The Determination of Nonelectroactive Anticancer Drug 6‐Thioguanine on DNA‐Modified Gold Electrode

Abstract

A nonelectroactive anticancer drug 6‐thioguanine was determined by differential pulse stripping voltammetry on the DNA‐modified gold electrode. The electrode was prepared by the dry adsorptive method, which is simple and direct. Potassium ferricyanate [K₃Fe(CN)₆] was chosen as an appropriate electroactive indicator to probe and characterize the interaction since the 6‐thioguanine and DNA both are nonelectroactive over the potential range studied. The reductive peak current of K₃Fe(CN)₆ is linear with the concentration of 6‐thioguanine in the range of 2.0×10^?8～8.0×10^?7 mol L^?1. The detection limit is 6.0×10^?9 mol L^?1. The established method was successfully applied to determining trace 6‐thioguanine with the recoveries between 95.7% and 105.6%.     

Determination of Atrazine in Natural Water Samples by Differential Pulse Adsorptive Stripping Voltammetry Using a Bismuth Film Electrode

A new method using differential pulse adsorptive stripping voltammetry for the determination of atrazine (ATZ) in natural water samples using a bismuth film electrode (BiFE) is proposed. The calibration curve was linear in the atrazine concentration range from 6.7×10^?7 to 2.0×10^?5 mol L^?1, with a limit of detection (LOD) of 1.4×10^?7 mol L^?1. The proposed electrode was applied for atrazine determination with satisfactory results compared with a high‐performance liquid chromatography method (HPLC).     

The cathodic stripping voltammetric determination of traces of iodide with a hanging copper amalgam drop electrode

A hanging copper amalgam drop electrode (HCADE) is used for the determination of traces of iodide by cathodic stripping voltammetry. The cathodic stripping peak of copper(I) iodide from the HCADE is better defined than that of mercury(I) iodide from a hanging mercury drop electrode. Optimum conditions and interferences are reported. With a 3-min deposition time at ?0.1 V vs. SCE, the calibration plot is linear up to 2 × 10^?6 mol dm^?3 iodide. The detection limit for iodide with the HCADE under voltammetric conditions is 4 × 10^?8 mol dm^?3; this is lowered to 8 × 10^?9 mol dm^?3 by using the differential pulse stripping technique.     

Square-Wave Cathodic Stripping Voltammetry of Marcellomycine. A Sensitive Analytical Method

Abstract

Square-wave adsorptive stripping voltammetry has been applied to the determination of a new cytostatic anthracyclinic compound, marcellomycine. 100-fold and 1000-fold increases of sensitivity have been found with regard to the differential pulse stripping voltammetry and differential pulse polarography respectively. The detection limit is fixed at 5 × 10^?9 M.     

Electrochemical Behavior of Carvedilol and Its Adsorptive Stripping Determination in Dosage Forms and Biological Fluids

Carvedilol is used in the management of hypertension and angina pectoris and as an adjunct to standard therapy in symptomatic heart failure. The electrochemical oxidation of carvedilol was investigated using cyclic, linear sweep voltammetry at a glassy carbon electrode. In cyclic voltammetry, in all values of pH, the compound shows two irreversible oxidation peaks. These two peaks are related to the different electroactive part of the molecule. First and second peak currents were found as diffusion and adsorption controlled, respectively. Using second oxidation step, two voltammetric methods were described for the determination of carvedilol by differential pulse adsorptive stripping voltammetry (AdSDPV) and square‐wave adsorptive stripping voltammetry (AdSSWV) at a glassy carbon electrode. Accumulation of carvedilol was found to be optimized in 0.2 M H₂SO₄ solution following 275 second accumulation time at open circuit condition. Under optimized conditions, the current showed a linear dependence with concentration in the range between 2×10^?7 M and 2×10^?5 M in supporting electrolyte and in the range between 2×10^?7 M and 1×10^?5 M in spiked human serum samples for both methods. These methods were successfully applied for the analysis of carvedilol pharmaceutical dosage forms and spiked human serum samples. The repeatability and reproducibility of the methods for all media were determined. Precision and accuracy were also found. No electroactive interferences from the tablet excipients and endogenous substances from biological material were found.     

Fabrication of Bismuth/Multi-walled Carbon Nanotube Composite Modified Glassy Carbon Electrode for Determination of Cobalt

A bismuth/multi‐walled carbon nanotube (Bi/MWNT) composite modified electrode for determination of cobalt by differential pulse adsorptive cathodic stripping voltammetry is described. The electrode is fabricated by potentiostatic pre‐plating bismuth film on an MWNT modified glassy carbon (GC) electrode. The Bi/MWNT composite modified electrode exhibits enhanced sensitivity for cobalt detection as compared with the bare GC, MWNT modified and bismuth film electrodes. Numerous key experimental parameters have been examined for optimum analytical performance of the proposed electrode. With an adsorptive accumulation of the Co(II)‐dimethylglyoxime complex at ?0.8 V for 200 s, the reduction peak current is proportional to the concentration of cobalt in the range of 4.0×10^?10?1.0×10^?7 mol/L with a lower detection limit of 8.1×10^?11 mol/L. The proposed method has been applied successfully to cobalt determination in seawater and lake water samples.     

