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.     

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.     

Study on the Catalytic Determination of Vanadium (V) Using the Rhodamine 6G-Periodate Redox Reaction and its Analytical Application

 A fluorescence quenching method for the determination of vanadium (V) based on the vanadium- catalyzed oxidation of rhodamine 6G (R6G) with periodate in the presence of ethylenediaminetetraacetic acid disodium salt (EDTA) in sulfuric acid medium is described. The fluorescence was measured with excitation and emission wavelengths of 525 and 555 nm, respectively. The calibration graph for vanadium (V) had linear ranges of 3.0 × 10⁻⁹–1.5 × 10⁻⁸ mol/l and 1.5 × 10⁻⁸–4.0 × 10⁻⁸ mol/l, respectively. The detection limit was 1.7 × 10⁻⁹ mol/l. The proposed method was successfully applied to the determination of vanadium (V) in river water, rain water and cast iron samples. Received June 29, 2001 Revision October 9, 2001     

Electrochemical behavior and voltammetric determination of metol using a multiwall carbon nanotubes modified electrode

Electrochemical behavior of metol, which coexists with p-benzeneiol (HQ) at a glassy-carbon electrode modified with multiwall carbon nanotubes (MWNT/GCE), is studied in the thesis. The results indicate that metol yields a well-defined peak of which two concomitant reductive peaks separate and the potential separation reaches to 178 mV, and that concomitant HQ has almost no interference with the reduction signal of metol. The values of the reductive peak current (I _pc) are found to be linearly related to metol concentration over the range of 8.0 × 10⁻² −1.0 × 10⁻⁵ M, with a detection limit of 5.0 × 10⁻⁶ M. Some common matter has no interference with the determination of metol. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 1, pp. 31–35. The text was submitted by the authors in English.     

Chemiluminescence determination of chromium(III) and total chromium in water samples using the periodate-lucigenin reaction

A new chemiluminescence (CL) method combined with flow injection technique is described for the determination of Cr(III) and total Cr. It is found that a strong CL signal is generated from the reaction of Cr(III), lucigenin and KIO₄ in alkaline condition. The determination of total Cr is performed by pre-reduction of Cr(VI) to Cr(III) by using H₂SO₃. The CL intensity is linearly related to the concentration of Cr in the range 4.0 × 10⁻¹⁰–1.0 × 10⁻⁶ g mL⁻¹. The detection limit (3s _b) is 1 × 10⁻¹⁰ g mL⁻¹ Cr and the relative standard deviation is 1.9% (5.0 × 10⁻⁸ g mL⁻¹ of Cr(III) solution, n = 11). The method was applied to the determination of Cr(III) and total Cr in water samples and compared satisfactorily with the official method.     

Voltammetric Behavior of Strychnine, and its Determination in Strychno Nux-Vomica Seeds Extract

The voltammetric behavior of strychnine has been studied with a pyrolytic graphite (PG) electrode. The redox process taking place at the PG electrode is discussed. The cyclic voltammetric response has also been evaluated with respect to various experimental conditions, such as scan rate, pH of the supporting electrolyte, strychnine concentrations and accumulation time. A highly sensitive voltammetric method for the determination of strychnine is consequently developed. The linear calibration is in the range of 1×10⁻⁶ M – 1.1×10⁻⁴ M, with the limit of detection (LOD) being 1×10⁻⁸ M. The precision is excellent with a relative standard deviation (RSD) of 2.3%. The proposed cyclic voltammetric methodology has been applied to the determination of strychnine in the extract of Strychno nux-vomica seeds using the standard addition method. Consistent results have been obtained from both the electrochemical approach described here and the previously reported HPLC method.     

Molecularly imprinted on-line solid-phase extraction combined with chemiluminescence for the determination of pazufloxacin mesilate

A novel molecularly imprinted polymer solid-phase extraction (MISPE) with flow-injection chemiluminescence (CL) was developed for the determination of pazufloxacin mesilate (PZFX). The molecularly imprinted polymer (MIP) was synthesized by using PZFX as the imprinting molecule. A glass tube packed the particles of the MIP was employed as MISPE micro-column, which was connected into the sampling loop of the eight-way injection valve for on-line selective preconcentration and extraction of PZFX. The eluent of acetonitrile:acetic acid (9:1, v:v) was used as carrier for eluting the adsorbed PZFX to react with the mixture of cerium(IV) and sodium sulfite in the flow cell to produce strong CL. The relative intensity of CL was linear to PZFX concentration in the range from 2.5 × 10⁻⁹ to 2.5 × 10⁻⁷ g mL⁻¹. The limit of detection was 7 × 10⁻¹⁰ g mL⁻¹ (3 σ) and the relative standard deviation for 5 × 10⁻⁸ g mL⁻¹of PZFX solution was 3.7% (n = 7). This method has been applied to the determination of PZFX in human urine.     

