Voltammetric Behavior of Mifepristone (RU‐486) Using Square‐Wave and Adsortive Stripping‐Wave Techniques. Determination in Urine Samples

The behavior of Mifepristone (RU‐486) was studied by square‐wave technique, leading to two methods for its determination in aqueous samples and urine samples at pH 2. The application of the square‐wave (SW) without the adsorptive accumulation and stripping voltammetric (AdSV) show the maximum response at ?0.896 V using an accumulation potential of ?0.5 V. The effect of experimental parameters that affect this determination are discussed. For the stripping technique, Mifepristone proved to be more sensitive, yielding signals four times larger than those obtained by applying a square‐wave scan without the previous accumulation. The calibration plot to determine Mifepristone was linear in the range 2.4×10^?8 and 5.4×10^?7 M by stripping mode with an accumulation time t_acc of 30 s. The relative standard deviation obtained for concentration levels of Mifepristone as low as 2.0×10^?7 M with square‐wave was 1.17% (n=10) and with stripping square‐wave 2.02% (n=10) in the same day. The two proposed methods (SW and SWAdSV) were applied to the determination of Mifepristone in urine.     

Square-wave adsorptive stripping voltammetric determination of antihypertensive agent telmisartan in tablets and its application to human plasma

The adsorptive stripping voltammetry of telmisartan was investigated with a hanging mercury drop electrode. This compound produced a catalytic hydrogen wave at ?1.5 V in Britton Robinson buffer of pH 10.38, and the peak current increased with adsorptive accumulation at the electrode. Adsorptive stripping voltammetry with the catalytic hydrogen wave could provide a sensitive novel method for the determination of telmisartan. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for telmisartan determination. Under these optimized conditions the square-wave adsorptive stripping voltammetric (SW-AdSV) peak current showed a linear dependence on drug concentration over the range 0.05–3.00 μg/mL (1 × 10^?7?6 × 10^?6 M) (r = 0.999) with accumulation for 120 s at ?1.0 V vs. Ag/AgCl. The proposed electrochemical procedure was successfully applied for the determination of telmisartan in pharmaceutical tablets and human plasma. The results of the developed SW-AdSV method were comparable with those obtained by reported analytical procedures.     

Determination of Melatonin Hormone in Bulk Form,Tablets and Human Serum by Square‐Wave Cathodic Adsorptive Stripping Voltammetry

Melatonin hormone plays an important role in many distinct physiological functions. A fully validated, sensitive and reproducible square‐wave cathodic adsorptive stripping voltammetric procedure was described for determination of melatonin in bulk form, tablets and human serum. The procedure was based on the reduction of the adsorptive hormone onto a hanging mercury drop electrode. Reduction behavior of melatonin was studied in both Britton‐Robinson (pH 2–11) and acetate (4.5–5.5) buffers. Acetate buffer of pH 5.0 was found reasonable as a supporting electrolyte for assay of the drug. The square‐wave cathodic adsorptive stripping voltammogram of melatonin showed a single well‐defined peak at ?1.45 V (vs. Ag/AgCl/KCl_s) using an accumulation potential of ?0.65 V. This peak may be attributed to the reduction of C?O double bond of the amide functional group of the reactant molecule. A mean recovery for 1×10^?8 M melatonin in bulk form followed 30 s accumulation of 98.87%±0.78 and a detection limit of 3.13×10^?10 M were achieved. The proposed procedure was successfully applied for the determination of the drug in tablets and human serum with mean recoveries of 97.68%±0.57 and 101.67%±0.85, respectively. A detection limit of 8.80×10^?10 M was achieved for the determination of the drug in human serum. Results of the proposed method were comparable and coincided with those obtained by reported method. Vitamin B₆ and common excipients, which are co‐formulated with melatonin, did not interfere. Also the effect of some interfering compounds such as serotonin, tryptophan and 5‐hydroxytryptophan on the determination of melatonin in human serum was studied, and all have no significant effect on the assay recovery.     

