A simple optical sensor for cadmium ions assay in water samples using spectrophotometry

A new simple and inexpensive optical chemical sensor for cadmium(II) ions is presented. The cadmium sensing system was prepared by incorporating 2-amino-cyclopentene-1-dithiocarboxylic acid (ACDA) on a triacetylcellulose membrane. The absorption spectra of the optical sensor membrane in Cd(II) solution showed a maximum peak at 430 nm. The proportionality in intensity of the membrane color on the optode to varying amounts of Cd(II) suggests its potential applications for screening Cd(II) in aqueous samples by visual colorimetry. The sensor provided a wide concentration range of 3.0 × 10⁻⁶–3.4 × 10⁻⁴ M of Cd(II) ions with a detection limit of 1.0 × 10⁻⁶ M (0.2 μg/mL). The relative standard deviations for eight replicate measurements of 8.0 × 10⁻⁶ and 5.0 × 10⁻⁵ M Cd(II) were 2.7 and 2.3%, respectively. The response time of the optode was 6 min. The influence of interfering ions on the determination of 1.0 × 10⁻⁵ M Cd(II) was studied and the main interferences were removed by extraction method. The sensor was applied to the determination of Cd(II) in water samples.     

Capillary electrophoretic speciation of Cu(II) and Co(III) in the electroless copper plating baths

Summary A capillary electrophoretic method for the determination of Cu(II) and Co(III) chelates with ethylenediamine in electroless copper plating baths has been developed. The influence of carrier electrolyte parameters such as nature of counter-ion and pH were studied and discussed. The optimised separations were carried out in a fused silica capillary (57 cm × 75 μm I.D.) filled with an ethylenediamine sulfate electrolyte (20 mol L⁻¹ ethylendiamine, pH7.0 with H₂SO₄; applied voltage, +25 kV) using direct UV detection at 214 nm. The detection limits for a signalto-noise ratio of 3 and 10s hydrodynamic injection were 5×10⁻⁶ mol L⁻¹ for Cu(II) and 1×10⁻⁶ mol L⁻¹ for Co(III). The relative standard deviations of the peak areas for Cu(II) and Co(III) were found to be 1.5% and 2.4%, respectively, with five consecutive injections of standard solution containing 5×10⁻⁵ mol L⁻¹ of each metal ion. Application of the method to the speciation of Cu(II) and Co(III) complexes in copper plating bath samples is also demonstrated.     

A kinetic method for the determination of organosulfur compounds by inhibition: determination of cysteine, 2,3-dimercaptopropanol and thioglycolic acid

A kinetic method for the determination of organosulfur compounds by UV spectrophotometry is described. Organosulfur compounds have been shown to inhibit the Hg(II)-catalyzed substitution of cyanide in hexacyanoferrate(II) by 2-methylpyrazine (2-Mepz). The inhibitory effect is proportional to the concentration of inhibitor and can be used as the basis for the determination of trace amounts of organosulfur compounds such as cysteine, 2,3-dimercaptopropanol (DMP) and thioglycolic acid (TGA). Both the influence of the reaction variables and interference of a variety of ions have been studied. A mechanism for the inhibition process is proposed. The determination range depends on the amount of Hg(II) added and stability of the Hg(II)–ligand complex. Kinetic parameters were determined from Lineweaver–Burk plots, obtained in the absence and presence of the inhibitor. Excellent linearity is observed for all analytes over their respective concentration ranges with correlation coefficient >0.9. The condition calibration curves were linear in the range of 5 × 10⁻⁶–15 × 10⁻⁶ M for cysteine, 1 × 10⁻⁷–7 × 10⁻⁷ M for DMP and 1 × 10⁻⁶–10 × 10⁻⁶ M for TGA. The detection limits were 1.18 × 10⁻⁷ M for cysteine, 4.16 × 10⁻⁸ M for DMP and 1.30 × 10⁻⁷ M for TGA. The effects of amino acids that can interfere in the determination of cysteine were studied.     