Flavonol Derivatives for Determination of Cr(III) and W(VI)

 Simple, rapid, sensitive and selective methods for the determination of Cr(III) and W(VI) with flavonol derivatives in the presence of surface-active agents are proposed. In the pH ranges 3.4–4.2 and 1.9–2.5, the molar absorptivities of Cr(III)-morin-emulsifier S (EFA) and W(VI)-morin-polyvinylpyrrolidone (PVP) systems are 1.13×10⁵ and 2.13×10⁴ L mol⁻¹ cm⁻¹ at 435 and 415 nm, respectively. The Cr(III)-quercetin-PVP and W(VI)-quercetin-cetylpyridinium bromide (CPB) systems are formed in the pH ranges 4–4.6 and 2.2–2.8 with molar absorptivities 1.02×10⁵ and 9.02×10⁴ L. mol⁻¹ cm⁻¹ at 441 and 419 nm, respectively. The linear dynamic ranges for the determination of Cr(III) and W(VI) with morin in the presence of EFA and PVP are 0.03–0.46 and 0.71–8.1 μg mL⁻¹, respectively. The corresponding ranges with quercetin are 0.04–0.54 and 0.14–2.1 μg mL⁻¹ of Cr(III) and W(VI), respectively. The r.s.d (n = 10) for the determination of 0.25 and 3.7 μg mL⁻¹ of Cr(III) and W(VI) with morin and their detection limits are 0.88 and 0.99% and 0.016 and 0.63 μg mL⁻¹, respectively. Using quercetin, the r.s.d (n = 10) for 0.22 and 1.2 μg mL⁻¹ of Cr(III) and W(VI) and their detection limits are 0.92 and 0.91% and 0.015 and 0.08 μg mL⁻¹, respectively. The critical evaluation of the proposed methods is performed by statistical analysis of the experimental data. The proposed methods are applied to determine Cr in steel, non-ferrous alloys, wastewater and mud filtrate and to the determination of W in steel. Received March 8, 1999. Revision January 21, 2000.     

An electrochemiluminescence sensor for determination of durabolin based on CdTe QD films by layer-by-layer self-assembly

This work reported for the first time the use of flow injection electrochemiluminescence (FI-ECL) sensor for the determination of durabolin in an aqueous system based on CdTe quantum dot (QD) films. Aqueous CdTe colloidal solutions were prepared using thioglycolic acid as a capping agent. Zetasizer Nano ZS (Malvern, UK) was employed to characterize the size of CdTe QDs. The UV–vis and photoluminescence spectra of samples were systematically characterized. Indium tin oxide (ITO) slide glass was modified with CdTe QDs by layer-by-layer self-assembly. CdTe QD films were packed into a homemade cell and used as a recognizer of the FI-ECL sensor to determine durabolin. The intensive anodic ECL emission was obtained at a starting potential of +1.3 V (vs. Ag/AgCl) in a carbonate bicarbonate buffer solution with a pH of 9.93 at an ITO electrode. The ECL intensity was correlated linearly with the concentration of durabolin over the range of 1.0 × 10⁻⁸–1.0 × 10⁻⁵ g mL⁻¹, and the detection limit was 2.5 × 10⁻⁹ g mL⁻¹. The relative standard deviation for the determination of 1.0 × 10⁻⁶ g mL⁻¹ durabolin was 1.04% (n = 11). This simple and sensitive sensor revealed good reproducibility for ECL analysis. As a result, the new FI-ECL sensor had been successfully applied to the determination of durabolin in food samples. This strategy could be easily realized and opened new avenues for the applications of QDs in ECL biosensing.     

A New Differential Pulse Voltammetric Method for the Determination of Nitrate at a Copper Plated Glassy Carbon Electrode

 A differential pulse voltammetric method for the determination of nitrate has been described, which is applicable to the analysis of natural water samples with nitrate levels greater than 2.8 × 10⁻⁶ M. A reduction peak for the nitrate ions at a freshly copper plated glassy carbon electrode was observed at about −0.50 V vs Ag ∣AgCl∣KCl_satd electrode in a solution of 2.0 × 10⁻² M Cu²⁺, 0.5 M H₂SO₄ and 1.0 × 10⁻³ M KCl and exploited for analytical purposes. The working linear range was established by regression analysis and found to extend from 2.8 ×10⁻⁶ M to 8.0 × 10⁻⁵ M. The proposed method was applied for the determination of nitrate in natural waters. The detection limit of the method was 2.8 × 10⁻⁶ M and the sensitivity was 0.9683 A·L/mol. The possible interferences by some ions such as phosphate, nitrite and some halides were determined and found to lead to shifts of the peak position and increasing the peak heights. Received March 15, 1999. Revision July 9, 1999.     