Electrochemical determination of muscle relaxant drug tetrazepam in bulk form,pharmaceutical formulation,and human serum

Tetrazepam dissolved in the Britton-Robinson universal buffer of various pH values (2.5–11.5) containing 10 vol. % of ethanol was reduced at the mercury electrode in a single 2-electron irreversible step due to reduction of the 4,5 C=N double bond of the seven-membered ring. Differential pulse polarography (DPP) and adsorptive cathodic stripping voltammetry (AdCSV) techniques (Linear sweep LS, differential pulse DP and square-wave SW modes) for quantification of tetrazepam in bulk form and in myolastan tablets are presented. Moreover, the described linear sweep, differential pulse, and square-wave adsorptive cathodic stripping voltammetry was successfully applied in quantification of tetrazepam in spiked human serum without any prior extraction of the drug. The obtained results showed an increased sensitivity of the described electro-analytical procedures for the quantification of tetrazepam in the following order DPP, DP-AdCSV, LS-AdCSV, and SW-AdCSV, since the observed limits of tetrazepam quantitation by these electroanalytical techniques were 5 × 10⁻⁶ mol L⁻¹, 3 × 10⁻⁷ mol L⁻¹, 1 × 10⁻⁸ mol L⁻¹, and 3 × 10⁻⁹ mol L⁻¹, respectively.     

Voltammetric Determination of 3‐Nitrofluoranthene and 3‐Aminofluoranthene at Boron Doped Diamond Thin‐Film Electrode

The voltammetric behavior of 3‐nitrofluoranthene and 3‐aminofluoranthene was investigated in mixed methanol‐water solutions by differential pulse voltammetry (DPV) at boron doped diamond thin‐film electrode (BDDE). Optimum conditions have been found for determination of 3‐nitrofluoranthene in the concentration range of 2×10^?8–1×10^?6 mol L^?1, and for determination 3‐aminofluorathnene in the concentration range of 2×10^?7–1×10^?5 mol L^?1, respectively. Limits of determination were 3×10^?8 mol L^?1 (3‐nitrofluoranthene) and 2×10^?7 mol L^?1 (3‐aminofluoranthene).     

Investigations on Bioanalytical Chemistry Part I. On Differential Pulse Voltammetry of Bilirubin

Abstract

The electrochemical behaviour of the bilirubin in many kinds of supporting electrolytes on a glassy carbon electrode (GCE) and a hanging mercury drop electrode (HMDE) was investigated by means of anodic or cathodic differential pulse voltammetry. The influences of different methods of pre-treatment of the glassy carbon electrode was also discussed. In Na₂B₄.O₇-KH₂PO₄ buffer solution, the linear range was 2×10^?9-1×10^?9 mol/l and the detection limit was 3.3×10^?9 mol/l by anodic differential pulse voltammetry at GCE. A linear relationship holds between the peak current and the concentration of bilirubin in a concentration range of 1×10^?9-4×10^?7 mol/l with good precision and accuracy, and the limit of detection was 2×10^?10 mol/l, when cathodic differential pulse adsorption voltammetry at HMDE was used.     

Direct Determination of Paracetamol in Environmental Samples Using Screen‐printed Carbon/Carbon Nanofibers Sensor – Experimental and Theoretical Studies

The paper describes the first electrochemical method (differential pulse adsorptive stripping voltammetry, DPAdSV) using a screen‐printed sensor with a carbon/carbon nanofibers working electrode (SPCE/CNFs) for the direct determination of low (real) concentrations of paracetamol (PA) in environmental water samples. By applying this sensor together with DPAdSV, two linear PA concentration ranges from 2.0×10^?9 to 5.0×10^?8 mol L^?1 (r=0.9991) and 1.0×10^?7–2.0×10^?6 mol L^?1 ( r=0.9994) were obtained. For the accumulation time of 90 s, the limit of detection was 5.4×10^?10 mol L^?1. Moreover, the SPCE/CNFs sensor and the DPADSV procedure for PA determination are potentially applicable in field analysis. The process of PA adsorption at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and theoretical studies. In the theoretical study of the interaction of CNF and PA, the first species was modelled by graphene‐like clusters containing up to 37 rings. It was found that the preferable orientation of PA is parallel to the carbon surface with the binding energy of about ?68 kJ/mol calculated by symmetry‐adapted perturbation theory (SAPT). Both the selectivity and the accuracy of the developed sensor for real sample analysis were also investigated using Polish river and sea samples.     

