Electrochemical study of zolpidem at glassy carbon electrode and its determination in a tablet dosage form by differential pulse voltammetry

The oxidative behaviour of, a hypnotic drug, zolpidem was studied at glassy carbon electrode in Britton-Robinson buffer over the pH range 2.0-11.0 using cyclic, linear sweep and differential pulse voltammetry. Oxidation of the drug was effected in a single irreversible, diffusion-controlled step. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 8.0 at +0.889 V (vs. Ag/AgCl) on glassy carbon electrode. This process could be used to determine zolpidem concentrations in the range 5.0 x 10(-7) M to 1.0 x 10(-5) M with a detection limit of 2.0 x 10(-7) M. The method was applied, without any interference from the excipients, to the determination of the drug in a tablet dosage form.     

Determination of EDTA species in water by second-derivative square-wave voltammetry using a chitosan-coated glassy carbon electrode.

Based on the adsorption of Fe(EDTA)- on a chitosan-coated glassy carbon electrode, a second-derivative square-wave voltammetry for the determination of the EDTA species in water samples was investigated. The measuring range of EDTA was from 6.0 x 10(-7) to 5.0 x 10(-5) mol/L with a correlation coefficient of 0.998 and a detection limit of 2.8 x 10(-7) mol/L. The relative standard deviation was less than 6.2% (n = 5) and the recovery was in the range of 98-105% for the determination of practical samples. The result was consistent with that from the HPLC method.     

Enhanced electrochemical detection of ketorolac tromethamine at polypyrrole modified glassy carbon electrode.

A glassy carbon electrode modified with a coating of polypyrrole (Ppy) exhibited an attractive performance for the detection and determination of a non-steroidal and non-narcotic analgesic compound, ketorolac tromethamine (KT). Cyclic voltammetry, differential pulse and square wave voltammetry were used in a combined way to identify the electrochemical characteristics and to optimize the conditions for detection. For calibrating and estimating KT, square-wave voltammetry was mainly used. The drug shows a well-defined peak at -1.40 V vs. Ag/AgCl in the acetate buffer (pH 5.5). The existence of Ppy on the surface of the electrode gives higher electrochemical active sites at the electrode for the detection of KT and preconcentrate KT by adsorption. The square-wave stripping voltammetric response depends on the excitation signal and the accumulation time. The calibration curve is linear in the range 1 x 10(-11) to 1 x 10(-7) M with a detection limit of 1.0 x 10(-12) M. Applicability to serum samples was also demonstrated. A detection limit of 1.0 ng ml for serum was observed. Square-wave voltammetry shows superior performance over UV spectroscopy and other techniques.     

Voltammetric determination of niclosamide at a glassy carbon electrode

A very sensitive and selective procedure was developed for the determination of niclosamide based on square-wave voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate the electrochemical reduction of niclosamide at a glassy carbon electrode. Niclosamide was first irreversibly reduced from NO2 to NHOH at -0.659 V in aqueous buffer solution of pH 8.5. Reversible and well defined peaks at -0.164 V and -0.195 V (vs. Ag/AgCl) were obtained that are responsible for two electron peaks between NHOH and NO. Following optimisation of the voltammetric parameters, pH and reproducibility, a linear calibration curve over the range 5 x 10(-8)-1 x 10(-6) mol dm(-3) was achieved. The detection limit was found to be 2.05 x 10(-8) mol dm(-3) niclosamide. For eight successive determinations of 5 x 10(-7) mol dm(-3) niclosamide, a relative standard deviation of 2.4% was obtained. This voltammetric method was applied to the direct determination of niclosamide in tablets. The results of the analysis suggest that the proposed method has promise for the routine determination of niclosamide in the products examined.     

