Voltammetric measurement of haloperidol following adsorptive accumulation at glassy-carbon electrodes

A sensitive stripping voltammetric method is reported for trace measurement of the psychotherapeutic drug haloperidol. The method is based on adsorptive preconcentration of haloperidol on the glassy-carbon electrode in an open circuit, followed by medium exchange and voltammetric determination of surface species. Cyclic voltammetry was used to explore the adsorptive behaviour and the results obtained suggest that the adsorption of haloperidol corresponds to the Frumkin-type isotherm. The adsorptive stripping response was evaluated with respect to stripping mode, electrolyte. pH, preconcentration time, concentration dependence, possible interference and other variables. The detection limit was 1.3 x 10(-9)M (10 min preconcentration) and the response was linear. The relative standard deviation (at the 1.3 x 10(-6)M level) was 2.3%. Applicability to a patient's urine sample is illustrated.     

Adsorptive stripping voltammetric determination of azithromycin at a glassy carbon electrode modified by electrochemical oxidation.

The adsorptive and electrochemical behaviors of azithromycin were investigated on a glassy carbon electrode that was electrochemically treated by anodic oxidation at +1.8 V, following potential cycling in the potential range from -0.8 to +1.0 V. The resulting electrode showed good activity to improve the electrochemical response of the drug. An adsorptive stripping voltammetric method for the determination of azithromycin at an electrochemically activated glassy carbon electrode has been developed. Azithromycin was accumulated in phosphate buffer, pH 6, at a potential of +0.3 V (vs. Ag/AgCl electrode) for a certain time, and then determined by differential pulse voltammetry. The oxidative peak current at +0.82 V, at a scan rate of 20 mV s(-1), was a linear function of the concentration in the ranges of 0.25 - 2 microg mL(-1) and 1 - 10 microg mL(-1) using a 240 or 60 s(-1) preconcentration time, respectively. Application of the method to the determination of azithromycin in pharmaceuticals resulted in an acceptable deviation from the stated concentration. The preconcentration medium-exchange approach was utilized for the selective determination of the drug in spiked urine samples with satisfactory results. The peak current was linear with the drug concentration in the range of 0.5 - 3.5 microg per mL urine. The detection limit was 0.2 microg mL(-1) urine. The recovery levels of the method reached 96.3%.     

A Sensitive Voltammetric Method for the Determination of Diazinon Insecticide

A sensitive voltammetric method is developed for the determination of diazinon, an organophosphorus pesticide, using a Nafion®-coated glassy carbon electrode as an enrichment film. The analysis of diazinon in aqueous solutions using sensitive instrumental methods has gained importance. Investigation of the electrochemical behavior of diazinon on a Nafion®-coated glassy carbon electrode reveals the presence of a specific oxidation peak of analytical significance. The experimental parameters, such as pH, film thickness, preconcentration potential, preconcentration time, and square-wave voltammetric parameters were optimized. Using this method, a linear calibration curve for diazinon was obtained up to 5 M range in pH 1 citrate buffer solution with a detection limit (S/N = 3) of 75 nM.     

Voltammetric determination of methidathion insecticide

An electroanalytical method has been developed for the determination of methidathion by squarewave voltammetry on a Nafion®-coated glassy carbon electrode in aqueous solutions with 0.05 M acetate buffer as a supporting electrolyte. The best voltammetric conditions were found to be pH 4.0, a preconcentration potential of 0.45 V, and a preconcentration time of 60 s. The experimental parameters, such as pH, film thickness, preconcentration potential, preconcentration time, and square-wave voltammetric parameters, were optimized. Using this method, the calibration curve is linear in the range 5 × 10^?8?7 × 10^?7 M with a detection limit (S/N = 3) of 30 nM.     

Rapid preconcentration method for the determination of pyrethroid insecticides in vegetable oils and butter fat and simultaneous determination by gas chromatography-electron capture detection and gas chromatography-mass spectrometry

A simple and rapid solid-phase extraction (SPE)-GC method for the preconcentration and quantification of pyrethroids at low nanogram levels in oils and high fat content samples is presented. The method was studied using seven highly persistent pyrethroid insecticides, viz., cypermethrin, deltamethrin, fenvalerate, cyfluthrin, allethrin, cyhalothrin and permethrin. Preconcentration was achieved by treating the oil samples with methyltrioctylammonium chloride and subsequent elution of the pyrethroid molecules from a graphitized carbon black SPE cartridge using 5 ml of acetonitrile. Pyrethroid quantification was achieved by GC with electron capture detection. Recoveries of the pyrethroids at fortification levels of 0.05-0.5 ppm were 94-105%. Storage on graphitized carbon black for 30 d lowered the recovery of the pyrethroids by only 3-6%. The method compared well with results obtained by a GC-MS method. The relative standard deviation at a concentration level of 0.05-0.2 microgram ml-1 ranged from 1.31 to 5.16%. The limit of detection achieved was 0.002 microgram ml-1 without any additional clean-up and with little interference from lipids during analysis.     