Chemiluminescence determination of atenolol in biological fluids by a europium-sensitized permanganate-sulfite system

A simple flow injection chemiluminescence (CL) method was developed for the determination of atenolol using Eu³⁺ as the probe. It was found that the weak CL generated by the KMnO₄-Na₂SO₃ reaction can be significantly enhanced by the atenolol-Eu³⁺ complex. The experimental conditions were optimized. The CL intensity was linearly related to atenolol concentration in the range from 8.0 × 10⁻⁹ to 1.0 × 10⁻⁵ g mL⁻¹. The detection limit (3s _b) was 3 × 10⁻⁹ g mL⁻¹ and the relative standard deviation for 1.0 × 10⁻⁷ g mL⁻¹ atenolol solution was 2.4% (n = 11). The method has high sensitivity, wide linear range, inexpensive instrumentation, and has been applied to the determination of atenolol in spiked human urine and plasma samples with recoveries within the range 95.5–104.0%. Supplementary material to this paper is available in electronic form at Electronic supplementary material: Discussion of the reaction mechanism and additional figures are available online as electronic supplementary material (ESM) at . Correspondence: Jianxiu Du, Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, P.R. China     

Voltammetric study of the interaction of the ofloxacin–copper complex with DNA, and its analytical application

The electrochemical behavior of the ofloxacin–copper complex, Cu(II)L₂, at a mercury electrode, and the interaction of DNA with the complex have been investigated. The experiments indicate that the electrode reaction of Cu(II)L₂ is an irreversible surface electrochemical reaction and that the reactant is of adsorbed character. In the presence of DNA, the formation of the electrochemically non-active complexes Cu(II)L₂-DNA, results in the decrease of the peak current of Cu(II)L₂. Based on the electrochemical behavior of the Cu(II)L₂ with DNA, binding by electrostatic interaction is suggested and a new method for determining nucleic acid is proposed. Under the optimum conditions, the decrease of the peak current is in proportional to the concentration of nucleic acids in the range from 3 × 10⁻⁸ to 3 × 10⁻⁶ g · mL⁻¹ for calf thymus DNA, from 1.6 × 10⁻⁸ to 9.0 × 10⁻⁷ g · mL⁻¹ for fish sperm DNA, and from 3.3 × 10⁻⁸ to 5.5 × 10⁻⁷ g · mL⁻¹ for yeast RNA. The detection limits are 3.3 × 10⁻⁹, 6.7 × 10⁻⁹ and 8.0 × 10⁻⁹ g · mL⁻¹, respectively. The method exhibits good recovery and high sensitivity in synthetic samples and in real samples.     

Preconcentration and Voltammetric Study of Nicergoline at a Carbon Paste Electrode

 The electrochemical oxidation of nicergoline is investigated using cyclic and differential pulse voltammetry at a carbon paste electrode. For the determination of nicergoline an adsorptive stripping procedure is proposed. The response is characterized with respect to pH, ionic strength, preconcentration time, accumulation potential, nicergoline concentration, reproducibility and other variables. By differential pulse voltammetry at a carbon paste electrode and pH 8.0, a linear calibration in the range 5×10⁻⁸ M to 1×10⁻⁷ M and a detection limit of 1×10⁻⁸ M are obtained. The preconcentration medium-exchange approach was used for a selective determination of nicergoline in urine. For dilute urine samples a detection limit of 5×10⁻⁸ M is obtained after 3 min of accumulation and medium-exchange. The procedure also is applied for the determination of nicergoline in dosage form. Received August 24, 1998. Revision April 8, 1999.     