Electrochemical Determination of Citalopram by Adsorptive Stripping Voltammetry–Determination in Pharmaceutical Products

Abstract

The electrochemical behavior of citalopram was studied by square‐wave and square‐wave adsorptive‐stripping voltammetry (SWAdSV). Citalopram can be reduced and accumulated at a mercury drop electrode, with a maximum peak current intensity being obtained at a potential of approximately ?1.25 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 12. A SWAdSV method has been developed for the determination of citalopram in pharmaceutical preparations. The method shows a linear range between 1.0×10^?7 and 2.0×10^?6 mol L^?1 with a limit of detection of 5×10^?8 mol L^?1 for an accumulation time of 30 s. The precision of the method was evaluated by assessing the repeatability and intermediate precision, achieving good relative standard deviations in all cases (≤2.3%). The proposed method was applied to the determination of citalopram in five pharmaceutical products and the results obtained are in good agreement with the labeled values.     

An Electrochemical Sensor Based on Silver Nanoparticles‐Benzalkonium Chloride for the Voltammetric Determination of Antiviral Drug Tenofovir

A simple voltammetric nanosensor was described for the highly sensitive determination of antiviral drug Tenofovir. The benzalkonium chloride and silver nanoparticles were associated to build a nanosensor on glassy carbon electrode. Surface characterictics were achieved using scanning electron microscopic technique. The voltammetric measurements were performed in pH range between 1.0 and 10.0 using cyclic, adsorptive stripping differential pulse and adsorptive stripping square wave voltammetry. The linear dependence of the peak current on the square root of scan rates and the slope value (0.770) demonstrated that the oxidation of tenofovir is a mix diffusion‐adsorption controlled process in pH 5.70 acetate buffer. The linearity range was found to be 6.0×10⁻⁸–1.0×10⁻⁶ M, and nanosensor displayed an excellent detection limit of 2.39×10⁻⁹ M by square wave adsorptive stripping voltammetry. The developed nanosensor was successfully applied for the determination of Tenofovir in pharmaceutical dosage form. Moreover, the voltammetric oxidation pathway of tenofovir was also investigated at bare glassy carbon electrode comparing with some possible model compounds (Adenine and Adefovir).     

Electrochemical Determination and in silico Studies of Fludarabine on NH2 Functionalized Multiwalled Carbon Nanotube Modified Glassy Carbon Electrode

A sensitive voltammetric technique has been developed for the determination of Fludarabine using amine‐functionalized multi walled carbon nanotubes modified glassy carbon electrode (NH₂‐MWCNTs/GCE). Molecular dynamics simulations, an in silico technique, were employed to examine the properties including chemical differences of Fludarabine‐ functionalized MWCNT complexes. The redox behavior of Fludarabine was examined by cyclic, differential pulse and square wave voltammetry in a wide pH range. Cyclic voltammetric investigations emphasized that Fludarabine is irreversibly oxidized at the NH₂‐MWCNTs/GCE. The electrochemical behavior of Fludarabine was also studied by cyclic voltammetry to evaluate both the kinetic (k_s and E_a) and thermodynamic (ΔH, ΔG and ΔS) parameters on NH₂‐MWCNTs/GCE at several temperatures. The mixed diffusion‐adsorption controlled electrochemical oxidation of Fludarabine revealed by studies at different scan rates. The experimental parameters, such as pulse amplitude, frequency, deposition potential optimized for square‐wave voltammetry. Under optimum conditions in phosphate buffer (pH 2.0), a linear calibration curve was obtained in the range of 2×10^?7 M–4×10^?6 M solution using adsorptive stripping square wave voltammetry. The limit of detection and limit of quantification were calculated 2.9×10^?8 M and 9.68×10^?8 M, respectively. The developed method was applied to the simple and rapid determination of Fludarabine from pharmaceutical formulations.     

