Indirect Differential Pulse Voltammetric Determination of Aluminum by a Pyrocatechol Violet-Modified Electrode

Aluminumhasbeenconsideredtobeacausativeagentforvariousneurologicaldisorders'.Duringthelastdecade,considerableattentionhasbeenpaidtotheelectrochemicaldeterminationofAlforitsdistinguishedmeritsofhighsensitivity,easymanipulationandsimpleinstrumentation...     

Differential Pulse Anodic Stripping Voltammetric Determination of Lead with Heparin Modified Electrode

Introduction Overall exposure to lead is of public health concern because of several hazardous effects that may occur to human beings. Lead poisoning may provoke irritability, anorexia, malaise and headache. Intoxication progress may lead to attacks of abdominal pain until coma and death.1 The determination of trace lead in variety of en-vironmental samples is of great importance since lead is recognized as a cumulative poison to animals and hu-mans. There is a constant demand for improved an…     

Utility of Certain σ and π-Acceptors for the Spectrophotometric Determination of Sildenafil Citrate (Viagra)

 The molecular interaction between sildenafil citrate as electron donor and each of iodine; 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); tetracyanoethylene (TCNE); 2,4,7-trinitro-9-fluorenon (TNF); chloranilic acid (CLA); chloranil (CL) and bromanil (BL) as acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studied and optimized. Beer’s law was obeyed in a concentration limit of 10–260 μg/mL for sildenafil citrate. For more accurate analysis, Ringbom optimum concentration range was found to be between 20–240 μg/mL. The limits of detection and determination were calculated and found to be 1.5 and 5.2 μg/mL, respectively. The standard deviations were calculated for different concentrations of sildenafil citrate using various acceptors. A Job’s plot of the absorbance versus the molar ratio of the sildenafil citrate to each of acceptors under consideration indicated (1:1) ratio. The proposed methods were found to be rapid, accurate, precise and sensitive and could be applied for determination of sildenafil citrate in pharmaceutical dosage forms (Viagra) without interferences from common additives encountered. Received August 30, 2000. Revision January 5, 2001.     

Anodic Stripping Voltammetric Determination of Mercury in Water Using a Chitosan‐Modified Carbon Paste Electrode

Abstract

This paper describes the preparation and electrochemical application of a modified carbon paste electrode with chitosan for the determination of Hg(II) ions in water using anodic stripping voltammetry. Experimental parameters, including the pH of the supporting electrolyte, time and potential of accumulation and scan rate were investigated. The best voltammetric response was observed for a paste composition of 60% (m/m) of graphite powder, 20% (m/m) of chitosan and 20% (m/m) of mineral oil, with 0.1 mol/l NaNO₃ solution at pH 6.3 as supporting electrolyte, a preconcentration potential of ?0.2 V, preconcentration time of 270 s and a scan rate of 25 mV/s. Under these optimal experimental conditions, the voltammetric signals were linearly dependent on the Hg(II) concentration in the range of 9.99×10^?7 to 3.85×10^?5 mol/l with a detection limit of 6.28×10^?7 mol/l. Three “spiked” samples of water were evaluated using the proposed sensor, and results agreed with those obtained by a reference method at the 95% confidence level.     

Determination of Tryptophan in Pharmaceutical Formulations Using a Sequential Injection–Zone Fluidic–Chemiluminescence Tubular Reactor

Tryptophan is an important amino acid for humans with a significant role in cell metabolism. Depletion of tryptophan in the human body may contribute to diseases and development of disorders among the human population. It is, therefore, very important to have a reliable, stable, sustainable, and cost-effective analytical method for the determination of tryptophan. Tryptophan was determined using sequential injection–zone fluidics analysis with luminol–hydrogen peroxide and the Firefly with its unique liquid core waveguide flow-cell design as chemiluminescence tubular reactor with a high-sensitivity photomultiplier tube. This was based on an intense chemiluminescence formation of tryptophan in luminol–hydrogen peroxide inside the tubular reactor for measurement. The chemiluminescence intensity was linear with tryptophan in the range of 1.0?×?10^?6 to 1.0?×?10^?3?mol/L, and the limit of detection was 7.5?×?10^?7?mol/L. The precision for the method was 3.6% (relative standard deviation) for six measurements of 1.0?×?10^?4?mol/L tryptophan. The proposed method has been used to determine tryptophan in pharmaceutical formulations. The system is relatively fast for online assays. Eighty seconds are required to complete one cycle providing a throughput of 45 samples/h. The proposed sequential injection analysis–zone fluidics–chemiluminescence system for the assay of tryptophan in certain specific pharmaceutical capsules is simple, reliable, sustainable, and convenient with relatively low-cost consumption of reagents.     

