Cathodic Adsorptive Stripping Voltammetric Determination of the Antitumor Drug Rutin in Pharmaceuticals, Human Urine, and Blood Serum

Cathodic adsorptive stripping voltammetry (CASV) was applied for the determination of rutin in pharmaceuticals, human urine, and blood serum. An electrochemical stripping procedure for trace measurements of rutin was developed based on the adsorption of the Cu²⁺-rutin complex on a hanging mercury drop electrode and applied to the quantification of the drug. Cyclic voltammetry was used to characterize the interfacial and redox behavior of the adsorbed Cu²⁺-rutin complex. Experimental and instrumental parameters for quantitative determination were optimized, and a detection limit of 4.9 × 10⁻⁹ mol · L⁻¹ in presence of Cu²⁺-ions for quantification of rutin under optimum conditions was derived. The sharp peak of the adsorbed Cu²⁺-rutin complex associated with an effective interfacial accumulation of this compound facilitates the determination of rutin in biological fluids with good recoveries. The degree of interference from potentially present metal ions and organic compounds on the CASV signal for Cu²⁺-rutin complex was evaluated.     

A Comprehensive Investigation of Interactions between Antipsychotic Drug Quetiapine and Human Serum Albumin Using Multi-Spectroscopic,Biochemical, and Molecular Modeling Approaches

Quetiapine (QTP) is a short-acting atypical antipsychotic drug that treats schizophrenia or manic episodes of bipolar disorder. Human serum albumin (HSA) is an essential transport protein that transports hormones and various other ligands to their intended site of action. The interactions of QTP with HSA and their binding mechanism in the HSA-QTP system was studied using spectroscopic and molecular docking techniques. The UV-Vis absorption study shows hyperchromicity in the spectra of HSA on the addition of QTP, suggesting the complex formation and interactions between QTP and HSA. The results of intrinsic fluorescence indicate that QTP quenched the fluorescence of HSA and confirmed the complex formation between HSA and QTP, and this quenching mechanism was a static one. Thermodynamic analysis of the HSA-QTP system confirms the involvement of hydrophobic forces, and this complex formation is spontaneous. The competitive displacement and molecular docking experiments demonstrated that QTP is preferentially bound to HSA subdomain IB. Furthermore, the CD experiment results showed conformational changes in the HSA-QTP system. Besides this, the addition of QTP does not affect the esterase-like activity of HSA. This study will help further understand the credible mechanism of transport and delivery of QTP via HSA and design new QTP-based derivatives with greater efficacy.     

Voltammetric Determination of Quercetin in Urine at Carbon Paste Electrode

Abstract

The electrochemical behavior of the quercetin (Q) at a carbon paste electrode (CPE) containing 15% paraffin oil is investigated. Square wave anodic stripping voltammetric (SWASV) was used to determine quercetin in the presence of 0.04 M phosphate buffer (pH ～4) containing 0.1 M KCl with 15 s accumulation time at 25±1°C. Under the optimal experimental conditions, the adsorbed form is oxidized irreversibly. The linear concentration ranged from 67.66 to 338.3 ppb quercetin. The detection limit of 6.77 ppb Q (r=0.9997), with 15 s accumulation time and the relative standard deviation of 0.45 (n=5) was calculated. The interferences of some metal ions and some amino acids were studied. The method was applied to the analysis of spiked urine, with recovery of 99.9±0.5, and the relative standard deviation of 3.2%. Results were compared with the reported methods.     