Simultaneous Determination of Antimony and Lead in Gunshot Residue by Cathodic Adsorptive Stripping Voltammetric Methods

Differential pulse cathodic adsorptive stripping (DPCAdSV) and square wave cathodic adsorptive stripping (SWCAdSV) voltammetric methods were developed for the determination of antimony and lead in gunshot residues. Linear working ranges for DPCAdSV and SWCAdSV methods were (2.0×10^?9–5.0×10^?7) M and (2.0×10^?9–7.0×10^?7) M for antimony and 2.0×10^?9–3.0×10^?7 M (both methods) for lead. The detection of antimony limits were found to be 1.3×10^?9 M for DPCAdSV and 7.3×10^?10 M for SWCAdSV while the corresponding values for lead were 3.0×10^?9 M and 5.8×10^?10 M. Antimony and lead contents obtained by these methods in gunshot residues are in good agreement with those obtained by graphite furnace atomic absorption spectrometric method within a confidence limit of 95%.     

Voltammetric Determination of Acibenzolar‐S‐Methyl Using a Renewable Silver Amalgam Film Electrode

Acibenzolar‐S‐methyl (ASM) is a novel fungicide applied for crop protection. A renewable silver amalgam film electrode was used for the determination of ASM in pH 3.4 Britton? Robinson buffer using square wave adsorptive stripping voltammetry (SW AdSV). The parameters of the method were optimized. The electroanalytical procedure made possible to determine ASM in the concentration range of 5×10^?8–3×10^?7 mol L^?1 (LOD=4.86×10^?9, LOQ=1.62×10^?8 mol L^?1). The effect of common interfering pesticides and heavy metal ions was checked. The validated method was applied in ASM determination in spiked water samples.     

Development of a Diamond Nanoparticles-based Nanosensor for Detection and Determination of Antiviral Drug Favipiravir

This study developed a nanosensor for the detection and determination of favipiravir, a presumed drug that has potential therapeutic efficacy in treating COVID-19 patients, from tablets and serum samples. This nanosensor was obtained by adding the optimum amount of diamond nanoparticles into carbon paste. For the determination of favipiravir adsorptive stripping differential pulse (AdSDPV) and adsorptive stripping square wave voltammetry (AdSSWV) were used. Limit of detection values were found as 4.83×10⁻⁹ M and 2.44×10⁻⁷ M for bulk and 5.18×10⁻⁸ M and 4.38×10⁻⁸ M for serum samples using AdSDPV and AdSSWV, respectively. Recovery studies made of the tablet and serum produced satisfactory results.     

Determination of Chlorfenvinphos in Soils by Microwave‐Assisted Extraction and Stripping Voltammetry with an Ultramicroelectrode

Abstract

A methodology for the determination of the pesticide chlorfenvinphos by microwave‐assisted solvent extraction and square‐wave cathodic stripping voltammetry at a mercury film ultramicroelectrode in soil samples is proposed. Optimization of microwave solvent extraction performed with two soils, selected for having significantly different properties, indicated that the optimum solvent for extracting chlorfenvinphos is hexane‐acetone (1∶1, v/v). The voltammetric procedure is based on controlled adsorptive accumulation of the insecticide at the potential of?0.60 V (vs. Ag/AgCl) in the presence of Britton‐Robinson buffer (pH 6.2). The detection limit obtained for a 10 s collection time was 3.0×10^?8 mol l^?1. The validity of the developed methodology was assessed by recovery experiments at the 0.100 µg g^?1 level. The average recoveries and standard deviations for the global procedure reached by MASE‐square‐wave voltammetry were 90.2±2.8% and 92.1±3.4% for type I (soil rich in organic matter) and type II (sandy soil) samples, respectively. These results are in accordance to the expected values which show that the method has a good accuracy.     

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.     

