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At least 145 records · Page 8Linked to original sources
PubMed2002

Determination of nitrofurantoin drug in pharmaceutical formulation and biological fluids by square-wave cathodic adsorptive stripping voltammetry.

Nitrofurnation is an antibacterial drug. It is used in the treatment of initial or recurrent urinary tract infections caused by susceptible organisms. The cyclic voltammogram of the drug in Britton-Robinson buffers (pH 2-11) exhibited a single well-defined cathodic peak at the hanging mercury drop electrode, that due to the reduction of its nitro group to the amine stage. A fully validated, sensitive, and reproducible developed procedure was described for determination of the drug in bulk form, pharmaceutical formulation, human serum and human urine using, square-wave cathodic adsorptive stripping voltammetry. The optimal experimental parameters for the drug assay were: accumulation potential = -0.4 V (vs. Ag/AgCl/ KCl(s)), accumulation time = 40 s, frequency = 120 Hz, pulse amplitude = 50 mV and scan increment = 10 mV in Britton-Robinson buffer (pH 10). A mean percentage recovery of 100.68 +/- 0.17 (n = 5) and a detection limit of 1.32 x 10(-10) M of bulk drug were achieved. Applicability to assay of the drug in pharmaceutical formulation, human serum and human urine was studied and illustrated. The mean percentage recoveries were found as: 101.49 +/- 0.65, 103.94 +/- 0.73 and 101.98 +/- 0.52 (n = 5) in pharmaceutical formulation, human serum and human urine, respectively. Detection limits of 2.86 x 10(-10) M and 5.77 x 10(-10) M nitrofurantoin were achieved in human serum and urine, respectively.

Body Fluids↗
PubMed2003

A study of the determination of the hypertensive drug captopril by square wave cathodic adsorptive stripping voltammetry.

In this work, the determination of captopril (CPL) was studied by square wave cathodic adsorptive stripping voltammetry (SWCAdSV) on a hanging mercury drop electrode (HMDE). CPL was adsorptively preconcentrated on the mercury surface as a sparingly soluble mercury salt under stirring of the solution and then the accumulated species was reduced by a cathodic square wave voltammetric scan. The reduction current was related to the CPL concentration in the sample. The chemical and instrumental parameters affecting the response were investigated and optimized for the CPL determination. The calibration curve was linear from 0.5 to 180 microg l(-1) of CPL (depending on the preconcentration time), the limit of detection at a S/N ratio of 3 was 0.5 microg l(-1) with 300 s of preconcentration and the relative standard deviation was 3.2% at the 20 microg l(-1) level (with 120 s of preconcentration, n=8). The method was applied to the determination of CPL in two pharmaceutical formulations with recoveries of 97.9 and 98.8%. Finally, the potential for applying the proposed method to the determination of CPL in biological media is briefly discussed.

Antihypertensive Agents↗
PubMed1999

Cathodic adsorptive stripping voltammetric determination of the anti-inflammatory drug indomethacin.

Sensitive voltammetric methods have been developed for the determination of the anti-inflammatory, anti-pyretic and analgesic drug indomethacin sodium. The methods are based on the controlled adsorptive preconcentration of the drug on a hanging mercury drop electrode (HMDE), followed by tracing the voltammogram in a cathodic potential scan. The modes used are cyclic voltammetry (CV), cathodic stripping voltammetry (CSV) and differential pulse stripping voltammetry (DPSV). Amounts as low as 10 nM (10 ng x ml(-1)) (60 s preconcentration) by CSV and 0.5 microM (190 ng x ml(-1)) (300 s) by DPSV can be determined accurately. The R.S.D. at the 1 x 10(-6) M level is 1.4%. The interference of some metal ions and the application of the method to analysis of urine, plasma and pharmaceutical formulations are described.

Adolescent↗
PubMed1999

Indirect polarographic and cathodic stripping voltammetric determination of cefaclor as an alkaline degradation product.

Cefaclor is not reducible at a mercury electrode, but it can be determined polarographically and by cathodic stripping voltammetry as its initial alkaline degradation product which is obtained in high yield by hydrolysis of cefaclor in Britton-Robinson (B-R) buffer pH 10 at 50 degrees C for 30 min (reduction peak at pH 10, -0.70 V). Differential pulse polarographic calibration graphs are linear up to at least 1 x 10(-4) mol/l(-1). Recoveries of 93% of the cefaclor (n = 3) were obtained from urine spiked with 38.6 microg/ml(-1) using this polarographic method with 1 ml urine made up to 10 ml with pH 10 buffer. Using cathodic stripping voltammetry and accumulating at a hanging mercury drop electrode at - 0.2 V for 30 s, linear calibration graphs were obtained from 0.35 to 40 microg/ml(-1) cefaclor in B-R buffer pH 10. A relative standard deviation of 4.2% (eta = 5) was obtained, and the limit of detection was calculated to be 2.9 ng/ml(-1). Direct determination of cefaclor in human urine (1 ml of urine was made up to 10 ml with pH 10 buffer) spiked to 0.39 microg/ml(-1) was made (recovery 98.6%).

