with relative standard deviations (n = 20) of 2.30%, 1.71%, 2.25% and 1.33% at MBIM concentrations of 40, 90, 200 and 500 ng ml^?1, respectively. The proposed voltammetric method is used for the determination of MBIM in different spiked water samples.     

Rapid voltammetric determination of maltol in some foods and beverages using a poly(methylene blue)/graphene-modified glassy carbon electrode

A novel poly(methylene blue)/graphene composite glassy carbon electrode was fabricated and the electrochemical behavior of maltol at the modified electrode was studied by cyclic voltammetry. In phosphate-buffered solution, the modified electrode exhibited excellent electrocatalytic activity towards the electrochemical oxidation of maltol. Under optimized conditions, the oxidation peak current showed a linear relationship with the concentrations of maltol in the ranges of 8.00?×?10^?7 to 4.00?×?10^?5 and 4.00?×?10^?5 to 5.40?×?10^?4 mol L^?1, with a detection limit of 6.50?×?10^?8 mol L^?1. The performance of the developed method was validated in terms of linearity (r?=?0.9981 and 0.9955), recovery (97.0?99.3 %), reproducibility (relative standard deviations?≤?3.1 %, n?=?6), and robustness. The method shows excellent sensitivity, selectivity, and reproducibility and has been successfully applied to analyzing maltol in a wide variety of food products.     

Preconcentration and voltammetric determination of trace myoglobin at a 6-mercaptopurine modified silver electrode

6-Mercaptopurine(6-MP) is covalently modified onto a silver electrode to construct a chemically modified electrode (CME). It exhibits the capability of selectively complexing myoglobin and can be applied as a selective biosensor for this compound. Myoglobin is accumulated onto the CME at 0.32 V (vs. SCE); after exchanging the medium it is determined by differential pulse stripping voltammetry. A cathodic stripping peak is obtained at 0.15 V (vs. SCE) by scanning the potential from 0.35 to –0.1 V. The peak currents are linearly proportional to the concentration of myoglobin in the range of 0.2 ～ 4 μg/mL with a relative standard deviation of 7.8%. The detection limit is about 0.1 μg/mL. The mechanism of the complexation is also discussed.     

Preconcentration and voltammetric determination of trace myoglobin at a 6-mercaptopurine modified silver electrode

6-Mercaptopurine(6-MP) is covalently modified onto a silver electrode to construct a chemically modified electrode (CME). It exhibits the capability of selectively complexing myoglobin and can be applied as a selective biosensor for this compound. Myoglobin is accumulated onto the CME at 0.32 V (vs. SCE); after exchanging the medium it is determined by differential pulse stripping voltammetry. A cathodic stripping peak is obtained at 0.15 V (vs. SCE) by scanning the potential from 0.35 to –0.1 V. The peak currents are linearly proportional to the concentration of myoglobin in the range of 0.2 ∼ 4 μg/mL with a relative standard deviation of 7.8%. The detection limit is about 0.1 μg/mL. The mechanism of the complexation is also discussed. Received: 30 January 1997 / Revised: 7 May 1996 / Accepted: 10 May 1996     

Differential pulse cathodic stripping adsorption voltammetric determination of trace amounts of lead using factorial design for optimization

A sensitive cathodic stripping voltammetric method is developed for determination of lead(II), with adsorptive collection of complexes with Pyrogallol red (PGR) on to a hanging mercury drop electrode. After accumulation of the complex at −0.80 V vs. Ag/AgCl reference electrode, the potential is scanned in a negative direction from −0.20 to −0.50 V with differential pulse method. Then the reduction peak current for the lead(II)-PGR complex is measured at −0.39 V. The influence of reagent and instrumental variables was completely studied by factorial design analysis. The optimum analytical conditions for the determination of lead(II) were established. Under optimum conditions, lead(II) determined in the range of 0.1-30.0 ng ml⁻¹ with a limit of detection of 0.06 ng ml⁻¹. The method is successfully applied to determination of lead(II) in water sample.     