Simultaneous detection of cadmium, copper, and lead using a carbon paste electrode modified with carbamoylphosphonic acid self-assembled monolayer on mesoporous silica (SAMMS)

A new sensor was developed for simultaneous detection of cadmium (Cd²⁺), copper (Cu²⁺), and lead (Pb²⁺), based on the voltammetric response at a carbon paste electrode modified with carbamoylphosphonic acid (acetamide phosphonic acid) self-assembled monolayer (SAM) on mesoporous silica (Ac-Phos SAMMS). The adsorptive stripping voltammetry (AdSV) technique involves preconcentration of the metal ions onto Ac-Phos SAMMS under an open circuit, then electrolysis of the preconcentrated species, followed by a square wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated. The voltammetric responses increased linearly with the preconcentration time from 1 to 30 min or with metal ion concentrations ranging from 10 to 200 ppb. The responses also evolved in the same fashion as adsorption isotherm in the pH range of 2-6. The metal detection limits were 10 ppb after 2 min preconcentration and improved to 0.5 ppb after 20 min preconcentration.     

Adsorptive Stripping Voltammetric Measurements of Trace Molybdenum at the Bismuth Film Electrode

Bismuth‐film electrodes on glassy‐carbon substrates have been successfully applied for adsorptive‐stripping voltammetric measurements of trace molybdenum in the presence of chloranilic acid (CAA). The procedure is based on the preconcentration of the molybdenum‐chloranilic acid complex at a preplated bismuth film electrode held at ?0.55 V (vs. Ag/AgCl), followed by a negatively‐sweeping square‐wave voltammetric scan. Factors influencing the adsorptive stripping performance, including different ligands, solution pH, CAA concentration, preconcentration time and potential, have been optimized. The response compares favorably with that observed at mercury film electrodes, and is linear over the 5–50 μg/L Mo concentration range (one min preconcentration). A detection limit of 0.2 μg/L molybdenum is obtained following a 10 min accumulation. High stability is indicated from the reproducible response of a 100 μg/L molybdenum solution (n= 60; RSD=2.6%). Applicability to seawater samples is demonstrated.     

Trace measurements of colchicine by adsorptive stripping voltammetry

A highly sensitive voltammetric method for trace measurements of the alkaloid colchicine is described. The method is based on the controlled adsorptive accumulation of the drug at the hanging mercury drop electrode, followed by voltammetric determination of the surface species. The adsorptive stripping response is evaluated with respect to preconcentration time and potential, solution pH, voltammetric waveform and other variables. With a 10-min preconcentration, a detection limit of 1.3 x 10(-10)M is obtained. The relative standard deviation (at the 1 x 10(-7)M level) is 1.1%. Applicability to urine analysis is illustrated.     

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.     

Electrochemical and Spectroscopic Studies on the Interaction of Gatifloxacin,Moxifloxacin and Sparfloxacin with DNA and Their Analytical Applications

The electrochemical oxidation of the three fluoroquinolone drugs FQs: gatifloxacin GTF, moxifloxacin MXF and sparfloxacin SPF, at the bare and DNA‐modified glassy carbon electrodes has been studied by voltammetric techniques. The three FQs showed one irreversible oxidation peak at potential range 0.85–0.91 V vs. Ag‐AgCl, in phosphate buffer of pH 7.0. Differential pulse voltammetry (DPV) and UV‐absorption spectroscopic techniques were employed to probe the interaction between the FQs and calf thymus double stranded deoxyribonucleic acid (ds CT‐DNA). From electrochemical data, the binding constant between DNA and the gatifloxacin, moxifloxacin and sparfloxacin are calculated to be 3228, 2596 and 2857 M^?1 respectively. Based on electrochemical and spectroscopic results, the mode of binding of fluoroquinolone to DNA through combined effect of intercalation and electrostatic interaction was concluded. A detection scheme based on a preconcentration and differential pulse voltammetric (DPV) determination at dsDNA modified glassy carbon electrode (DNA/GCE) was proposed for the trace determination of the studied analytes. The developed method was successfully applied to the determination of the FQs in pharmaceutical formulations.     