Electroanalytical Characteristics of Amisulpride and Voltammetric Determination of the Drug in Pharmaceuticals and Biological Media

The electrochemical oxidation of antipsychotic drug amisulpride (AMS) has been studied in pH range 1.8–11.0 at a stationary glassy carbon electrode by cyclic, differential pulse and square‐wave voltammetry. Two oxidation processes were produced in different supporting electrolyte media. Both of the oxidation processes were irreversible and exhibited diffusion controlled. For analytical purposes, very resolved voltammetric peaks were obtained using differential pulse and square‐wave modes. The linear response was obtained in the range of 4×10^?6 to 6×10^?4 M for the first and second oxidation steps in Britton‐Robinson buffer at pH 7.0 and pH 3.0 (20% methanol v/v), respectively, using both techniques. These methods were used for the determination of AMS in tablets. The first oxidation process was chosen as indicative of the analysis of AMS in biological media. The methods were successfully applied to spiked human serum, urine and simulated gastric fluid samples.     

Determination of Picogram-Levels of Acetylspiramycin in Human Urine and Serum by Flow Injection Chemiluminescence

A sensitive chemiluminescence method for the determination of acetylspiramycin is presented. It is based on the greatly enhancive effect of acetylspiramycin on the chemiluminescence reaction between luminol and hydrogen peroxide in the flow system. The increase in chemiluminescence intensity was linearly proportional to the acetylspiramycin concentration in the range from 10pg·mL^–1 to 2.0ng·mL^–1 (r²=0.9979). The detection limit was 3pg·mL^–1 (3). At a flow rate of 2.0mL·min^–1, the process of determination, including sampling and washing, could be performed in 0.5 min, and the relative standard deviations of seven replicates are less than 5.0%. The proposed method was applied successfully to the determination of acetylspiramycin in pharmaceutical preparations, human urine and serum without pre-treatment. It was found that the excretive ratio of acetylspiramycin reached its maximum 2.0 hours after having been administered orally, and the excretive ratio in 12.0 hours was 8.4.     

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.     

Micelle-Enhanced Spectrofluorimetric Method for the Determination of Antibacterial Trovafloxacin in Human Urine and Serum

A spectrofluorimetric method for the determination of trace amounts of the antibacterial trovafloxacin has been developed based on its native fluorescence in a micellar solution of sodium dodecyl sulfate (SDS). The wavelengths of excitation and emission were 270 nm and 410 nm, respectively. The optimised method allows the determination of 3.0–40.0 ng mL⁻¹ of trovafloxacin in 8 mM SDS solution and 0.1 M acetic acid-sodium acetate buffer solution (pH 5.5), with a relative standard deviation of 1.5% (for a level of 12.0 ng mL⁻¹) and a detection limit of 0.8 ng mL⁻¹. The method was applied to the determination of trovafloxacin in human urine and serum samples. It was validated using HPLC as a reference method. Recovery levels of the method reached 100% in all cases.     

Comparison of Voltammetric Techniques for Ammonia Sensing in Ionic Liquids

In electroanalytical chemistry, it is often observed that square wave voltammetry (SWV) and differential pulse voltammetry (DPV) are more sensitive techniques compared to linear sweep voltammetry (LSV), due to their method of sampling which minimises the charging current (non‐faradaic processes). In this work, a comparison of the three techniques (LSV, DPV and SWV) is performed for ammonia (NH₃) gas oxidation (a chemically and electrochemically irreversible redox process) in an ionic liquid over a concentration range of 10–100 ppm. Four different platinum electrodes are employed: a screen‐printed electrode (SPE), a thin‐film electrode (TFE), a microarray thin‐film electrode (MATFE) and a Pt microdisk electrode (μ‐disk). Calibration plots (current vs concentration) for all three different electrochemical techniques on all four surfaces showed excellent linearity with increased concentrations of NH₃ gas and relatively low limits of detection (LODs). On the larger mm‐sized surfaces (SPE and TFE), the current responses for LSV and SWV were quite similar, but DPV gave the lowest currents. Whereas for the smaller micron sized electrodes (MATFE and μ‐disk), currents were of the order LSV>SWV>DPV, with LSV being far superior to the pulse techniques. These findings suggest that the pulse techniques of SWV and DPV may not be the optimum methods, particularly on microelectrodes, for the detection of analytes such as ammonia in RTILs.     