Photometric determination of aqueous cobalt (II), nickel (II), copper (II) and iron (III) with 1-nitroso-2-naphthol-3,6-disulfonic acid disodium salt in gelatin films

Photometric determination of aqueous Co(II), Cu(II), Ni(II) and Fe(III) was performed using indicator films prepared by immobilization of 1-nitroso-2-naphthol-3,6-disulfonic acid disodium salt (NRS) into hardened photographic film. Immobilization was based on electrostatic interaction of reagent and metal complexes with the gelatin. The isoelectric point pH of hardened gelatin (4.46±0.04) was evaluated by viscometry. Co(II), Fe(III), Ni(II) form 1:3 complexes with NRS in gelatin at pH 2 and Cu(II) forms 1:2 complexes. Their log β′ values were: Co-6.7, Fe-8.6, Cu-8.0, and Ni-6.4. The absorption maxima were: 370nm for NRS, and 430nm, 470nm, 495nm and 720nm for complexes of Co(II), Ni(II), Cu(II) and Fe(III). An algorithm for their simultaneous determination using the indicator films was developed. The detection limits were: c_lim(Co²⁺) = 0.45×10⁻⁵ M, c_lim(Fe³⁺) = 0.50×10⁻⁵ M, c_lim(Cu²⁺) = 0.67×10⁻⁵ M, c_lim(Ni²⁺) = 0.75×10⁻⁵ M,; and their sum c_lim(ΣMn⁺) = 0.82×10⁻⁵ M.      

Electrochemical Reduction of Benzaldehyde as its Girard-P Derivative at the Mercury Electrode and Differential-Pulse Polarographic Determination of Benzaldehyde

 The polarographic behaviour of benzaldehyde as its Girard-P derivative was studied using various electrochemical techniques and a method for the determination of benzaldehyde (10⁻⁶ − 8 × 10⁻⁵ M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.7% (ten determinations at the 5 × 10⁻⁵ M level). The applicability of this method is checked in benzyl alcohol and synthetic samples containing, o-aminophenol, 2-amino pyridine, o-cresol, amylic alcohol, salicylic acid, 4-aminobenzoic acid and naphthalene sulfonic acid. Received April 6, 2000. Revision February 13, 2001.     

Construction of different types of ion-selective electrodes and validation of direct potentiometric determination of phenytoin sodium

The construction and performance characteristics of phenytoin sodium selective electrodes are detailed. Two types of electrodes: plastic membrane I and coated wire II, were constructed based on the incorporation of phenytoin sodium with tungstosilicic acid. The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time and the electrodes’ foreign ions were investigated. The electrodes showed a Nernstian response with a mean calibration graph slope of 30.9±0.1 and 28.9±0.1 mV decade⁻¹ at 25°C for electrode I and II respectively, over a phenytoin sodium concentration range of 5×10⁻³−5×10⁻⁶ M and 1×10⁻³−1×10⁻⁶ M with a detection limit 1.3×10⁻⁶ M and 2.5×10⁻⁷ M for electrode I and II, respectively. The electrodes gave average selective precision and were usable within the pH range 6–10. Interference studies from common cations, alkaloids, sugars, amino acids and drug excipients are reported. The results obtained by the proposed electrodes were also applied successfully for the determination of the drug in pharmaceutical preparations and biological fluids.     

Subnanomolar determination of a beryllium ion by a novel Be(II) microsensor based on 4-nitrobenzo-9-crown-3-ether

In this work, for the first time, we introduce a highly selective and sensitive Be(II) microsensor. 4-nitrobenzo-9-crown-3-ether (NBCE) was used as a membrane-active component to prepare a Be(II)-selective polymeric membrane microelectrode. The electrode exhibits a Nernstian response toward Be(II) ions over a very wide concentration range (1.0 × 10⁻⁴–1.0 × 10⁻¹⁰ M), with a detection limit of 3.5 × 10⁻¹¹ M (∼350 pg/L). In fact, the electrode presents a fast response time in the whole concentration range (6 s). The proposed microelectrode can be used for at least six weeks without any considerable divergence in the potentials. The proposed membrane sensor revealed a selectivity toward Be(II) ions over a wide variety of other metal ions including common alkali, alkaline-earth, and rare-earth ions. It could be used in the pH range of 3.0–11.5. The microelectrode was successfully used as an indicator electrode for the titration of 20 mL of 1.0 × 10⁻⁶ M Be²⁺ solution with 1.0 × 10⁻⁴ M of EDTA. It was also applied to the direct determination of beryllium ions in beryl and binary mixtures. The text was submitted by the authors in English.     