Voltammetric and Spectrophotometric Determination of Nizatidi ne in Pharmaceutical Formulations

 Two methods are described for quantitative determination of nizatidine. The first is a cathodic stripping voltammetric method which is based on the accumulation of the compound at the hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect of accumulation time, potential, concentration, pH and other variables. A linear calibration graph was obtained over the range 3.0×10⁻⁸–1.0×10⁻⁶ M with a detection limit 3.0×10⁻⁸ M after a 20s accumulation time at −0.2 V accumulation potential. On the other hand, it was found that the detection limit could be lowered to 1.0×10⁻⁸ M after 180s accumulation time at −0.2 V accumulation potential. The relative standard deviation was in the range 1.2−2.0% for six measurements. The tolerance amounts of the common excipients have also been reported. The second is a spectrophotometric method which is based on the formation and extraction of the ion-pair complex formed between nizatidine and either bromocresol green or bromothymol blue. The extracted colored ion-pair complexes absorb at 416 nm. The effect of different factors such as: type of organic solvent, pH, reagent concentration, number of extraction times, shaking time, temperature and the tolerance amount of the common excipients have been reported. The calibration graph was linear in the range 6.0×10⁻⁷–1.8×10⁻⁵ M with a detection limit of 6.0×10⁻⁷ M and molar absorptivity of 2.1×10⁴ lċmol⁻¹ċcm⁻¹ when using bromocresol green, while the calibration graph was linear in the range 3.0×10⁻⁷–1.1×10⁻⁵ M with a detection limit of 3.0×10⁻⁷ M and molar absorptivity of 3.2×10⁴ lċmol⁻¹ċcm⁻¹ when using bromothymol blue. The spectrophotometric methods offer alternative methods with reasonable sensitivity, selectivity and accuracy with relative standard deviation in the range 2.1−6.0% and 1.2−4.7% (for six measurements) when using bromothymol blue and bromocresol green, respectively. The proposed two methods were applied for the determination of nizatidine in commercially available dosage forms. A comparison between the voltammetric and the extraction-spectrophotometric methods was also reported. Received April 19, 1999. Revision August 30, 1999.     

Determination of trace vanadium in soil by cloud point extraction and graphite furnace atomic absorption spectroscopy

This work describes a new analytical procedure for trace vanadium by graphite furnace atomic absorption spectroscopy coupled to cloud point extraction (CPE) as the separation-preconcentration method. The CPE behavior of vanadium using methylene blue as complex agent and Triton X-100 as a surfactant was investigated systematically. Under the optimized conditions, the detection limit was 0.7 ng · mL⁻¹, and the relative standard deviation was 4.3% for vanadium (c = 50.0 ng · mL⁻¹, n = 5). The recovery of vanadium was in the range of 98.9–102.8%. The method was applied to the analysis of vanadium in certified reference materials and real samples. The results obtained were in good agreement with the certified values. Correspondence: Xiashi Zhu, Key Laboratory of Environmental Material and Environmental Engineering of Jiangsu province/College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, P.R. China     

Construction and Evaluation of a Promazinium Cation-Selective Electrode

 The construction of a plasticised PVC matrix-type promazinium cation-selective membrane electrode and its use in the potentiometric determination of promazine hydrochloride in pharmaceutical preparations are described. It is based on the use of the ion-associate species, formed by promazinium cation and tetraphenylborate (TPB) counter ion. The basic electrode performance characteristics are evaluated according to IUPAC recommendations. It exhibited a linear response for 1 × 10⁻²−1 × 10⁻⁵ M of promazine hydrochloride solutions with a cationic Nernstian slope over the pH range 2–6. Common organic and inorganic cations showed negligible interference. Direct potentiometric determination of 1 × 10⁻²−1 × 10⁻⁵ M aqueous promazine hydrochloride using this membrane electrode system showed an average recovery of 99.5% with a mean standard deviation of 1.5%. This electrode was successfully used for monitoring the titration of promazine hydrochloride with sodium tetraphenyl borate and for determining promazine hydrochloride in ampoules. Received June 15, 2001 Revision November 6, 2001     

Quantitation of bacteria through adsorption of intracellular biomolecules on carbon paste and screen-printed carbon electrodes and voltammetry of redox-active probes

A new electrochemical method for the quantitation of bacteria that is rapid, inexpensive, and amenable to miniaturization is reported. Cyclic voltammetry was used to quantitate M. luteus, C. sporogenes, and E. coli JM105 in exponential and stationary phases, following exposure of screen-printed carbon working electrodes (SPCEs) to lysed culture samples. Ferricyanide was used as a probe. The detection limits (3s) were calculated and the dynamic ranges for E. coli (exponential and stationary phases), M. luteus (exponential and stationary phases), and C. sporogenes (exponential phase) lysed by lysozyme were 3 × 10⁴ to 5 × 10⁶ colony-forming units (CFU) mL⁻¹, 5 × 10⁶ to 2 × 10⁸ CFU mL⁻¹ and 3 × 10³ to 3 × 10⁵ CFU mL⁻¹, respectively. Good overlap was obtained between the calibration curves when the electrochemical signal was plotted against the dry bacterial weight, or between the protein concentration in the bacterial lysate. In contrast, unlysed bacteria did not change the electrochemical signal of ferricyanide. The results indicate that the reduction of the electrochemical signal in the presence of the lysate is mainly due to the fouling of the electrode by proteins. Similar results were obtained with carbon-paste electrodes although detection limits were better with SPCEs. The method described herein was applied to quantitation of bacteria in a cooling tower water sample. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Derivative Spectrophotometric Determination of Nd, Ho and Er in Rare Earth Mixtures with 1-Ethyl-6,8-difluoro-7-(3-methyl-1-piperazinyl)-4-oxo-1,4-dihydro-3-quinoline carboxylic acid