A Validated Voltammetric Procedure for Quantification of the Antifungal Drug Griseofulvin in Bulk Form,Tablets, and Biological Fluids at a Mercury Electrode

Abstract

Griseofulvin is an antifungal antibiotic used to treat various pathogenic mycotic diseases. The voltammetric behavior of griseofulvin at a hanging mercury drop electrode in Britton‐Robinson buffers of pH 2–11.5 was studied and discussed. A fully validated sensitive square‐wave adsorptive cathodic stripping voltammetric procedure was described for direct determination of bulk griseofulvin substance. The procedure was based on the reduction of the >C?O double bond of griseofulvin molecule following its preconcentration onto a hanging mercury drop electrode in a Britton‐Robinson buffer of pH 10. Limits of detection (LOD) and quantitation (LOQ) of 5.8×10^?10 M and 1.93×10^?9 M bulk griseofulvin were achieved, respectively. The proposed stripping voltammetric procedure was successfully applied to assay griseofulvin in tablets and in spiked human serum and urine samples. LOD of 8.65×10^?10 M and 6.6×10^?9 M and LOQ of 2.88×10^?9 M and 2.2×10^?8 M griseofulvin in spiked human serum and urine samples, respectively, were achieved.     

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.     

Sequential Voltammetric Determination of Uranium,Cadmium and Lead by Using the ex situ Bismuth Film Electrode: Application to Phosphate Fertilizers

A sequential voltammetric procedure for the determination of uranium, cadmium and lead was investigated at an ex situ bismuth film electrode (BiFE). First, the adsorptive stripping voltammetry was applied to assay the U(VI)‐cupferron complex in the differential pulse mode (detection limit of 1.0 µg L^?1, 200 s accumulation time). Through the manipulation of the same aliquot of the sample, efforts were made to quantify cadmium and lead by square wave anodic stripping voltammetry. Detection limits of 2.03 µg L^?1 for Cd (II) and 2.43 µg L^?1 for Pb (II) were calculated (100 s accumulation time). The methodology was successfully applied to phosphate fertilizer samples after open vessel wet decomposition (HNO₃/H₂O₂). The following value ranges were evaluated: U (VI) 37.2–150 mg kg^?1, Pb (II) 78.3–204 mg kg^?1 and Cd (II) 44.1–71.6 mg kg^?1. Validation was performed by using the standard reference materials SRM‐695 – phosphate fertilizer – and SRM‐1643e – water.     

Electrochemical Behavior of 8‐Azaguanine at DNA Langmuir–Blodgett Modified Glassy Carbon Electrode and Its Analytical Application

A highly sensitive electrochemical biosensor for the detection of trace amounts of 8‐azaguanine has been designed. Double stranded (ds)DNA molecules are immobilized onto a glassy carbon electrode surface with Langmuir–Blodgett technique. The adsorptive voltammetric behaviors of 8‐azaguanine at DNA‐modified electrode were explored by means of cyclic voltammetry and square wave voltammetry. Compared with bare glassy carbon electrode (GCE), the Langmuir–Blodgett film modified electrode can greatly improve the measuring sensitivity of 8‐azaguanine. Under the optimum experimental conditions, the Langmuir–Blodgett film modified electrode in pH 3.0 Britton–Robinson buffer solutions shows a linear voltammetric response in the range of 5.0×10^?8 to 1.0×10^?5 mol L^?1 with detection limit 9.0×10^?9 mol L^?1. The method proposed was applied successfully for the determination of 8‐azaguanine in diluted human urine with wonderful satisfactory.     

Square Wave Cathodic Adsorptive Stripping Voltammetric Determination of the Anticancer Drugs Flutamide and Irinotecan in Biological Fluids Using Renewable Pencil Graphite Electrodes

A sensitive electrochemical method based on square wave cathodic adsorptive stripping voltammetry (SWCASV) using pencil graphite electrodes (PGE) was developed for the individual and simultaneous determination of the anticancer drugs flutamide (Flu) and irinotecan (Irino) in biological fluids. Calibration curves showed an excellent linear response with limits of detection of 1.68×10^?9 and 1.55×10^?8 M Irino and Flu, respectively. The statistical evaluation of within‐day repeatability (n=5) and day to day precision (n=5) showed satisfactory accuracy and precision. SWCASV using a PGE for individual and simultaneous determination of both drugs in bulk form, human urine and serum samples was demonstrated.     