Direct and Simultaneous Determination of Phenol, Hydroquinone and Nitrophenol at Boron-Doped Diamond Film Electrode

The electrochemical characteristics of multi-component phenolic pollutants, such as phenol （Ph）, hydroquinone （HQ） and 4-nitrophenol （4-NP）, were investigated on boron-doped diamond （BDD） film electrode by differential pulse voltammetry （DPV） technique. A simple and feasible platform was accordingly established for the direct and simultaneous determination of these three phenolic pollutants. Results showed that, Ph, HQ and 4-NP gave obvious oxidation peaks on BDD electrode at the potential of 1.24, 0.76 and 1.52 V, respectively. Each of them displayed good linear relationship between their oxidation peak currents and their corresponding concentrations in a rather wide range coexisting with one or two of the other phenolic pollutants. The detection limits of Ph, HQ and 4-NP were estimated to be as low as 1.82×10^-6, 1.67×10^-6 and 1.44×10^-6 mol·L^-1, respectively. Therefore, a promising direct and simultaneous electrochemical determination method of multi-component phenolic pollutants in wastewater samples was constructed successfully on BDD electrode with advantages being rapid, simple, convenient, sensitive, in situ and inexpensive.     

Square‐Wave Voltammetry Determination of Aspartame in Dietary Products Using a Boron‐Doped Diamond Electrode

Abstract

The use of square‐wave voltammetry in conjunction with a cathodically pretreated boron‐doped diamond electrode for the analytical determination of aspartame in dietary products is described. In this determination, the samples were analyzed without previous treatment in a 0.5 mol l^?1 H₂SO₄ solution. A single oxidation peak at a potential of 1.6 V vs. Ag/AgCl (3.0 mol l^?1 KCl) with the characteristics of an irreversible reaction was obtained. The analytical curve was linear in the aspartame concentration range 9.9×10^?6 to 5.2×10^?5 mol l^?1 with a detection limit of 2.3×10^?7 mol l^?1. The relative standard deviation (n=5) obtained was smaller than 0.2% for the 1.0×10^?4 mol l^?1 aspartame solution. The proposed method was applied with success to the determination of aspartame in several dietary products and the results were similar to those obtained using an HPLC method at 95% confidence level.     

Determination of Antimony(III) by Differential Pulse Voltammetry Using a Gold Nanoparticle–Ionic Liquid–Graphene-Modified Selenium-Doped Carbon Paste Electrode

A simple and sensitive differential pulse stripping voltammetric method was developed for the determination of antimony(III) using a selenium-doped carbon paste electrode modified with an ionic liquid, graphene, and gold nanoparticles. The conditions, including the mass of graphene, concentration of hydrochloric acid, deposition potential, and deposition time were optimized by single-factor experiments. Under the optimal conditions, a linear equation of I_Sb(III) (µA)?=??16.9882???11.0929 c (µmol/L) (R?=?0.9965) and a detection limit of 2.7?×?10^?8?mol/L were obtained for 8.0?×?10^?8 to 4.8?×?10^?6?mol/L antimony(III). The response shows that the sensor enhances the sensitivity of antimony due to the high conductivity and large surface areas of the ionic liquid, graphene, and gold nanoparticles. This electrode may provide a new sensing platform for the determination of antimony.     

Voltammetric Determination of L‐Dopa Using a Carbon Nanotubes‐Nafion Modified Glassy Carbon Electrode

Abstract

A method for determination of L‐dopa by the adsorption stripping voltammetry (ASV) using a multiwalled carbon nanotubes (MWNTs)–Nafion modified glassy carbon electrode (GMGCE) was proposed. This chemically modified electrode (CME) shows a better stability. A sensitive oxidation peak was observed and the anodic peak potential is ca. 0.374V (vs. SCE). The influences of various experimental parameters on the current peak were completely studied. Under the optimized condition, the method has been applied to the determination of L‐dopa in samples. There is a good linear relationship between the peak current (i_p) and L‐dopa concentration in the range of 3.5×10^?7～1.5×10^?5 mol/L, with the limit of detection 5.0×10^?8 mol/L.     

Capillary Electrophoretic Determination of Jinggangmycin A in Formulations Using Direct UV Detection

A simple, fast and reliable method was developed for the analysis of jinggangmycin A （validamycin A） in commercial formulations. The running buffer used was acetate buffer （100 mmol/L, pH 4.7） with 15 kV as the applied voltage. The detection was achieved by using direct UV mode at 200 nm and the detection limit was 0.2 μg/mL. Linearity in the concentration range of 5-500 μg/mL was excellent （RE 〉 0.999）. The run-to-run repeatability （n = 3）, as expressed by the relative standard deviation （RSD） for migration times and peak areas were less than 0.5% and 3.0% respectively. The mean recovery ranged from 97.2% to 101.4%.     