 The second derivative spectrophotometric method has been developed as a procedure for the determination of neodymium, holmium and erbium in mixed rare earths. It was found that the 1-ethyl-6, 8-difluoro-7-(3-methyl-1-piperazinyl)-4-oxo-1,4- dihydro-3-quinoline carboxylic acid forms stable complexes with neodymium, holmium and erbium ions in the pH 9.2–10.5 range. In the second derivative spectra the optimum analytical signals for neodymium, holmium and erbium are at 576.2 (+)−574.5 (−)nm, 444.2 (+) −447.8 (−)nm and 516.0 (+) −517.2(−)nm, respectively. Beer’s law is obeyed from 5.0×10⁻⁵ M to 2.5×10⁻⁴ M of neodymium, holmium and erbium. The quantification limits (10 Sb) were 1.2×10⁻⁵ M for Nd, 9.7×10⁻⁵ M for Ho and 3.0×10⁻⁶ M for Er. Received April 22, 1998. Revision March 8, 1999.     

Development of membrane electrodes for selective determination of some antiepileptic drugs in pharmaceuticals,plasma and urine

Newly developed, simple, low-cost and sensitive ion-selective electrodes have been proposed for determination of some antiepileptic drugs such as lamotrigine, felbamate, and primidone in their pharmaceutical preparations as well as in biological fluids. The electrodes are based on poly(vinyl chloride) membranes doped with drug–tetraphenyl borate (TPB) or drug–phosphotungstic acid (PT) ion-pair complexes as molecular recognition materials. The novel electrodes displayed rapid Nernstian responses with detection limits of approximately 10⁻⁷ M. Calibration graphs were linear over the ranges 5.2 × 10⁻⁷–1.0 × 10⁻³, 1.5 × 10⁻⁶–1.0 × 10⁻³, and 2.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–TPB and 5.8 × 10⁻⁷–1.0 × 10⁻³, 1.8 × 10⁻⁷–1.0 × 10⁻³, and 6.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–PT electrodes, respectively, with slopes ranging from 52.3 to 62.3 mV/decade. The membranes developed have potential stability for up to 1 month and proved to be highly selective for the drugs investigated over other ions and excipients. The results show that the selectivity of the ion-selective electrodes is influenced significantly by the plasticizer. The proposed electrodes were successfully applied in the determination of these drugs in pharmaceutical preparations in four batches of different expiry dates. Statistical Student’s t test and F test showed insignificant systematic error between the ion-selective electrode methods developed and a standard method. Comparison of the results obtained using the proposed electrodes with those found using a reference method showed that the ion-selective electrode technique is sensitive, reliable, and can be used with very good accuracy and high percentage recovery without pretreatment procedures of the samples to minimize interfering matrix effects. Figure Structure of lamotrigine, felbanate and primidone     

Application of a trazodone-selective electrode to pharmaceutical quality control and urine analyses

A trazodone-selective electrode for application in pharmaceutical quality control and urine analysis was developed. The electrode is based on incorporation of a trazodone-tetraphenylborate ion exchanger in a poly(vinyl chloride) membrane. The electrode showed a fast, stable and Nernstian response over a wide trazodone concentration range (5 × 10⁻⁵−1 × 10⁻² M) with a mean slope of 59.3 ± 0.9 mV/dec of concentration, a mean detection limit of 1.8 × 10⁻⁵± 2.2 × 10⁻⁶ M, a wide working pH range (5–7.5) and a fast response time (less than 20 s). The electrode also showed good accuracy, repeatability, reproducibility and selectivity with respect to some inorganic and organic compounds, including the main trazodone metabolite. The electrode provided good analytical results in the determination of trazodone in pharmaceuticals and spiked urine samples; no extraction steps were necessary. Dissolution testing of trazodone tablets, in different conditions of pH and particle size, based on a direct potentiometric determination with the new selective electrode is presented as well.