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.     

Electrochemical Behavior and Determination of Nicardipine

Abstract

The voltammetric behavior and measurement of nicardipine at the glassy carbon, carbon paste and hanging mercury drop electrodes are discussed. Cyclic voltammetry is used to elucidate the redox mechanism. Nicardipine is shown to adsorb on carbon electrodes, with the surface species retaining its electroactive characteristics. The adsorptive accumulation serves as a preconcentration step which improves the voltammetric measurement with respect to selectivity and sensitivity. Coupling this with a medium-exchange step eliminates interferences due to solution-phase electroactive species and permits direct measurement in urine. The inherent sensitivity of differential pulse voltammetry at the mercury electrode permits convenient measurement at the submicromolar level, with detection limit of 2 × 10^?8M. Amperometric detection for a flow injection system is illustrated.     

The Convenient Determination of Palladium at a Solid Electrode via Adsorptive Stripping Voltammetry at a Glassy Carbon Electrode Modified with a Random Array of Mercury Nanodroplets

The detection of palladium using adsorptive stripping voltammetry reported by Wang et al. (J. Wang, K. Varughese Anal. Chim. Acta 1987, 199, 185 [3]) at a hanging mercury drop electrode is extended to a more convenient solid electrode. To this end a random array of 3.5×10⁸ mercury nanodroplets per cm² (65 nm average diameter) was electrodeposited on a glassy carbon substrate. Adsorptive stripping voltammetry was performed using 2×10^?4 M dimethylglyoxime as a chelating agent for the Pd(II) ion, with accumulation at ?0.20 V vs. SCE for 120 s and a linear detection range of 5–150 μM was determined with a limit of detection of 1.6 μM.     

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.     

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.     

Electrochemical Characterization and Rapid Voltammetric Determination of Riluzole in Pharmaceuticals and Human Serum

The electrochemical oxidation of riluzole was investigated using cyclic and linear sweep voltammetry. Under optimized conditions, current and concentration showed linear dependence in Britton Robinson buffer at pH 3.00 for boron doped diamond and pH 3.00 phosphate buffers for glassy carbon electrodes. Differential pulse and square wave voltammetry were used for the determination of riluzole levels in serum samples and pharmaceutical formulations. The limit of detections were found as 5.25 × 10^?7 M and 8.26 × 10^?8 M for glassy carbon electrode and 1.78 × 10^?7 M and 8.42 × 10^?8 M for boron-doped diamond electrodes, in serum samples, using differential pulse and square wave methods, respectively.     

Adsorptive stripping voltammetry of electroactive organic compounds

Adsorptive stripping voltammetry at a hanging mercury drop electrode is described for various polarographically active compounds. Diazepam, nitrazepam, papaverine and aromatic nitro compounds can be determined at concentrations of 1 × 10^?9–1 × 10^?6 M with errors of 5–7%. The effects of changing accumulation potentials and times are considered. Interference by other surface-active agents may be removed by prior molecular exclusion chromatography.     

Electrocatalytic Oxidation and Determination of Norepinephrine at Poly(Cresol Red) Modified Glassy Carbon Electrode

A glassy carbon electrode (GCE) was modified with electropolymerized films of cresol red in pH 5.6 phosphate buffer solution (PBS) by cyclic voltammetry (CV). The modified electrode shows an excellent electrocatalytic effect on the oxidation of norepinephrine (NE). The peak current increases linearly with the concentration of NE in the range of 3×10^?6–3×10^?5 M by the differential pulse voltammetry. The detection limit was 2×10^?7 M. The modified electrode can also separate the electrochemical responses of norepinephrine and ascorbic acid (AA). The separation between the anodic peak potentials of NE and AA was 190 mV by the cyclic voltammetry. And the responses to NE and AA at the modified electrode were relatively independent.     

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.     

Determination of Copper at a Glassy Carbon Electrode Modified with Langmuir–Blodgett Film of p‐tert‐Butylthiacalix[4]arene

A new type of voltammetric sensor, Langmuir–Blodgett film of p‐tert‐butylthiacalix[4]arene modified glassy carbon electrode, was advanced and used for determining copper at trace levels by differential pulse stripping voltammetry. Calibration plot was found to be linear in the range of 2×10^?8 M to 5×10^?6 M; the detection limit was 2×10^?9 M. Possible recognition mechanism was also discussed. From determination of Copper in real samples (river, lake and tap water) it can be concluded that the method is rapid, sensitive in determining of copper and can be used in the analysis of natural water samples.     

Determination of the Anticancer Drug Sorafenib in Serum by Adsorptive Stripping Differential Pulse Voltammetry Using a Chitosan/Multiwall Carbon Nanotube Modified Glassy Carbon Electrode

Adsorptive stripping differential pulse voltammetry (AdSDPV) was applied to the assay of sorafenib in human serum sample. Cyclic voltammetry at a carbon based screen printed electrode (SPE) permitted to detect the irreversible oxidation of SOR with formation of a new compound reversibly oxidized at a lower potential. Quantitative assays were realized using a chitosan/carboxylic acid functionalized multiwalled carbon nanotube modified glassy carbon electrode in 0.1 M phosphate buffer pH 7.0 in the presence of 50 % methanol. The AdSDPV method provided two linear responses within the concentration ranges 1×10^?8–8×10^?8 M and 1×10^?7–8×10^?7 M in serum with LOQ and LOD of 3.2×10^?9 and 9.6×10^?10 of lower linear range, respectively. The recovery of sorafenib in spiked serum was 97.5 %.     