Application of Internal Standard for Micro Extraction– Spectrophotometric Determination of Bismuth in Pharmaceutical Formulations

 A micro extraction – spectrophotometric procedure is developed for the determination of bismuth in pharmaceutical formulations. The procedure is based on the extraction of tetraiodobismuthate(III) ion paired with benzyltributylammonium cation into chloroform. The application of Nile Blue as internal standard (IS) enabled good analytical performance for micro-scale analysis. The ratio between the absorbances measured at 491 nm (bismuth complex) and at 632 nm (IS) was taken as the analytical signal. The procedure was carried out in Eppendorf tubes, lowering significantly the use of reagents and the volume of organic solvent. In the calibration range up to 60 mgċl⁻¹, the linear regression coefficient was 0.9999, the CV for 15 mgċl⁻¹ and for 50 mgċl⁻¹ Bi were 1.6% and 0.7% respectively. The results obtained in the analysis of pharmaceutical formulations were in good agreement with the results of EDTA titration method. Received November 25, 1999. Revision February 14, 2000.     

Determination of Tetracycline in Bovine and Breast Milk Using a Graphite–Polyurethane Composite Electrode

A bare graphite–polyurethane composite electrode (60% graphite, m/m) was used for the determination of tetracycline in bovine and breast milk. Limits of detection as low as 2.6?µmol?L^?1 were obtained in pH 2.3 phosphate buffer using optimized differential pulse voltammetric parameters at the graphite–polyurethane composite electrode. The milk treatment consisted of acidification with 80% trichloroacetic acid, centrifugation to remove solid phase from milk, the isolation of the antibiotic from the whey using solid-phase extraction, and direct analysis in pH 2.3 phosphate buffer. Recoveries between 83 and 99% and 97% were obtained for tetracycline fortified in bovine and breast milk, suggesting that this approach is a promising screening procedure.     

High‐Performance Liquid Chromatographic Determination of Parecoxib in Human Plasma and Pharmaceutical Formulations

Abstract

A simple and sensitive RP‐HPLC method for the determination of parecoxib (PXB) in human plasma and pharmaceutical formulations has been developed and validated. The separation of PXB and the internal standard, ibuprofen (IBF) was achieved on a CLC C₁₈ (5 μ, 25 cm×4.6 mm i.d.) column using UV detector at 200 nm. The mobile phase consisted of acetonitrile‐water (92:8 v/v). The linear range of detection was found to be 0.9–18.4 µg/ml (r=0.9985). Intra‐ and inter‐day assay relative standard deviations were observed to be less than 0.3%. The method has been applied successfully for the determination of PXB in spiked human plasma and pharmaceutical preparations. Analytical parameters were calculated and complete statistical evaluation is incorporated.     

Electrochemical Oxidation of Phenothiazine Derivatives at Glassy Carbon Electrodes and Their Differential Pulse and Square‐wave Voltammetric Determination in Pharmaceuticals

Abstract

Three 2,10‐disubstituted phenothiazines—chlorpromazine hydrochloride (CPM), thioridazine hydrochloride (TR) and propericiazine (PRC)—were electrochemically studied in various buffer systems at different pH values, using a glassy carbon electrode. The substances were electrochemically oxidized at potential range 0.55–0.75 V. The oxidation was reversible and exhibited diffusion‐controlled process. The mechanism of the oxidation process is discussed. According to the linear relation between peak current and concentration, differential pulse voltammetry (DPV) and square wave voltammetry (SWV) methods for quantitative determination of chlorpromazine and propericiazine in 0.1 M HClO₄, and thioridazine in pH 2 phosphate buffer, was applied. Both the repeatability and reproducibility of the methods were also determined for all studied substances. The developed procedures were successfully applied to the determination of chlorpromazine and thioridazine in pharmaceutical dosage forms.     

High‐Performance Liquid Chromatography Determination of Latanoprost in Pharmaceutical Formulations using UV Detection

Abstract

A simple, fast, and accurate high‐performance liquid chromatography (HPLC) method was developed to determine latanoprost in pharmaceutical formulations. The drug was chromatographed on a C₁₈ column. Eluents were monitored at a wavelength of 210 nm using a mixture of acetonitrile and 0.05 M potassium phosphate buffer pH 3.0 (70:30, (v/v). A linear response (r>0.9998) was observed in the range of 10.0–90.0 µg mL^?1. The method showed good recoveries (average 100.4%) and the relative standard deviations intra‐ and inter‐day were ≤1.0%. The method can be used for quality control assay of latanoprost in raw materials as well as in pharmaceutical formulations.     