Electrochemical study of fluvastatin sodium – analytical application to pharmaceutical dosage forms, human serum, and simulated gastric juice

The oxidation of fluvastatin sodium on a glassy carbon electrode has been studied by use of a variety of voltammetric techniques. Different conditions were investigated to optimize the determination of fluvastatin sodium. The dependence of the intensities of currents and potentials on pH, concentration, scan rate, and nature of the buffer was investigated. Oxidation of fluvastatin sodium was found to be diffusion-controlled and irreversible. The best results for the determination of fluvastatin sodium were obtained by using differential pulse and square-wave voltammetric techniques in Britton-Robinson buffer at pH 10.04. Differential pulse and square-wave voltammetry at a glassy carbon electrode resulted in linear calibration in the range 8x10(-6) to 6x10(-4) mol L(-1) and detection limits of 1.07x10(-6) and 7.99x10(-7) mol L(-1), respectively. The proposed methods were successfully applied to the determination of the drug in capsules and biological fluids. Excipients did not interfere with the determination. Statistical validation revealed that the methods were free from significant systematic errors.     

Voltammetric detection of sulfonamides at a poly(3-methylthiophene) electrode

Detection of sulfonamide compounds in a mixture of standards at a poly(3-methylthiophene) coated on glassy carbon (GC) electrode is reported. The polymer, poly(3-methylthiophene), was electrochemically synthesized at a GC rotating disk-working electrode versus Ag/AgCl using cyclic voltammetry (+0.5 to +2.0 V). Square wave voltammetry (SQWV) with cathodic reduction (0 to -4.0 V) was used for the detection of seven sulfonamide compounds in a mixture. The working concentration ranges (curvilinear) established for different compounds in Britton-Robinson (BR) buffer (pH 6.26), were: 5.0x10(-6)-3.2x10(-3) M sulfamerazine, 5.0x10(-6)-3.2x10(-3) M sulfadiazine, 7.5x10(-7)-3.2x10(-4) M sulfasalazine, 9.0x10(-7)-5.0x10(-4) M sulfamethazine, 6.5x10(-8)-3.5.0x10(-5) M sulfamethoxazole, 9.7x10(-8)-5.0x10(-5) M sulfathiazole, and 9.0x10(-8)-3.2x10(-5) M 5-sulfaminouracil. Detection limits were calculated as: 3.9x10(-6) M for sulfamerazine; 4.0x10(-6) M sulfadiazine; 2.5x10(-7) M sulfasalazine; 3.7x10(-7) M sulfamethazine; 4.0x10(-8) M sulfamethoxazole; 6.4x10(-8) M sulfathiazole and 6.0x10(-9) M 5-sulfaminouracil. The data suggests a potential application of the poly(3-methylthiophene) (P3MT) electrode for determination of sulfonamides in veterinary and other applications.     

Differential pulse anodic stripping voltammetric determination of traces of copper with a tobramycin-Nafion modified electrode.

A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results.     

Voltammetric determination of sinomenine in biological fluid using a glassy carbon electrode modified by a composite film of polycysteic acid and carbon nanotubes

Polycysteic acid based electrochemical oxidation of L-cysteine (CySH) and carbon nanotubes (CNTs) formed a composite thin film material at a glassy carbon electrode (GCE) that was used a novel modifier for electroanalytical determination of sinomenine which is used for rheumatoid arthritis treatment. The determination of sinomenine at the composite modified electrode was studied by differential pulse voltammetry (DPV). The peak current obtained at + 0.632 V (vs SCE) from DPV was linearly dependent on the sinomenine concentration in the range of 1.0 x 10(-7) to 6.0 x 10(-5) M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0 x 10(-8) M. The electrochemical reaction mechanism of sinomenine was also discussed. This new method was then applied to the high-throughput determination of sinomenine in human serum samples with satisfactory results. This polycysteic acid/CNTs composite film may be considered to be a promising, low-cost, durable, and biocompatible material for the modification of sensors in applications to pharmaceutical and biomedical analysis.     