A Determination of 6-Mercaptopurine and 6-Thio-Guanine By Anodic Differential Pulse Voltammetry

Abstract

The anodic oxidation of 6-mercaptopurine and 6-thioguanine has been studied on a rotating and stationary disk electrode of glassy carbon, using d.c. and differential pulse potential program. Conditions have been found for determination of these substances by anodic differential pulse voltammetry on a rotating disk electrode, with a detection limit of about 2 × 10^?5 mol 1^?1.     

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine on the Tetrabromo‐p‐Benzoquinone Modified Carbon Paste Electrode

The electrochemical properties of hydrazine studied at the surface of a carbon paste electrode spiked with p‐bromanil (tetrabromo‐p‐benzoquinone) using cyclic voltammetry (CV), double potential‐step chronoamperometry and differential pulse voltammetry (DPV) in aqueous media. The results show this quinone derivative modified carbon paste electrode, can catalyze the hydrazine oxidation in an aqueous buffered solution. It has been found that under the optimum conditions (pH 10.00), the oxidation of hydrazine at the surface of this carbon paste modified electrode occurs at a potential of about 550 mV less positive than that of a bar carbon paste electrode. The electrocatalytic oxidation peak current of hydrazine showed a linear dependent on the hydrazine concentrations and linear analytical curves were obtained in the ranges of 6.00×10^?5 M–8.00×10^?3 M and 7.00×10^?6 M–8.00×10^?4 M of hydrazine concentration with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 3.6×10^?5 M and 5.2×10^?6 M by CV and DPV methods. This method was also used for the determination of hydrazine in the real sample (waste water of the Mazandaran wood and paper factory) by standard addition method.     

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.     

Quantitative Analysis of Irbesartan in Pharmaceuticals and Human Biological Fluids by Voltammetry

Abstract

A differential pulse (DP) and square wave (SW) voltammetric techniques were developed for the determination of irbesartan. The electrochemical behavior of irbesartan was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV) at the hanging mercury drop electrode (HMDE). Different parameters were tested to optimize the conditions of the determination. It was found that in the range of 8 × 10^?6–1 × 10^?4 M, the currents measured by both of methods presented a good linear property as a function of the concentration of irbesartan. In addition, validation parameters, such as reproducibility, sensitivity, and recovery were evaluated as well. The slope of the log Ip- log ν linear plot was 0.58 indicating the diffusion control for 0.5 M sulphuric acid without the need for separation or complex sample preparation, since there was no interference from the excipients and endogenous substances.

The methods were successfully applied to the analysis of irbesartan in the pharmaceutical tablet formulations and in human serum samples.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

Determination of azinphos-ethyl insecticide by adsorptive stripping voltammetry on the hanging mercury-drop electrode

The electrochemical characteristics of azinphos-ethyl (APE) have been determined by means of electrochemical techniques such as cyclic voltammetry (CV) and adsorptive stripping voltammetry (ASV) at a hanging mercury drop electrode (HMDE) over a wide range of pH from 2.0 to 8.0. The cyclic voltammograms demonstrate the adsorption of this compound at the mercury electrode. A systematic study of the various operational parameters that affect the stripping response was carried out by differential pulse voltammetry (DPV). With a preconcentration potential of −0.6 V and a 60 s preconcentration time, the limit of detection was 5.42 × 10⁻⁹ M, and the relative standard deviation (n = 5) was 2.7 % at concentration level of 6.45 × 10⁻⁷ M APE. The degree of interference from diverse ions and some other pesticides on the differential pulse stripping signal for APE was evaluated. Finally, the method was applied to the determination of APM in spiked soil, tap water, and treated wastewater. The text was submitted by the author in English.     

Anodic Oxidation of α‐Lipoic Acid at a Glassy Carbon Electrode and Its Determination in Dietary Supplements

Abstract

Direct electrochemistry of alpha‐lipoic acid (ALA) was performed at a glassy carbon electrode using cyclic, differential pulse and square wave voltammetry over a wide range of pH. The oxidation of ALA is an irreversible process, pH independent, and involves the charge transfer of one electron. The diffusion coefficient of ALA was calculated from the results obtained at pH 6.9 in 0.1 M phosphate buffer and was shown to be D ₀=1.1×10^?5 cm² s^?1. The limits of detection (LOD) and quantification (LOQ) calculated from the results obtained at this pH are 1.8 and 6.1 µM, respectively.

The lipoic acid content in two dietary supplements samples, a syrup containing ALA and capsules of ALA, has been determined directly at the glassy carbon electrode by differential pulse voltammetry using the standard addition method.     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

L‐Cysteine Voltammetry at a Carbon Paste Electrode Bulk‐Modified with Ferrocenedicarboxylic Acid

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of L ‐cysteine occurs at a potential about 200 mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, k_h were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L ‐cysteine showed a linear dependent on the L ‐cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10^?5 M–2.2×10^?3 M and 1.5×10^?5 M–3.2×10^?3 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 2.6×10^?5 M and 1.4×10^?6 M by CV and DPV methods.