Iron(III)‐mediated Electrochemical Detection of Levofloxacin in Complex Biological Samples

We report the design of an electrochemical sensor capable of detecting levofloxacin (LEVX) in complex biological samples. This detection strategy is simple, fast, and does not require sample pretreatment or electrode modification. Unlike previously developed electrochemical LEVX sensors that require direct oxidation of LEVX, the sensing mechanism is based on the complexation reactions between LEVX and iron(III), resulting in a concentration‐dependent decrease in the iron(III) reduction peak current and a shift in the peak potential. These changes are presumably attributed to the decrease in the concentration of uncomplexed Fe(III) in the solution. The concentration‐dependent change in both the current and potential can be used for quantification of LEVX in various samples, including 50 % synthetic urine and 25 % synthetic human saliva. The limit of detection was estimated to be in the range of 1.5 to 2.3 μM, concentrations that are much lower than the concentration of LEVX found in urine and saliva samples of patients administered this drug for conditions such as urinary tract infection. With further optimization, this sensing strategy could find applications in clinical pharmacokinetic studies.     

Polarographic Determination of Lovastatin in the Presence of H2O2 in Pharmaceuticals, Human Urine and Serum

The polarographic reduction and catalytic behavior of lovastatin are studied by polarography and cyclic voltammetry. The reduction wave of lovastatin appears at ca. –1.49V (vs. SCE) in 0.16molL^–1 Na₂B₄O₇–KH₂PO₄ (pH=7.4) supporting electrolyte containing 20% ethanol. It is ascribed to a 2e^–, 2H⁺ addition to the carbonyl group on lactone ring. If H₂O₂ is present, the reduction wave is catalyzed to produce a polarographic catalytic wave. Based on the catalytic wave, a novel method for the determination of lovastatin is proposed. A rectilinear calibration curve of the catalytic wave was obtained for lovastatin concentration in the range 1.5×10^–8 to 1.0×10^–6molL^–1. The peak current of the catalytic wave is ca. 12 times higher than that of the corresponding reduction wave. The detection limit is 8.0×10^–9molL^–1. The proposed method is simpler, faster and more sensitive than the known methods for lovastatin analysis, and can be applied to the direct determination of lovastatin in pharmaceuticals, urine and serum without preliminary separation.     

Rapid Determination of Pentazocine in Human Plasma and Urine by a Potentiometric Method

Abstract

A fast potentiometric determination method has been reported for pentazocine in human plasma without complicated pretreatments using a coated-wire potentiometric selective electrode. The sensing membrane was made by incorporating of ion-association complexes of pentazocine cation and sodium tetraphenyl borate (NaTPB) in a polyvinyl chloride. The sensor exhibited fast, stable, and linear Nernstian response over the range of 5 × 10^?5 to 0.1 mol L^?1 pentazocine with a slope of 57.8 mV per decade and with detection limit of 3.2 × 10^?5 mol L^?1. The proposed sensor has been used for determination of pentazocine in human plasma and urine.     

Voltammetric Studies of the Interaction of Tris (1,10-phenanthroline) Cobalt (III) with Bovine Serum Albumin

Recently, the studies on the interaction of DNA with small molecules have been attracting much interest1-6. These researches not only gave the important information about thermodynamics and kinetics, but also can prompt the combination between the electrode substances and biomacromolecule with super catalysis and sensor character. It is of great significance in understanding energy conversion and metabolism in live body, biomolecular structure, various physical and chemical characters for e…     

Voltammetric Study of the Hydrolysis Product of Bendiocarb at the Glassy Carbon Electrode

 Differential pulse and square wave voltammetric methods are proposed for the determination of the N-methylcarbamate insecticide Bendiocarb based on the oxidation of its hydrolysis product. A single peak (+ 0.7 V (pH 3.5)) is observed at the glassy carbon electrode. Linear relationships between the peak intensity and the concentration were obtained up to 5 μg/ml, with detection limits of 0.77 μg/ml for DPV and 0.44 μg/ml for SWV, respectively. The methods have been applied satisfactorily for the analysis of river water samples spiked with the pesticide by using the extraction with diethyl ether as preconcentration step. Concentration values as low as 0.11 μg/ml were determined with a recovery of 96 ± 3% (SWV) and 91 ± 2% (DPV). Received June 20, 2000. Revision March 6, 2001.     