Electrochemical determination of meloxicam in pharmaceutical preparation and biological fluids using oxidized glassy carbon electrodes

The adsorptive and electrochemical behaviors of meloxicam (MLC) was investigated on a glassy carbon electrode that was electrochemically treated by anodic oxidation at +1.8 V, following potential cycling in the potential range from -0.8 to 1.0 V vs. Ag/AgCl reference electrode. The resulting electrode showed a good activity to improve the electrochemical response of the drug. MLC was accumulated at an electrochemically activated glassy carbon electrode (phosphate buffer pH 6) in a certain time and then determined by linear sweep voltammetry. The oxidative peak currents showed a linear function in the concentration ranges of 0.02 to 10 microM using a 240 s preconcentration time. The preconcentration medium-exchange approach was utilized for the selective determination of the drug in spiked urine and plasma samples with satisfactory results. The recovery values of the proposed method obtained 105% (RSD 2.5%) and 100% (RSD 1.8%) for urine and plasma samples, respectively. Also, the proposed method has been successfully used for determination of MLC in tablets.     

Selective Determination of Vitamin B2 at Electrochemically Activated Glassy Carbon Electrode

Electrochemically activated glassy carbon electrodes were applied to the preconcentration and electroanalysis of Vitamin B₂ (VB₂) in multivitamin preparation. Voltammetric peak currents showed linear response for VB₂ concentrations in the range between 0.1 to 3.0 M with a large slope of 12.2 AM^-1 and a correlation coefficient of 0.996. The reproducibility of the voltammetric measurements was usually less than 7% RSD for five replicate measurements. Common vitamin and metal species did not interfere the determination.     

Platinum Nanoparticles Decorated Multiwalled Carbon Nanotubes – Ionic Liquid Composite Film Coated Glassy Carbon Electrodes for Sensitive Determination of Theophylline

Platinum nanoparticles (Pt_nano) decorated multiwalled carbon nanotubes (MWCNTs)–1‐octyl‐3‐methylimidazolium hexafluorophosphate ([omim][PF₆]) composite material (MWCNTs‐Pt_nano‐[omim][PF₆]) was fabricated and characterized for the first time. In the presence of [omim][PF₆], more Pt_nano could deposit on MWCNTs. The average diameter of the deposited Pt_nano was about 5 nm. The composite material film coated glassy carbon electrode (GCE) exhibited sensitive voltammetric response to theophylline (TP). Under the optimized conditions (i.e., preconcentration for 2 minutes on open circuit in 0.10 M pH 3.0 phosphate buffer), the anodic peak current of TP at about 1.1 V (vs. SCE) was linear to TP concentration over the range of 1.0×10^?8–1.0×10^?5 M. The detection limit was estimated to be 8.0×10^?9 M. The modified electrode was successfully applied to the determination of TP in medicine tablet and green tea. In addition, the voltammetric responses of hypoxanthine (HX), xanthine (Xan) and uric acid (UA) on the MWCNTs‐Pt_nano‐[omim][PF₆]/GCE were also discussed.     

Square wave anodic stripping voltammetric determination of lead(II) using a glassy carbon electrode modified with a lead ionophore and multiwalled carbon nanotubes

We report on a glassy carbon electrode (GCE) modified with a lead ionophore and multiwalled carbon nanotubes. It can be applied to square wave anodic stripping voltammetric determination of Pb(II) ion after preconcentration of Pb(II) at ?1.0?V (vs. SCE) for 300?s in pH?4.5 acetate buffer containing 400?μg?L^?1 of Bi(III). The ionophore-MWCNTs film on the GCE possesses strong and highly selective affinity for Pb(II) as confirmed by quartz crystal microbalance experiments. Under the optimum conditions, a linear response was observed for Pb(II) ion in the range from 0.3 to 50?μg?L^?1. The limit of detection (at S/N?=?3) is 0.1?μg?L^?1. The method was applied to the determination of Pb(II) in water samples with acceptable recovery.