Electrochemical Behavior of 6-Mercapto-Purine at Hanging Copper Amalgam Dropping Electrode and Its Trace Determination by Differential Pulse Adsorption Cathodic Stripping Voltammetry

Abstract

The electrochemical behavior of 6-MP was studied by cyclic voltammetry at a hanging copper amalgam dropping electrode (HCADE). It was found that 6-MP could form a complex with the Cu(II) stripped from the HCADE, showing a new peak at ?0.19V in the medium of 0.1mol/L LiClO₄-0.5mol/L HClO₄ solution. The mechanism of the reaction was proposed. This new peak was sensitive and could be used for the determination of trace 6-MP by differential pulse adsorption cathodic stripping voltammetry (DPAdCSV). The linear range was from 3.6×10^?10 to 5.3×10^?6 mol/L, and the detection limit was about 1.2×10^?10 mol/L (S/N=3). The method was also successfully applied to the determination of 6-MP in pharmaceutical tablets.     

Sensitive and Simple Electrochemical Detection of Lead(II) with Carbon Ionic Liquid Electrode

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid 1‐ethyl‐3‐methylimidazolium ethylsulphate ([EMIM]EtOSO₃) as the modifier and further used as the working electrode for the sensitive anodic stripping voltammetric detection of Pb²⁺. The characteristics of the CILE were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In pH 4.5 NaAc‐HAc buffer Pb²⁺ was accumulated on the surface of CILE due to the extraction effect of IL and reduced at a negative potential (‐1.20 V). Then the reduced Pb was oxidized by differential pulse anodic stripping voltammetry with an obvious stripping peak appeared at ?0.67 V. Under the optimal conditions Pb²⁺ could be detected in the concentration range from 1.0 × 10^?8 mol/L to 1.0 × 10^?6 mol/L with the linear regression equation as I_p(μA) = ?0.103 C (μmol/L) + 0.0376 (γ = 0.999) and the detection limit as 3.0 × l0^?9 mol/L (3σ). Interferences from other metal ions were investigated and Cd²⁺ could be simultaneously detected in the mixture solution. The proposed method was further applied to the trace levels of Pb²⁺ detection in water samples with satisfactory results.     

Adsorptive stripping voltammetry of chlordiazepoxide at the hanging mercury drop electrode

Controlled adsorptive accumulation at the hanging mercury drop electrode enables 0.8–11 × 10^?5 M chlordiazepoxide to be quantified by differential-pulse stripping voltammetry with accumulation times of 1–3 min. With 3-min accumulation, the peak current is enhanced 12-fold for 1.0 × 10^?7 M chlordiazepoxide compared to the current from differential pulse polarography. The detection limit is 0.9 × 10^?9 M for 4-min accumulation. The procedure is applied to spiked human serum after preseparation of the drug on a Sep-Pak C₁₈ cartridge.     

Voltammetric Characterisation of Anticancer Drug Irinotecan

Electrochemical reduction of irinotecan was investigated on a static mercury drop electrode using square‐wave voltammetry. The mechanism of irinotecan electroreduction is a complex, pH‐dependent, quasireversible process and includes the transfer of two electrons and two protons. In acidic medium, the first electron transfer reaction is followed by the chemical reaction, and the product of this chemical reaction undergoes further electrochemical reduction at more negative potentials. Both irinotecan and the product of its reduction adsorb on the mercury electrode surface. Based on the adsorptive character of irinotecan, a new adsorptive stripping square‐wave voltammetric method for its electroanalytical determination has been proposed. The voltammetric response could be used to determine irinotecan in the concentration range from 1×10⁻⁷ mol/L to 1.5×10⁻⁶ mol/L and from 5×10⁻⁹ mol/L to 1.2×10⁻⁷ mol/L, if the accumulation time is 20 s and 300 s, respectively. The calculated limit of detection for irinotecan was found to be 8.7×10⁻⁹ mol/L (if t_acc=300 s).     

Catalytic Adsorptive Stripping Voltammetry of Molybdenum: Redox Kinetic Measurements

The electrode mechanism of Mo(VI) reduction was studied under catalytic adsorptive stripping mode by means of square‐wave voltammetry (SWV). Mo(VI) creates a stable surface active complex with mandelic acid. The electrode reaction of Mo(VI)‐mandelic acid system undergoes as one‐electron reduction, exhibiting properties of a surface electrode process. In the presence of chlorate, bromate, and hydrogen peroxide, the electrode reaction is transposed into a catalytic mechanism. The experimental results are compared with the recent theory for surface catalytic reaction, enabling qualitative characterization of the electrode mechanism in the presence of different catalytic agents. Utilizing both the method of “split SW peaks” and “quasireversible maximum” the standard redox rate constant of Mo(VI)‐mandelic acid system was estimates as k_s=150±5 s^?1. By fitting the experimental and theoretical results, the following catalytic rate constants have been estimated: (8.0±0.5)×10⁴ mol^?1 dm³ s^?1, (1.0±0.1)×10⁵ mol^?1 dm³ s^?1, and (3.2±0.1)×10⁶ mol^?1 dm³ s^?1, for hydrogen peroxide, chlorate, and bromate, respectively.     