Quantification of terbutaline in pharmaceutical formulation and human serum by adsorptive stripping voltammetry at a glassy carbon electrode

The electrochemical oxidative behavior of terbutaline at the glassy carbon electrode was studied in a series of the Britton-Robinson buffer of pH 2--11. Cyclic and square-wave voltammograms of terbutaline at the pH values 相似文献   

Poly(amidosulfonic acid) modified glassy carbon electrode for determination of isoniazid in pharmaceuticals

Amidosulfonic acid was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the chemically modified electrode, which showed high stability, good selectivity and reproducibility for determination of isoniazid. The modified electrode showed an excellent electrocatalytical effect on the oxidation of isoniazid. Under the optimum conditions, there was a good linear relationship between anodic peak current and isoniazid concentration in the range of 5.0 x 10(-8)- 1.0 x 10(-5) M, and a detection limit of 1.0 x 10(-8) M (S/N = 3) was obtained after 120 s at the accumulation potential of - 0.2 V (vs. SCE). This developed method had been applied to the direct determination of isoniazid in injection and tablet samples with satisfactory results.     

Electrochemical oxidation of luteolin at a glassy carbon electrode and its application in pharmaceutical analysis

Luteolin is a flavonoid reported to occur widely in many medicinal plants. The electrochemical behavior of luteolin was studied in phosphate buffer solution (PBS) of pH 4.0 at a glassy carbon electrode (GCE) by cyclic voltammetry (CV) and differential pulse voltammetric method (DPV). The results indicated the well-defined redox peak of luteolin which was involving two electrons and two protons was observed and the electrode process is adsorption-controlled. The charge transfer coefficient (alpha) was calculated as 0.66. The relationships between oxidation peak current and the concentration of luteolin are linear in the range of 1.0 x 10(-8) - 1.0 x 10(-6) M by DPV method. The detection limit had been estimated as 5.0 x 10(-9) M. The facile and rapid method has been successfully applied to the detection of luteolin in tablets.     

Voltammetric determination of terbinafine in biological fluid at glassy carbon electrode modified by cysteic acid/carbon nanotubes composite film

The electrochemical oxidation of L-cysteine (CySH) in presence of carbon nanotubes (CNTs) formed a composite film at a glassy carbon electrode (GCE) as a novel modifier for directly electroanalytical determination of terbinafine without sample pretreatment in biological fluid. The determination of terbinafine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.156 V (vs. SCE) from DPV was linearly dependent on the terbinafine concentration in the range of 8.0 x 10(-8)-5.0 x 10(-5 )M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N=3) was 2.5 x 10(-8 )M. The low-cost modified electrode showed good sensitivity, selectivity, and stability. This developed method had been applied to the direct determination of terbinafine in human serum samples with satisfactory results. It is hopeful that the modified electrode will be applied for the medically clinical test and the pharmacokinetics in future.     

Electrochemical adsorptive behavior of some fluoroquinolones at carbon paste electrode.

Cyclic voltammetry and differential pulse voltammetry were used to explore the adsorption behavior of three antibacterial agents at a carbon paste electrode. The drugs were accumulated on a carbon paste electrode, and a well-defined oxidation peak was obtained in acetate buffer (pH 5.0). The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH and accumulation time. A simple, precise, inexpensive and sensitive voltammetric method has been developed for the determination of the cited drugs (Lomefloxacin (LFX), Sparfloxacin hydrochloride (SFX), and Gatifloxacin (GFX)). A linear calibration was obtained from 2 x 10(-7) M to 4 x 10(-5) M for LFX, 2 x 10(-7) M to 6 x 10(-5) M for SFX, and GFX. The limits of detection (LOD) were 4.2 x 10(-7), 7 x 10(-7) and 6.6 x 10(-7) M, while the limits of quantification (LOQ) were 1.4 x 10(-6), 2.3 x 10(-6) and 2.2 x 10(-6) M for LFX, SFX, and GFX, respectively. The R. S. D. of five measurements at the 1 x 10(-6) M level were 0.4, 0.5 and 0.3 for LFX, SFX and GFX, respectively. The method was applied to the determination of LFX, SFX and GFX in dilute urine samples and dosage forms, and compared with the HPLC method.     