Reagentless biosensor for phenolic compounds based on tyrosinase entrapped within gelatine film

A simple and new reagentless phenolic compound biosensor was constructed with tyrosinase immobilized in the gelatine matrix cross-linked with formaldehyde. The morphologies of gelatine and gelatine/tryosinase were characterized by SEM. The tyrosinase retains its bioactivity when being immobilized by the gelatine film. Phenolic compounds were determined by the direct reduction of biocatalytically liberated quinone at -0.1 V vs SCE. The process parameters for the fabrication of the enzyme electrode were studied. Optimization of the experimental parameters has been performed with regard to pH, operating potential, temperature and storage stability. This biosensor exhibits a fast amperometric response to phenolic compounds. The linear range for catechol, phenol, and p-Cresol determination was from 5×10⁻⁸ to 1.4×10⁻⁴ M, 5×10⁻⁸ to 7.1×10⁻⁵ M, and 1×10⁻⁷ to 3.6×10⁻⁵ M, with a detection limit of 2.1×10⁻⁸ M, 1.5×10⁻⁸ M, and 7.1×10⁻⁸ M, respectively. The enzyme electrode retained ca.77% of its activity after 7 days of storage at 4°C in a dry state. The proposed sensor presented good repeatability, evaluated in terms of relative standard deviation (R.S.D.=8.6%) for eight different biosensors and was applied for determination in water sample. The recovery for the sample was from 99.0% to 99.8%.     

Simultaneous electrochemical detection of uric acid and ascorbic acid at a silver doped poly(glutamic acid) modified glassy carbon electrode

In this paper, the silver doped poly (L-glutamic acid) modified glassy carbon electrode (PLG-Ag/GCE) was fabricated through an electrochemical immobilization. The modified electrode was used for simultaneous determination of uric acid (UA) and ascorbic acid (AA) in 0.1 M phosphate buffer solutions (PBS). The cyclic voltammetric signals of UA and AA were well separated with a potential difference of 396 mV in pH 3.0 phosphate buffer solution. The linear calibration curves were obtained in the concentration range 5.00 × 10⁻⁷–1.00 × 10⁻⁴ M for UA and 8.00 × 10^-6–5.00 × 10⁻³ M for AA with the detection limits of 3 × 10⁻⁷ M and 4 × 10⁻⁶ M, respectively. The relative standard deviations were 1.3 and 1.0% for the determinations of UA and AA for 20 continuous measurements. The signal was highly stable and reproducible. This method was successfully applied to the determination of UA in human urine samples.     

A lanthanide sensitized chemiluminescence method of flow-injection for the determination of ulifloxacin and prulifloxacin

A lanthanide sensitized chemiluminescence method of flow-injection was developed for the determination of a new fluoroquinolone, ulifloxacin (UFX), and its prodrug prulifloxacin (PUFX). The proposed method was based on the remarkable chemiluminescence enhancement effect of UFX (PUFX) on KMnO₄−Na₂S₂O₄−Ln(III). Tb(III) ion was chosen from lanthanides because it showed the best sensitizing effect. Under optimized experimental conditions, the relative chemiluminescence intensity was in linear relationship with UFX and PUFX concentrations in the ranges of 1.0 × 10⁻⁸ − 5.0 × 10⁻⁶ M and 9.0 × 10⁻⁹ − 5.0 × 10⁻⁶ M, respectively. The minimum detectable value and relative standard deviation were 5.5 × 10⁻⁹ M, 1.5% for UFX and 7.0 × 10⁻⁹ M, 2.9% for PUFX, respectively. The proposed method was applied to the determination of UFX in spiked human serum and urine, and of PUFX in tablets with satisfactory results. The possible mechanism of chemiluminescence was also proposed. The text was submitted by the authors in English.     

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.     