Determination of Mercury Using a Novel Sonogel‐Carbon 3‐Methylthiophene Electrode

Abstract

A solid Sonogel‐Carbon electrode was modified for the determination of Hg (II) in industrial waste water. 3‐Methylthiophene (3MT), pyrrol, poly‐3‐methylthiophene (P3MT), polypyrrol, and C18 were used for the chemical modification. The obtained composite electrodes were tested for their response to Hg(II); the best results were observed for the 3MT monomer modification with a detection limit of 10^?2 mg · l^?1 and 3 weeks lifetime of use. A linear relationship between anodic peak height and concentration inside the range of 0.07–0.42 mg · l^?1 was obtained. A study of interferences due to other heavy metal is also included.     

Voltammetric Determination of Bisphenol A Using an Acetylene Black‐Dihexadecyl Hydrogen Phosphate Composite Film‐Modified Electrode

Abstract

Herein, acetylene black (AB) was easily dispersed into water in the presence of dihexadecyl hydrogen phosphate (DHP), resulting in a stable and homogeneous AB‐DHP suspension. Then, an AB‐DHP composite film coated glassy carbon electrode (GCE) was constructed after evaporation of water. The electrochemical behavior of bisphenol A was investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV). Compared with the unmodified GCE, the AB‐DHP film‐modified GCE not only significantly enhances the oxidation peak current of bisphenol A but also lowers the oxidation overpotential, suggesting that AB‐DHP film‐modified GCE has great potential in sensitive determination of bisphenol A. Based on this, a sensitive and simple electrochemical method was developed after optimization of the experimental parameters such as supporting electrolyte, the amount of AB‐DHP, scan rate, and accumulation time. The linearity is over the range form 2.0×10^?8 to 5.0×10^?6 mol l^?1, and the detection limit is 6.0×10^?9 mol l^?1. Finally, this method was successfully employed to determine bisphenol A in waste water samples.     

Anodic Stripping Voltammetric Determination of Lead(II) Using Glassy Carbon Electrode Modified with Novel Calix[4]arene

Owingtothegrowingawarenessofleadpollutionandtoxicity,manytechniquesarecurrentlyemployedforthedeterminationoftracePbioninenvironmentalsamples .1Amongthem ,thedevelopmentofchemicallymodifiedelectrodes (CMEs)andapplicationsofanodicstrippingvoltammetry (ASV)havereceivedconsiderableattention .CMEsarecharacterizedbypurposefullyalteringtheirsur facecharacteristicstodisplaynewqualitiesthatcouldbeexploitedforanalyticalapplications .Thesekindsofelec trodesareinexpensiveandpossessmanyadvantagessuchas…     

RP‐HPLC Method for the Determination of Tenofovir in Pharmaceutical Formulations and Spiked Human Plasma

Abstract

A simple reverse‐phase high‐performance liquid chromatographic method for the determination of tenofovir disoproxil fumarate (TDF) in pharmaceutical formulations and human plasma samples has been developed and validated. Piroxicam (PRX) was used as an internal standard. The assay of the drug was performed on a CLC C₁₈ (5 μ, 25 cm×4.6 mm i.d.) with UV detection at 259 nm. The mobile phase consisted of acetonitrile–water mixture in the ratio of 75∶25, and a flow rate of 1 ml/min was maintained. The standard curve was linear over the range of 0.2–10 µg/ml (r ²=0.9966). Analytic parameters have been evaluated. Within‐day and between‐day precision as expressed by relative standard deviation was found to be less than 2%. The method has been applied successfully for the determination of TDF in spiked human plasma samples and pharmaceutical formulations.     

Anodic Stripping Voltammetric Determination of Lead(II) with a 2‐Aminopyridinated‐Silica Modified Carbon Paste Electrode

Abstract

A carbon paste electrode modified with organically functionalized silica was used for the determination of lead. The measurements were carried out in three steps including an open circuit accumulation followed by electrolysis of accumulated lead at the carbon paste electrode and differential pulse voltammetric determination. The effects of several experimental variables such as carbon paste composition, pH and concentration of supporting electrolyte, electrolysis potential, and electrolysis time were studied. The resulting electrode demonstrates linear response over a wide range of Pb(II) concentration (5–1000 ng mL^?1) with an accumulation time of 60 sec. The effects of potential interfering ions were studied, and it was found that the proposed procedure is free from most interferences. Long lifetime and rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over at least 4 months. The prepared electrode was used for determination of lead spiked in a hair sample, and very good recovery results were obtained over a wide concentration range of lead.