Determination of ketorolac in human serum by square wave adsorptive stripping voltammetry

The adsorption behavior of ketorolac on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The square wave voltammetric response of ketorolac depends on the parameters of the square wave voltammetry excitation signal as well as on the pH of the medium and the accumulation time. The drug was accumulated at HMDE and a well-defined peak was obtained at -1.41 V versus. Ag/AgCl (saturated KCl) in acetate buffer of pH 5.0. A square-wave adsorptive stripping voltammetric method for the quantitative determination of ketorolac was developed. The linear concentration range was 1x10(-10)-1x10(-8) when using 300 s accumulation at -0.8 V. The detection limit of ketorolac was 1.0x10 (-11)M . The precision was excellent with relative standard deviation of 3.85% at concentration of 5x10 (-8)M after 60 s accumulation time. Applicability to serum samples was illustrated. A detection limit of 14 ng per ml of serum was obtained.     

A poly(3-acetylthiophene) modified glassy carbon electrode for selective voltammetric measurement of uric acid in urine sample

A reliable and reproducible method for the determination of uric acid in urine samples has been developed. The method is based on the modification of a glassy carbon electrode by 3-acetylthiophene using cyclic voltammetry. The poly(3-acetylthiophene) modified glassy carbon electrode showed an excellent electrocatalytic effect towards the oxidation of uric acid in 0.1 m phosphate buffer solution (PBS) at pH 7.2. Compared with a bare glassy carbon electrode (GCE), an obvious shift of the oxidation peak potential in the cathodic direction and a marked enhancement of the anodic current response for uric acid were observed. The poly(3-acetylthiophene)/GCE was used for the determination of uric acid using square wave voltammetry. The peak current increased linearly with the concentration of uric acid in the range of 1.25 x 10(-5)-1.75 x 10(-4) M. The detection limit was 5.27 x 10(-7) M by square wave voltammetry. The poly(3-acetylthiophene)/GCE was also effective to determine uric acid and ascorbic acid in a mixture and resolved the overlapping anodic peaks of these two species into two well-defined voltammetric peaks in cyclic voltammetry at 0.030 V and 0.320 V (vs. Ag/AgCl) for ascorbic acid and uric acid, respectively. The modified electrode exhibited stable and sensitive current responses toward uric acid and ascorbic acid. The method has successfully been applied for determination of uric acid in urine samples.     

Investigation of electrochemical behavior of lipid lowering agent atorvastatin calcium in aqueous media and its determination from pharmaceutical dosage forms and biological fluids using boron-doped diamond and glassy carbon electrodes

The electrochemical behavior of atorvastatin calcium at glassy carbon and boron-doped diamond electrodes has been studied using voltammetric techniques. The possible mechanism of oxidation was discussed with model compounds. The dependence of the peak current and potentials on pH, concentration, scan rate and nature of the buffer were investigated for both electrodes. The oxidation of atorvastatin was irreversible and exhibited a diffusion-controlled fashion on the diamond electrode. A linear response was obtained within the range of 9.65 x 10(-7) - 3.86 x 10(-5) M in 0.1 M H(2)SO(4) solution for both electrodes. The detection limits of a standard solution are estimated to be 2.11 x 10(-7) M with differential pulse voltammetry (DPV) and 2.05 x 10(-7)M with square wave voltammetry (SWV) for glassy carbon electrode, and 2.27 x 10(-7) M with DPV and 1.31 x 10(-7)M with SWV for diamond electrodes in 0.1 M H(2)SO(4) solution. The repeatability of the methods was found good for both electrodes. The methods were fully validated and successfully applied to the high-throughput determination of the drug in tablets, human serum and human urine with good recoveries.     