Spectrophotometric method for the determination of telmisartan with congo red

In pH 2.50 HCl-NaAc buffer solution, the reaction between telmisartan and congo red could form ionassociation complex, which has the maximum absorbance at 593 nm in the spectrophotometric experiment. Under this wavelength, the Beer’s law was obeyed within the concentration range of 1.08 × 10⁻⁶−2.24 × 10⁻⁵ M. The linear regression equation was A = −0.1913 × 10⁵ c + 0.0286 (C: M). The regression coefficient r was 0.9986. The apparent molar coefficient ɛ₅₉₃ was 1.63 × 10⁴ L mol⁻¹ cm⁻¹ and the detection limit was 5.66 × 10⁻⁷ M. The established method having high sensitivity and good selectivity could be applied to the determination of telmisartan in pharmaceutical, urine and blood plasma samples with satisfactory results. The reaction mechanism was also discussed by using density functional theory methods. The result obtained was consilient with experimental data. The article is published in the original.)     

Simultaneous voltammetric determination of epinephrine and serotonin at a p-tetra-butyl calix [6] arene-L-Histidine chemically modified electrode

A new p-tetra-butyl calix [6] arene-L-Histidine chemically modified glassy carbon electrode (BCH/GCE) has been proposed for simultaneous investigation and determination of epinephrine (Ep) and serotonin (5-HT) by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In potassium dihydrogen phosphate-borax (PDPB) buffer solution (pH 5.8), the anodic peaks of Ep and 5-HT were observed at 0.27 and 0.45 V, respectively, with E up to 180 mV. The peak currents on the DP voltammogram are in a linear relationship with the concentrations of Ep in the range of 1.0 × 10⁻⁶−1.30 × 10⁻⁴ M in the presence of 1.0 × 10⁻⁴ M 5-HT. A linear relationship was similarly found for 5-HT in the range 1.0 × 10⁻⁶⁻ 1.40 × 10⁻⁴ M in the presence of 1.0 × 10⁻⁴ M Ep. It is found that Ep and 5-HT could be simultaneously determined with good sensitivity in the presence of 1.0 × 10⁻³ M ascorbic acid (AA). The developed method has been applied to the determination of Ep and 5-HT in synthetic samples with satisfactory results. The text was submitted by the authors in English.     

Growth and characterization of Mn- and Co-doped ZnO nanowires

A flow injection chemiluminescence method is proposed for the determination of cobalt, based on the strong catalytic effect of Cobalt(II) (1,10-phenanthroline)₃ complex on the lucigenin-periodate reaction in alkaline medium. Under the optimum experimental conditions, the chemiluminescence signal responded linearly to the concentration of cobalt(II) in the 1.0 × 10⁻⁹–3.0 × 10⁻⁷ g mL⁻¹ range with a detection limit of 4.4 × 10⁻¹⁰ g mL⁻¹ cobalt(II). The relative standard deviation for the determination of 5.0 × 10⁻⁸ g mL⁻¹ of cobalt was 2.3% in eleven replicated measurements. The method was successfully applied to the determination of cobalt(II) in pharmaceutical preparations.     

Polarographic Catalytic Wave of Prednisone in the Presence of Persulfate and its Application

 A polarographic catalytic wave of prednisone in the presence of K₂S₂O₈ was observed. The polarographic catalytic wave of prednisone as catalyst was attributed to such chemical reaction parallel to electrode reaction as oxidized the free radical from one electron reduction of the Δ^1,4-3 keto group of prednisone to regenerate the original keto group. The catalytic wave can be used for the determination of prednisone with the help of conventional polarographic equipment, such as linear-potential scan polarograph. In 0.12 mol l⁻¹ HAc-0.08 mol l⁻¹ NaAc-0.014 mol l⁻¹ K₂S₂O₈ (pH 4.6) supporting electrolyte, the second-order derivative peak current of the catalytic wave was rectilinear to prednisone concentration in the range of 3.2 × 10⁻⁷∼1.6 × 10⁻⁵ mol l⁻¹. The detection limit was 8.0 × 10⁻⁸ mol l⁻¹. Received August 6, 2001; accepted April 17, 2002; published online July 22, 2002     