Cefaclor↗
PubMed2002

The characteristics of a wire-plane corona streamer detector when an alpha-particle source is moved in a plane parallel to the cathode.

The operation characteristics of a wire-plane corona streamer detector (WPCSD) in open air were investigated for broad side irradiation. Investigations were made on the counting characteristics in relation to their dependence on various anode diameters and source-anode spacing. The onset voltages for the corona mode Vo as well as for the spark mode Vp were determined. For each wire diameter a streamer mode (Vp - Vo) was found. The sensitivity of the WPCSD was studied when a collimated beam of a-particles was moved parallel to the plane of the cathode from the anode-wire toward the cathode. In addition, the pulse height spectra of alpha-particles incident on the detector for different values of the anode voltage, Va, were determined and studied. A qualitative interpretation of the experimental data was given.

Journal Article↗
PubMed2000

Ultrasonic effects on electroorganic processes. Part 17. Product selectivity control in cathodic reduction of acrylonitrile

Product selectivity for adiponitrile, which was formed as the corresponding hydrodimeric product along with propionitrile as the hydromonomeric product in the cathodic reduction of acrylonitrile, was significantly increased under ultrasonic irradiation with an intensity above the ultrasonic cavitation threshold. This ultrasonic effect is rationalized as due to mass transport promotion of acrylonitrile molecules to the cathode surface from the bulk electrolytic solution by high speed jet streams caused by the cavitation. A mechanism for the ultrasonic effect is discussed in detail on the basis of the reaction pathway of the hydrodimerization of acrylonitrile.

Journal Article↗
PubMed2003

Level of action of cathodal DC polarisation induced inhibition of the human motor cortex.

OBJECTIVE: To induce prolonged motor cortical excitability reductions by transcranial direct current stimulation in the human. METHODS: Cathodal direct current stimulation was applied transcranially to the hand area of the human primary motor cortex from 5 to 9 min in separate sessions in twelve healthy subjects. Cortico-spinal excitability was tested by single pulse transcranial magnetic stimulation. Transcranial electrical stimulation and H-reflexes were used to learn about the origin of the excitability changes. Neurone specific enolase was measured before and after the stimulation to prove the safety of the stimulation protocol. RESULTS: Five and 7 min direct current stimulation resulted in motor cortical excitability reductions, which lasted for minutes after the end of stimulation, 9 min stimulation induced after-effects for up to an hour after the end of stimulation, as revealed by transcranial magnetic stimulation. Muscle evoked potentials elicited by transcranial electric stimulation and H-reflexes did not change. Neurone specific enolase concentrations remained stable throughout the experiments. CONCLUSIONS: Cathodal transcranial direct current stimulation is capable of inducing prolonged excitability reductions in the human motor cortex non-invasively. These changes are most probably localised intracortically.

Adult↗
PubMed1990

Laser-excited atomic fluorescence in a pulsed hollow-cathode glow discharge.

A pulsed glow discharge with low background noise is evaluated as an atom reservoir for laser-induced atomic fluorescence spectroscopy. Aqueous solutions are dried in graphite electrodes that are used as disposable hollow cathodes. Atomic vapor is produced in a flowing-gas glow discharge with a water-cooled cathode holder. A dye laser triggers a switching circuit that pulses that glow discharge, and fluorescence measurements are made 100 microseconds after the discharge is extinguished. The atomic population is large during this dark period, while the background emission is negligible. Linear calibration curves are obtained by nonresonance fluorescence for two elements, Pb and Ir. The detection limits for Pb are 100 pg/mL and 500 fg, and for Ir are 6 ng/mL and 20 pg. The experimental detection limit for Pb is compared to the intrinsic detection limit.

Lasers↗
PubMed2003

A two-channel microfluidic sensor that uses anodic electrogenerated chemiluminescence as a photonic reporter of cathodic redox reactions.

This paper describes a new approach for sensing electrochemically active substrates in microfluidic systems. This two-electrode sensor relies on electrochemical detection at one electrode and electrogenerated chemiluminescent (ECL) reporting at the other. Each microfabricated indium tin oxide electrode is located in a separate microfluidic channel, but the channels are connected downstream of the electrodes to maintain a complete electrical circuit. Because of laminar flow, there is no bulk mixing of the fluids in the detecting and reporting channels. This approach allows the ECL reaction to be physically and chemically decoupled from the sensing channel of the device, which greatly expands the number of analytes that can be detected. However, because the cathode and anode are connected, electron-transfer processes occurring at the sensing electrode are electrically coupled to the ECL reaction. Charge balance permits the ECL light output to be quantitatively correlated to electrochemical reductions at the cathode. The system is used to detect Fe(CN)6(3-), Ru(NH3)6(3+), and benzyl viologen and report their presence via Ru(bpy)3(2+) (bpy = bipyridine) luminescence. Each different redox target initiates ECL at a unique potential bias related to its standard redox potential. The influence of the concentrations of Ru(bpy)3(2+) and the target analytes is discussed.