Voltammetry as the First Method for Direct Determination of a Novel Antagonist of A2A Adenosine Receptors

In this article, for the first time, the analytical method for determination of a novel antagonist of A_2A adenosine receptors (8‐(4‐methoxyphenyl)‐4‐oxo‐4,6,7,8‐tetrahydroimidazo[2,1‐c][1,2,4]triazine‐3‐carbohydrazide, namely IMT), which can be used as a drug for liver diseases, was presented. For this purpose a commercially available boron‐doped diamond electrode (BDDE) in combination with differential pulse voltammetry (DPV) was applied. It was found by cyclic voltammetry (CV) that IMT displays at BDDE, as a sensor, two well‐defined oxidation peaks at potentials of 0.81 and 1.18 V and one reduction peak at 1.1 V vs. Ag/AgCl in 0.1 mol L^?1 acetate buffer (pH 4.5±0.1). The oxidation and reduction mechanism of IMT was proposed. The developed DPV method allowed the successful determination of IMT in the range of 0.05–50 μmol L^?1 with detection limit equal to 0.0094 μmol L^?1 and without any chemical modifications and electrochemical pretreatment of the electrode surface. The proposed procedure allows the determination of IMT in vitro directly from urine samples.     

Electrochemical Behaviors of Baicalin at an Electrochemically Activated Glassy Carbon Electrode and Its Determination in Human Blood Serum

Electrochemical behavior of baicalin (BA) at an electrochemically activated glassy carbon electrode (GCE) had been investigated in Britton‐Robinson (B‐R) buffer solution (pH = 2.87) by cyclic voltammetry (CV) and square wave voltammetry (SWV). The experimental results suggested that the electrode exhibited an electrocatalytic activity toward the redox of BA. The electron transfer coefficient (α) and the standard rate constant (k_s) of BA at the electrochemically activated glassy carbon electrode were calculated. The reaction mechanism was proposed and discussed in this work. Under the selected conditions, the reduction peak current was linearly dependent on the concentration of BA in the range of 5.0 × 10^?8 to 3.0 × 10^?6 mol L^?1 (r = 0.9990), with a detection limit of 2.0 × 10^?8 mol L^?1. The relative standard deviation (R.S.D.) for five times successful determination of 1.0 × 10^?6 mol L^?1 baicalin were 2.9%. The proposed method was also successfully applied for the determination of BA in human blood serum.     

Anodic Polarographic Determination of Nilvadipine in Dosage Forms and Spiked Human Urine

 The anodic polarographic behaviour of nilvadipine was studied by using direct-current (DC), polarography and differential-pulse polarography (DPP). Nilvadipine, being a dihydropyridine derivative, exhibits well-defined anodic waves over the whole pH range of the Britton-Robinson buffers (BRb). In BRb of pH = 4, the diffusion-current constant was 6.45 ± 0.07 μA · mM⁻¹. The current-concentration plots are rectilinear over the ranges 1.6–12.8 and 0.2–12.8 μg/ml for DC polarography and DPP, respectively, with minimum detectability of 0.05 μg/ml (1.3 × 10⁻⁷ M) in case of the latter technique. The proposed method was successfully applied for determination of the drug in commercial capsules containing the drug, the percentage recoveries being in good agreement with the label claim. Furthermore, the method was applied for the determination of the drug in spiked human urine, the percentage recovery being 96.84 ± 2.83. Received January 25, 2001 Revision June 18, 2001     

Voltammetric Studies of Propylthiouracil at a Carbon-Paste Electrode Modified with Cobalt(II)-4-chlorosalophen: Application to Voltammetric Determination in Pharmaceutical and Clinical Preparations