Determination of trace amounts of nitrite by single-sweep polarography

A single-sweep polarographic determination of nitrite in 0.2 M sulphuric acid medium containing nickel(II) sulphate and ammonium thiocyanate is described. The ternary complex (NiSCNNO)⁺ which is formed in the solution is strongly adsorbed on the surface of the mercury electrode and an adsorptive polarographic wave at ?0.57 V (vs. SCE) is related to the concentration of nitrite in the range 2.0 × 10^?8-1.0 × 10^?6 M. The detection limit is 8 × 10^?9 M. The relative standard deviation is 1.5% and the regression coefficient is 0.998. Most common anions and cations do not interfere. The mechanism of the electrode process was studied by several electrochemical methods. The polarographic wave is attributed to the reduction of nitrogen monoxide in the adsorbed (NiSCNNO)⁺ complex to hydroxylamine. The procedure was applied to the determination of trace amounts of nitrite in sausage, water and nitrate.     

A facile and fast electrochemical method for the simultaneous determination of <Emphasis Type="Italic">o</Emphasis>-dihydroxybenzene and <Emphasis Type="Italic">p</Emphasis>-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. The text was submitted by the authors in English.     

Estimation of performance parameters of a frontal variant of optoacoustic determination with a model system

Using a model system, the applicability of the frontal configuration of optoacoustic spectroscopy in analytical practice is shown. An optoacoustic cell made using layered-prism geometry was designed and tested; it ensures operation with a layer thickness of 20–100 μm and sample volumes of 50–100 μl. Conditions are proposed for determining iron(II) in the form of tris(1,10-phenanthrolinate) with the detection limit of 3 × 10⁻⁷ M, which is less that the detection limit under similar induction conditions and for the same determination procedure using thermal-lens spectrometry (4 × 10⁻⁷ M). The determination has high reproducibility (relative standard deviation for 10⁻⁶ M is 0.005) and expressivity (1 min per sample detection).     

Electroanalysis and determination of acetaldehyde in fuel ethanol using the reaction with 2,4-dinitrophenylhydrazine

The voltammetric reduction of acetaldehyde was studied in 0.1 M LiOH: LiCl (60: 40 v/v). Well-defined waves can be seen at −1.77 and −1.60 V with the use of hanging mercury and glassy carbon electrodes. Acetaldehyde was shown to react at room temperature with the 2,4-dinitrophenylhydrazine and the product exhibited a differential pulse voltammetric peak at −0.90 V, which was well separated from the peaks of the derivative. This allowed the indirect determination of acetaldehyde in the presence of 0.1 M ethanol/tetrabutylammonium perchlorate after 10 min of reaction. Calibration graphs were obtained for 1.00 × 10⁻⁶−1.00 × 10⁻⁴ M of acetaldehyde. The detection limit is 8.14 × 10⁻⁷ M. The method has been applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pretreatment. The text was submitted by the authors in English.     

Electrocatalytic determination of dopamine in pharmaceutical and human serum samples by using [N,N′-bis(2-pyridine carboxamido)-1,2-benzene] nickel(II) modified carbon paste electrode

The main purpose of this study is to develop an inexpensive, simple, selective and especially sensitive modified carbon paste electrode (MCPE) for the determination of dopamine (DA) in pharmaceutical and human serum samples. The carbon paste electrode (CPE) has been modified by using [N,N′-bis(2-pyridine carboxamido)-1,2-benzene] nickel(II) complex (Ni(II)bpb) and the electrochemical behavior of the modified electrode has been studied by cyclic voltammetry. The modified electrode shows an excellent electrocatalytic effect on the oxidation of DA. Under optimum conditions, calibration plots are found to be linear in the range of 7.0 × 10⁻⁷−1.0 × 10⁻⁵ M (r ₂ = 0.9940) and 1.0 × 10⁻⁵−1.0 × 10⁻⁴ M (r₂ = 0.9945); the detection limit is 6.2 × 10⁻⁸ M. The preparation of MCPE is very easy. The electrode can be renewed by simple polishing. The proposed method shows good sensitivity, reproducibility (RSD ∼ 2.9%), high stability (more than two month) without any considerable change in response and recovery for the determination of DA. The prepared electrode has been successfully applied to the voltammetric determination of DA in pharmaceutical and biological samples. The article is published in the original.