Journal Article↗
PubMed2003

Total protein determinations by particle beam/hollow cathode optical emission spectroscopy.

A novel method for quantitative total protein determinations is presented. Total protein content is determined by particle beam/hollow cathode optical emission spectroscopy (PB/HC-OES) through monitoring of carbon atomic emission. The PB/HC-OES offers such advantages as ease of operation, exclusion of labor-intensive sample pretreatment processes, rapid analysis, high sensitivity, and low detection limit. The method could also be adapted to be integrated to current microfluidics devices. Parametric optimization for sample introduction, nebulization, desolvation, and hollow cathode source conditions is performed for the analysis of aqueous bovine serum albumin solutions. Response curves of C (I) 193.0-nm emission were obtained under the optimized conditions with both 10% HCl and 100 micromL KCl added to the sample matrix as potential carriers. The detection limit for triplicate injections of bovine serum albumin standards was found to be on the single-nanogram level with 200-microL injections. The addition of KCl significantly improved the sensitivity, supporting the proposed "carrier effect" of chloride salts in the particle transport process. Results obtained here suggest a range of applications for the use of the PB/HC-OES source for total protein determinations; emphasis here is future use in assessing protein quantification in microfluidic systems.

Electrodes↗
PubMed2001

Tervalent conducting polymers with tailor-made work functions: preparation, characterization, and applications as cathodes in electroluminescent devices.

A series of conducting polymers have been prepared through thermal polymerization of transition-metal diimine complexes. The as-polymerized material is electrochemically converted into its formally zerovalent form. Due to the proximity of the half-wave potentials of the formal 1+/0 and 0/1- couples, there is substantial disproportionation of the redox sites at room temperature, resulting in a conductive tervalent mixed-valent material. The redox processes that give rise to this mixed-valent material are predominantly ligand-based, and therefore are highly sensitive to substitution on the ligand periphery. Solution redox chemistry of the monomer can be used to accurately predict the work function of the corresponding zerovalent conducting polymer, which has been verified by ultraviolet photoelectron spectroscopy. Many of these materials have especially low work functions (<3.6 eV) making them appropriate materials to use as cathode materials in organic light-emitting devices (OLEDs). Working examples of tris(8-hydroxyquinoline)aluminum(III)-based OLEDs have been fabricated using one of these polymers as a cathode.

Journal Article↗
PubMed2003

Nanopatterning of alkynes on hydrogen-terminated silicon surfaces by scanning probe-induced cathodic electrografting.

The electrochemical cathodic electrografting reaction, previously demonstrated on bulk silicon surfaces, can be patterned on the nanoscale utilizing conducting probe atomic force microscopy (CP-AFM). Alkyne electrografting is a particularly useful chemical technique since it leads to direct covalent attachment of conjugated alkynes to silicon. In addition, application of a forward bias during the reaction renders the surface less sensitive to oxidation and the resulting monolayers are very stable in air and basic aqueous solution. Alkyne monolayer lines can be drawn down to 40 nm resolution using a Pt-coated AFM tip, and the heights of the monolayers scale with the molecular length of the alkyne. The tip is biased (+) and the surface is biased (-) to drive the cathodic electrografting reaction under ambient conditions. The resistance of the monolayers to fluoride, as well as friction force microscopy, indicate that the alkynes are covalently bonded to the surface, not oxide-based, and hydrophobic. The reaction does not work with alkenes, and therefore hydrosilylation is not the primary mode of reaction. Wider lines (300 nm) can be produced using broadened Pt-coated AFM tips. This reaction could be important for the interfacing of conjugated molecules directly to silicon in a spatially controlled fashion.

Journal Article↗
PubMed1996

Comparative Studies of Cathodically-Promoted and Base-Catalyzed Michael Addition Reactions of Levoglucosenone.

Regioselective Michael addition of nitro and heterocyclic compounds to levoglucosenone, 1, is effectively catalyzed by amines and also by cathodic electrolysis. In comparison to the base-catalyzed reaction, it was found that under electrochemical conditions the reaction proceeds under milder conditions and with higher yields. Cathodically-initiated Michael addition of thiols to levoglucosenone using small currents produces the previously unknown threo addition product in several instances. The normal erythro isomer, identified as the kinetic product, tends to be formed when large currents are used. In contrast, slow, low current electrolyses promote equilibration of the two forms so that erythro can be converted to threo by the retro reaction and readdition. Addition of 2-naphthalenethiol to (R)-(+)-apoverbenone is also reported.