A carbon-paste electrode chemically modified with a Schiff-base complex of cobalt (cobalt(II)-4-chlorosalophen, CoClSal) is utilized to investigate the voltammetric response of propylthiouracil (PTU). The mechanism of electrocatalytic oxidation of the compound is investigated by means of cyclic voltammetric studies applying various pHs to the buffered solutions. The modified electrode exhibits effective catalytic properties that lower the anodic overpotential and enhance the rate of electron transfer for the electrochemical oxidation of PTU. The results of the cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques showed that the modified electrode exhibits good selectivity for discriminating between the anodic wave of PTU and some biological thiols (e.g. cysteine) which may be present in human serum samples. DPV is used as a very sensitive electroanalytical method for the detection of trace amounts of PTU in pharmaceutical and clinical preparations. The results showed that the anodic peak current for the analyte in DPV varies linearly with the concentration of PTU in the range of 7.5 × 10⁻⁶ to 7.5 × 10⁻⁴ M (RSD for the slope of calibration curve <4%, n = 6).     

Simultaneous Determination of Cefepime and the Quinolones Garenoxacin, Moxifloxacin and Levofloxacin in Human Urine by HPLC-UV

A liquid chromatographic method with a C₁₈ column and acetonitrile/0.1 M phosphoric acid/ sodium hydroxide buffer (pH 3.0)/0.01 M n-octylamine (pH 3.0) as mobile phase in gradient mode has been developed and optimised for the simultaneous determination of the cephalosporin cefepime and the quinolones garenoxacin, levofloxacin and moxifloxacin. Identification and quantification was carried out with a diode-array UV detector, with working wavelengths of 256 nm for cefepime, 292 nm for levofloxacin, 294 nm for moxifloxacin and 282 nm for garenoxacin. The mobile flow-rate and sample volume injected were 1 mL min⁻¹ and 20 µL, respectively. The retention times and detection limits for each antibiotic were 4.9 min and 1.9 µg mL⁻¹ for cefepime, 7.5 min and 2.2 µg mL⁻¹ for levofloxacin, 8.9 min and 2.7 µg mL⁻¹ for moxifloxacin and 10.7 min and 1.8 µg mL⁻¹ for garenoxacin, respectively. The method was applied to the determination of the four molecules in spiked samples of human urine.     

Voltammetric Detector for Liquid Chromatography: Determination of Triclosan in Rabbit Urine and Serum

A flow-electrolytic cell containing a strand of carbon fibers has been designed and characterized for use in a voltammetric detector for high-performance liquid chromatography. The detector was used for determination of triclosan (2,4,4-trichloro-2-hydroxydiphenyl ether) in rabbit serum and urine. Analysis of rabbit serum and urine 1 day and 1 to 5 days, respectively, after ingestion of oral triclosan revealed that the concentration of triclosan was higher than for control serum and urine. The concentration reached maximum levels after 6 h and 34 h or 44 h in serum and urine, respectively. When triclosan was determined in rabbit samples with the method proposed the results obtained were comparable with those obtained by high-performance liquid chromatography with ultraviolet detection.     

Voltammetric Analysis of Naproxen in Graphite Electrodes and Its Determination in Pharmaceutical Samples

The present work discuses new findings in the electrochemistry of naproxen over graphite electrodes. This new approach, allows the proposal of a simple and competitive low‐cost method to carry out naproxen’s voltammetric quantification. Naproxen’s indirect quantification through an adsorption anodic wave was performed at a graphite bar electrode using differential pulse voltammetry. An anodic current maximum was recorded at a potential of ?0.3 V referred to a saturated Ag/AgCl reference electrode. The calibration plot having a correlation coefficient of 0.990, sensibility of 4.19±0.62 µA cm³ µg^?1, with detection and quantification limits of 0.68 and 3.3 µg cm^?3, respectively.