Selective and Sensitive Determination of Uranyl Ions in Complex Matrices by Ion Imprinted Polymers‐Based Electrochemical Sensor

We report on the design of a UO₂²⁺‐selective electrode based on the use of UO₂²⁺ imprinted polymer nanoparticles (IP‐NPs), and its application for the differential pulse adsorptive cathodic stripping voltammetry determination of uranyl ions. A carbon paste electrode was modified with the IP‐NPs, and differential pulse adsorptive cathodic stripping voltammetry was applied as the detection technique after open‐circuit sorption of UO₂²⁺ ions. The modified electrode responses to UO₂²⁺ was linear in the 0.1 µg L^?1 to 10 µg L^?1 and in the 0.01 mg L^?1 to 10 mg L^?1. The method detection limit of the sensor was 0.03 µg L^?1.     

Voltammetric studies on the interactions between camazepam metabolic series and human serum albumin. Determination of oxazepam using adsorptive stripping voltammetry

The behaviour of oxazepam in adsorptive stripping voltammetry was studied taking into account those conditions which have an influence on the accumulation step (electrolyte, pH, time, potential, drop size and stirring rate), rest time and stripping step (pulse amplitude and scan rate). Oxazepam can be determined at a hanging mercury drop electrode by differential-pulse voltammetry in 0.008 M Britton-Robinson buffer at pH 2.0 with a ?0.50 V accumulation potential. Its detection limit was found to be 3.6 × 10^?10 M (30-s accumulation) and the relative standard deviation for oxazepam concentrations in the range 2.8 × 10^?8?4.0 × 10^?7 M is lower than 2.8% (80-s accumulation). In addition, a procedure using adsorptive stripping voltammetry was developed to study the interactions occurring between human albumin and the camazepam metabolic series (camazepam, temazepam and oxazepam). The interactions decreased in the order temazepam ? oxazepam ? camazepam and the groups and structural modifications favouring interaction were determined.     

Application of Non‐Stop‐Flow Differential Pulse Voltammetry at a Tubular Detector of Silver Solid Amalgam for Electrochemical Determination of Lomustine (CCNU)

An application of the flow differential pulse voltammetry with tubular detector based on silver solid amalgam for determination of antineoplastic drug lomustine in pharmaceutical preparations is presented. The highest sensitivity was obtained in [0.10 mol dm^?3 MES; 2.00 mol dm^?3 NaCl; pH 6.0]:EtOH (9 : 1) with flow rate 0.50 mL min^?1, and the magnitude of the modulation amplitude ?0.070 V. The calibration dependence was linear in the range 1×10^?6–1 × 10^?4 mol dm^?3 (R²=0.999). The limit of detection was 1.5×10^?7 mol dm^?3. This method was successfully used for determination of lomustine in real samples of chemotherapy drug CeeNU Lomustine 40 mg.     

Underpotential Deposition Study and Determination of Bismuth on Gold Electrode by Using Voltammetry

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Electrocatalytic Determination of Ascorbic Acid at the Surface of 2,7‐Bis(ferrocenyl ethyl)fluoren‐9‐one Modified Carbon Paste Electrode

A chemically modified carbon paste electrode with 2,7‐bis(ferrocenyl ethyl)fluoren‐9‐one (2,7‐BFEFMCPE) was employed to study the electrocatalytic oxidation of ascorbic acid in aqueous solution using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The diffusion coefficient (D=1.89×10^?5 cm² s^?1), and the kinetic parameter such as the electron transfer coefficient, α (=0.42) of ascorbic acid oxidation at the surface of 2,7‐BFEFMCPE was determined using electrochemical approaches. It has been found that under an optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 300 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak currents show a linear dependence on the ascorbic acid concentration and linear analytical curves were obtained in the ranges of 8.0×10^?5 M–2.0×10^?3 M and 3.1×10^?5 M–3.3×10^?3 M of ascorbic acid with correlation coefficients of 0.9980 and 0.9976 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2δ) were determined to be 2.9×10^?5 M and 9.0×10^?6 M with cyclic voltammetry and differential pulse voltammetry, respectively. This method was also examined for determination of ascorbic acid in pharmaceutical preparations.