Electropolymerization of negatively charged Ni(II) complex for the selective determination of dopamine in the presence of ascorbic acid

Electrodes for the dopamine (DA) determination in biological samples have been developed with improved selectivity and sensitivity in an excess of ascorbic acid (AA). Negatively charged Ni(II) complex was synthesized and electropolymerized on the glassy carbon electrode to impart the surface with anionic characteristics that could act both as a catalyst and as a discriminating layer against AA based on the electrostatic interaction. Thus prepared electrodes enabled selective determination of DA even in a large excess of AA by differential pulse voltammetry at physiological pH. Linear response was found down to 1.0 x 10(-7) M with 5.0 x 10(-9) M of LOD (Limit of Detection). In a flow injection analysis performed in an amperometric mode, the detection limit was lowered by two orders of magnitude down to 1.0 x 10(-9) M with a linear range of 1.0 x 10(-9) to 1.0 x 10(-6) M. The relative standard deviation was found to be 3.36% from 25 independent measurements for 1.0 x 10(-5) M of DA. Stable oxidation current of DA was observed even after 30 days storage in air. The recoveries of DA in the 100-fold diluted human urine samples were 97.7% for 4 measurements. The rate constant for the DA oxidation was 1.3 x 10(-3) cm s(-1) from hydrodynamic experiments using a rotating disk electrode.     

Electrocatalytic determination of ascorbic acid on a glassy carbon electrode chemically modified with cobalt pentacyanonitrosylferrate.

An electrochemically prepared thin film of cobalt pentacyanonitrosylferrate (GC/CoPCNF) was used as a surface modifier for glassy carbon electrodes. The oxidation of ascorbic acid on a glassy carbon electrode modified with GC/CoPCNF as a working electrode was studied using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry in a 0.25 M KNO3 + 0.25 M phosphate buffer (pH 7) solution. The glassy carbon modified with CoPCNF showed good electrocatalytic activity toward ascorbic acid oxidation. The kinetics of the catalytic reaction was investigated, and the average value of the rate constant (k) for the catalytic reaction and the diffusion coefficient (D) were evaluated by different approaches for ascorbic acid, and were found to be 3.3 +/- 0.3 x 10(2) M(-1) s(-1) and 3.2 +/- 0.3 x 10(-6) cm2 s(-1), respectively.     

Anodic oxidation of etodolac and its square wave and differential pulse voltammetric determination in pharmaceuticals and human serum

A voltammetric study of the oxidation of etodolac has been carried out at the glassy carbon electrode. The electrochemical oxidation of etodolac was investigated by cyclic, linear sweep, differential pulse and square wave voltammetry using glassy carbon electrode. Different parameters were tested to optimize the conditions for the determination of etodolac. The dependence of intensities of currents and potentials on pH, concentration, scan rate, nature of the buffer was investigated. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in Britton-Robinson buffer at pH 2.15 for differential pulse and square wave voltammetric techniques. The linear response was obtained in the ranges of 2.10(-6)-8.10(-5) M with a detection limit of 6.8x10(-7) and 6x10(-6)-8x10(-5) M with a detection limit of 1.1x10(-6) M for differential pulse and square wave voltammetric techniques, respectively. Based on this study, simple, rapid, selective and sensitive two voltammetric methods were developed for the determination of the etodolac in tablet dosage form and human serum.     

Determination of trace amounts of dipyridamole by stripping voltammetry using a Nafion modified electrode

This paper presents a new method for determination of dipyridamole by anodic stripping voltammetry using a Nafion modified glassy carbon electrode. The stripping peak current was proportional to the concentration of dipyridamole over the range of 1.0 x 10(-9)-8.0 x 10(-8) M in (pH 1.7) BrittondashRobinson buffer with 1 min accumulation. The detection limit has been estimated as 8.0 x 10(-11) M with 4 min accumulation. The method has been successfully applied to the determination of dipyridamole in human serum.