Copper solid amalgam electrode as a simple and sensitive tool for voltammetric determination of the antineoplastic drug 5-fluorouracil in pharmaceuticals

Voltammetric behavior of the antineoplastic drug 5-fluorouracil is for the first time studied on polished copper solid amalgam electrode. It was proved that the presence of the copper in the electrode material is advantageous for the determination of 5-fluorouracil, and one well-developed cathodic signal belonging to the reduction of the absorbed complex of 5-fluorouracil–Cu(II) was found as suitable for its precise determination. The highest response was recorded in Britton–Robinson buffer of pH 8 and excellent results like repeatability of measurements and determination as well or limit of detection (1.2 × 10^?9 mol L^?1) were reached. Moreover, the proposed method was successfully applied to the analysis of pharmaceutical sample with excellent recovery (97.0–100.9%).     

Sensitive voltammetric sensor of dihydromyricetin based on Nafion/SWNT-modified glassy carbon electrode

A novel voltammetric sensor, based on single-walled carbon nanotubes (SWNT) dispersed in Nafion and modified glassy carbon electrode (GCE), was fabricated and used to determine the trace amounts of dihydromyricetin (DMY). The electrochemical behavior of DMY at this sensor was investigated in 0.1 mol L⁻¹ sulfuric acid solutions + 0.1 mol L⁻¹ NaCl by cyclic voltammetry and squarewave voltammetry. Compared with bare GCE, the electrode presented an excellent response of DMY through an adsorption-controlled quasi-reversible process. Under the optimum conditions, the response peak currents were linear relationship with the DMY concentrations in the range of 1.0 × 10⁻⁷–1.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 9 × 10⁻⁸ mol L⁻¹. Based on this voltammetric sensor, a simple and sensitive electroanalytical method for DMY was proposed and applied to quantitative determination of DMY in Ampelopsis grossedentata samples. In addition, the oxidation mechanism was proposed and discussed, which could be a reference for the pharmacological action of DMY in clinical study.     

Stripping voltammetric determination of trace amounts of mercury using a carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone

A carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone was used for the voltammetric determination of mercury(II). Mercury was preconcentrated onto the surface of the modified electrode only by the complexing effect of the modifier without application of potential (i.e. in open-circuit conditions). After exchange of the medium, the accumulated amount of mercury(II) was determined by differential pulse anodic stripping voltammetry. The response depended on the concentration of mercury in the bulk solution, preconcentration time, and other parameters. The detection limit was 0.1 g 1^–1 Hg(II) for a preconcentration time of 15 min. Preconcentration for suitable times yielded a linear calibration graph from 0.5 to 6000 g 1^–1 Hg(II). For multiple determinations (5 runs), the relative standard deviation was 5% for a concentration of 100 g 1^–1 Hg(II). The proposed procedure was used to determine trace mercury in plant and sewage sludge samples with good results.On leave from Hainan University, Hainan Peoples Republic of China     

An improved voltammetric method for the determination of trace amounts of uric acid with electrochemically pretreated carbon paste electrodes

Carbon paste electrodes, preanodized in alkaline medium at 1.4 V vs SCE for a short period of time, exhibit a great shift of the oxidation potential of uric acid in cathodic direction and a marked enhancement of its current response, compared to unpretreated electrodes. These effects are dependent on the preanodization potential and the time imposed on the electrodes as well as on the alkalinity of the supporting electrolyte. The enhanced voltammetric response can be used to determine uric acid in the concentration range of 5.0-4.0 x 10(4) mug/1 (3.0 x 10(-8)-2.4 x 10(-4)M) with a detection limit (3sigma) of 2.0 mug/1 (1.2 x 10(-8)M). Ascorbic acid in less than 30-fold excess does not interfere. For multiple determinations (5 runs), the relative standard deviation is 2.1% at a concentration of 1 mg/1 uric acid. The proposed procedure can be used to determine uric acid in human urine and serum without any preliminary treatment of the samples in an accurate, rapid and simple way.     