Adsorptive stripping voltammetry of sex hormones at the static mercury drop electrode

Controlled adsorptive accumulation of testosterone, methyltestosterone and progesterone on the static mercury drop electrode provides the basis for direct stripping measurement of these compounds ar nanomolar concentrations. The adsorptive stripping behavior is evaluated with respect to preconcentration time and potential, stripping mode, concentration dependence, drop size and other variables. With 5-min accumulation, peak current enhancements of 45, 18 anal 12 are observed for 5 × 10^?8 M testosterone, progesterone and methyltestosterone, respectively, relative to direct pulse voltammetry. Detection limits are 1.6 × 10^?10 M for testosterone, 2 × 10^?10 M for progesterone and 3.3 × 10^?10 M for methyltestosterone with 15-min preconcentration. The relative standard deviation for 8 × 10^?8 M progesterone is 3.4% (n=8). Applicability to direct measurements of methyltestosterone in pharmaceutical formulations is assessed.     

Voltammetric Determination of Selected Aminoquinolines Using Carbon Paste Electrode

Optimum conditions have been found for voltammetric determination of mutagenic 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline by differential pulse voltammetry and adsorptive stripping differential pulse voltammetry on carbon paste electrode. The lowest limits of determination were found for adsorptive stripping differential pulse voltammetry in 0.1 mol dm^?3 H₃PO₄ (5×10^?7 mol dm^?3 , 1×10^?7 mol dm^?3, and 1×10^?7 mol dm^?3 for 5‐aminoquinoline, 6‐aminoquinoline and 3‐aminoquinoline, respectively). The possibility to determine mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 5‐aminoquinoline or 6‐aminoquinoline, and mixtures of 5‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline by differential pulse voltammetry was verified. Binary mixtures of 8‐aminoquinoline with 3‐aminoquinoline or 6‐aminoquinoline, and of 3‐aminoquinoline with 5‐aminoquinoline could be successfully analyzed.     

Study on the Electrochemical Behavior of Melatonin with an Activated Electrode

It was found that melatonin could be incorporated and accumulated on the surface of the glassy carbon electrode which was activated electrochemically by pretreatment in sodium hydroxide solution by means of cycling the potential well into the positive limit of the solvent. In Britton‐Robinson buffer solution (pH 6.7), melatonin gave a sensitive oxidation wave at a potential of +0.65 V (vs.Ag/AgCl) by using Osteryoung square‐wave stripping voltammetry (OSWSV). The oxidation process has been shown to be irreversible and adsorption‐controlled at this electrode by means of cyclic voltammetry and linear sweep voltammetry. A chronocoulometric characterization of the adsorption characteristics of melatonin at this electrode is also presented. The factors affecting the peak current were optimized, and the dependence of peak currents on the concentration of melatonin was found to be linear in the range 8.0×10^?7?1.0×10^?5 mol L^?1. A detection limit of 5.0×10^?8 mol L^?1 was obtained (signal‐to‐noise ratio of 3). This method was applied to the assay of melatonin in tablets and capsules with good recoveries (98–100%).     

Simultaneous Determination of Thallium and Lead on a Chemically Modified Electrode with Langmuir– Blodgett Film of a p‐tert‐Butylcalix[4]arene Derivative

A new voltammetric sensor, Langmuir–Blodgett (LB) film of a p‐tert‐butylcalix[4]arene derivative modified glassy carbon electrode, was designed and successfully used in simultaneous determination of Tl⁺ and Pb²⁺ by square‐wave anodic stripping voltammetry. Under the optimum experimental conditions, this newly developed sensor reveal good linear response for Tl⁺ and Pb²⁺ in the concentration range of 3×10^?8–4×10^?6 mol L^?1 and 2×10^?7–2×10^?5 mol L^?1 respectively. The detect limits are 2×10^?8 mol L^?1 for Tl⁺ and 8×10^?8 mol L^?1 for Pb²⁺. Using proposed method, Tl⁺ and Pb²⁺ in environment samples were determined with satisfactory results.