电位溶出分析法的理论和验证

本文推导了电位溶出分析法的过渡时间和电位-时间曲线方程式,并成功地进行了验证,理论和实验结果十分符合。     

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   

Trace measurements of the antineoplastic agent methotrexate by adsorptive stripping voltammetry

An extremely sensitive voltammetric method is presented for trace measurement of the cancer chemotherapy drug methotrexate. The method is based on controlled adsorptive preconcentration of methotrexate on the hanging mercury-drop electrode, followed by voltammetric determination of the surface species. Cyclic voltammetry was used to explore the interfacial behaviour. The adsorptive stripping response was evaluated with respect to preconcentration time and potential, pH, concentration dependence, stripping mode, possible interferences, and other variables. The detection limit found was 2 x 10(-9)M (5-min preconcentration), the response was linear, and the relative standard deviation (at the 1.6 x 10(-7)M level) 2.2%. Sensitive adsorptive stripping measurements were also obtained by use of a carbon-paste disk electrode. Applicability to urine analysis is illustrated.     

Determination of chlorprothixene and its sulfoxide metabolite in plasma by high-performance liquid chromatography with ultraviolet and amperometric detection

This communication describes a rapid, sensitive and selective method for the assay of chlorprothixene and its sulfoxide metabolite in human plasma, using reversed-phase high-performance liquid chromatography. Alkalinized plasma was extracted with heptane--isoamyl alcohol (99:1), after addition of thioridazine as the internal standard. The residue obtained after evaporation of this extract was chromatographed on a cyano column, using acetonitrile--0.02 M potassium dihydrogen phosphate pH 4.5 (60:40) as the mobile phase with ultraviolet (229 nm) detection. Quantitation was based on peak height ratios over the concentration range of 5.0-50.0 ng/ml for both compounds with 85% and 90% recovery for chlorprothixene and its sulfoxide metabolite, respectively, using a 1.0-ml plasma sample. The assay chromatographically resolves chlorprothixene and the sulfoxide metabolite from the N-desmethyl metabolite, which can only be semi-quantitated owing to low and variable recoveries. The method was used to obtain plasma concentration versus time profiles in two subjects after oral administration of 100 mg of chlorprothixene suspension and in two additional subjects following overdosages of chlorprothixene estimated to exceed several hundred milligrams. These analyses demonstrated that the sulfoxide metabolite is the predominant plasma component following therapeutic administration and overdosages. High-performance liquid chromatography with oxidative amperometric detection with the glassy carbon electrode was also evaluated. Although this procedure demonstrated comparable sensitivity and precision to ultraviolet detection for the analysis of chlorprothixene and N-desmethyl chlorprothixene, the sulfoxide metabolite could not be measured with high sensitivity (less than 100 ng/ml) owing to endogenous interferences. Hence the utility of this alternative assay technique is limited.     

Quantification of Quercetin Using Glassy Carbon Electrodes Modified with Multiwalled Carbon Nanotubes Dispersed in Polyethylenimine and Polyacrylic Acid

This work reports the highly sensitive detection of quercetin using glassy carbon electrodes modified with multiwall carbon nanotubes (MWCNT) dispersed in polyethylenimine and poly(acrylic acid). The adsorptive stripping with square wave voltammetric transduction allowed the detection of 7.5 nM quercetin after 1.0 min accumulation at open circuit potential. The amperometric detection at 0.150 V is reported as an easier and simpler alternative to determine quercetin, with detection limits of 0.2 µM. The careful selection of the working conditions also made possible the detection of submicromolar levels of quercetin in the presence of excess of rutin. The proposed methodology was successfully used to quantify quercetin in onion samples.     

Determination of hydralazine and metabolites in urine by liquid chromatography with electrochemical detection

The cyclic voltammetric behavior of hydralazine and its primary metabolites, the pyruvate and acetone hydrazones, was examined in the positive potential range at both conventional and electrochemically pretreated glassy carbon electrodes. The enhanced oxidations observed at the treated surface were used as the basis of amperometric electrochemical detection of the compounds following reversed-phase liquid chromatography. The detection limits so obtained at +0.75 V vs. Ag/AgCl (1, 3, and 5 ng injected, respectively) were comparable to those previously reported for absorption and fluorescence detection approaches employing derivatization/preconcentration procedures. For liquid chromatography with electrochemical detection, however, direct quantitation of all three species in urine samples was readily accomplished without any chemical derivatization or sample treatment operations other than particulate filtration.