A novel poly(cyanocobalamin) modified glassy carbon electrode as electrochemical sensor for voltammetric determination of peroxynitrite

This report described the direct voltammetric detection of peroxynitrite (ONOO⁻) at a novel cyanocobalamin modified glassy carbon electrode prepared by electropolymeriation method. The electrochemical behaviors of peroxynitrite at the modified electrode were studied by cyclic voltammetry. The results showed that this new electrochemical sensor exhibited an excellent electrocatalytic activity to oxidation of peroxynitrite. The mechanism of catalysis was discussed. Based on electrocatalytic oxidation of peroxynitrite at the poly(cyanocobalamin) modified electrode, peroxynitrite was sensitively detected by differential pulse voltammetry. Under optimum conditions, the anodic peak current was linear to concentration of peroxynitrite in the range of 2.0 × 10⁻⁶ to 3.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁷ mol L⁻¹ (S/N of 3). The proposed method has been applied to determination of peroxynitrite in human serum with satisfactory results. This poly(cyanocobalamin) modified electrode showed high selectivity and sensitivity to peroxynitrite determination, which could be used in quantitative detection of peroxynitrite in vivo and in vitro.     

Use of the differential pulse cathodic adsorptive stripping voltammetric method for the simultaneous determination of trace amounts of cadmium and zinc

A selective and sensitive method for the determination of cadmium and zinc is presented. The method is based on the adsorptive accumulation of the complexes of Cd(II) and Zn(II) ions with 4-amiono-5-methyl-2.4-dihydro-3H-1,2,4-triazol-3-tion (MMTT) onto hanging mercury drop electrode (HMDE), followed by the reduction of the adsorbed species using a voltammetric scan using differential pulse modulation. The ligand concentration, pH, potential and time of accumulation, scan rate, and pulse height were optimized. Under the optimized conditions, a linear calibration curve was obtained for the concentration of Cd(II) and Zn(II) in the range of 5–450 and 5–850 ng/mL, respectively, with a detection limit of 1.7 ng/mL Cd(II) and 1.3 ng/mL Zn(II). The ability of the method was evaluated by analysis of cadmium and zinc in water and alloy samples The text was submitted by the authors in English.     

Ultra trace adsorptive stripping voltammetric determination of atrazine in soil and water using mercury film electrode

In situ mercury film electrode produced in the presence of thiocyanate has been shown extremely useful for highly sensitive adsorptive stripping voltammetric measurements of atrazine down to sub-μg L⁻¹ level. Operational parameters have been optimized and the stripping voltammetric performance has been investigated using square wave scans. The adsorptive stripping response is linear over the range of 0.5-60 μg L⁻¹ atrazine, with a detection limit of 0.024 μg L⁻¹. The method has been applied to the determination of atrazine in soil and water samples.     

New methods for the determination of elements in trace amounts

Summary Recent methods for the determination of elements on trace amounts are discussed, which have been mainly developed in the author's laboratories. The review comprises the following sections: reagents and reactions, charge transfer reactions, candoluminescence, molecular emission spectroscopy in flames, enzymatic methods, gas-liquid chromatography of metal chelates, mass spectrometry of metal chelates.

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Neue Methoden zur Bestimmung von Elementen in Spurenmengen

Zusammenfassung Verfahren werden besprochen, die in den letzten Jahren hauptsächlich in den Laboratorien des Autors entwickelt wurden. Der Überblick umfaßt folgende Kapitel: Reagentien und Reaktionen, Charge-Transfer Reaktionen, Candoluminescenz, Molekular-Emissions-spektroskopie in Flammen, enzymatische Methoden, Gas-Flüssigkeits-Chromatographie von Metallchelaten und Massenspektrometrie von Metallchelaten.

Lecture presented at Euroanalysis I Conference, 28. 8.–1. 9. 1972 in Heidelberg, Germany.