Journal Article↗
PubMed2005

Carbon nanotube film by filtration as cathode catalyst support for proton-exchange membrane fuel cell.

A simple filtration method is developed to prepare a partially oriented superhydrophobic film of carbon nanotubes (CNTs) that have been catalyzed with uniform small Pt nanoparticles (2.8 nm) at high metal loading (30 wt %). A proton-exchange membrane fuel cell with the oriented CNT film as the cathode achieves higher single-cell performance than those with carbon black and a disordered CNT-film-based cathode probably because of the enhanced electrocatalytic activity of Pt/CNT and improved mass transport within the oriented film.

Journal Article↗
PubMed1997

Cathodic stripping voltammetric determination of doxazosin in urine and pharmaceutical tablets using carbon paste electrodes.

Several voltammetric techniques were used to explore the reductive behaviour of the antihypertensive agent doxazosin on a bare carbon paste (CPE) and a Tenax-modified carbon paste electrode (TMCPE). The results indicate that the process is irreversible and fundamentally controlled by adsorption, which allows doxazosin to be accumulated at the electrode surface. The cathodic adsorptive stripping (AdS) response was evaluated with respect to pH, accumulation variables and instrumental parameters, using differential-pulse (DPV) and square-wave voltammetry (SWV) as redissolution techniques. In both cases, a voltammetric peak close to 0 V in Britton-Robinson buffer (pH 6.6) was obtained after a preconcentration step at 0.55 V for 3 min (2000 rpm) and a subsequent cathodic scan. When the TMCPE was used, the limits of detection were 4.35 x 10(-11) and 5.18 x 10(-11) M for AdS-DPV and AdS-SWV, respectively. The deposition time (3 min) was improved relative to that obtained by means of CPE (6 min). Under the optimum operational conditions, the doxazosin reduction peak showed a linear response in the range from 6 x 10(-11) to 1 x 10(-9) M by using AdS-DPV, with an RSD of 3.39% for 3 x 10(-8) M doxazosin solution (n = 10). A method was developed for the determination of doxazosin in human urine and formulations.

Adsorption↗
PubMed1994

Determination of selenium in food supplements by differential-pulse cathodic stripping voltammetry in the presence of added copper.

Selenium was determined by cathodic stripping voltammetry in a 1 mol l-1 HCl acid solution containing added CuII. In this medium, selenium was preconcentrated on the hanging mercury drop electrode and stripped cathodically in differential-pulse mode. After a deposition period of 1 min, 0.2 ng ml-1 of selenium could be detected. The method was applied to the analysis of food supplements. Total selenium was determined after digestion of the sample with HNO3-HClO4 and reduction to the electroactive SeIV by heating with HCl. Inorganic selenium (i.e., selenite and selenate) was similarly determined after extraction with dilute sodium hydroxide solution and clean-up on activated carbon. Representative over-the-counter preparations have been analysed.

Copper↗
PubMed2005

Direct optical emission spectroscopy of liquid analytes using an electrolyte as a cathode discharge source (ELCAD) integrated on a micro-fluidic chip.

Atomic emission detection of metallic species in aqueous solutions has been performed using a miniaturised plasma created within a planar, glass micro-fluidic chip. Detection was achieved using an Electrolyte as a Cathode Discharge source (ELCAD) in which the sample solution itself is used as the cathode for the discharge. To realise the ELCAD technique within a micro-fluidic device, a parallel liquid-gas flow was set up in a micro-channel and a glow discharge ignited between the flowing liquid sample surface and a metal wire anode. The detection of copper and sodium was achieved, using atmospheric pressure air as a carrier gas, by observation of atomic emission lines of copper at 324 nm, 327 nm, 511 nm, 515 nm and 522 nm and an atomic emission line of sodium at 589 nm using a commercially available miniaturised spectrometer. A total electrical power of less than 70 mW was required to sustain the discharge. A semi-quantitative, absolute detection limit of 17 nmol s(-1) was obtained for sodium with a sample flow rate of 100 microL min(-1) and an integration time of 100 ms in air at atmospheric pressure. The volume required for such detection is approximately 170 nL. Further analysis was performed with an Echelle spectrometer using both argon and air as a carrier gas. The geometry and flow rates used demonstrate the feasibility of integrating such micro-plasmas into other micro-fluidic devices, such as miniaturised CE devices, as a method of detection. The potential for using such micro-plasmas within highly portable miniaturised systems and mu-TAS devices is presented and discussed.

Journal Article↗
PubMed2006

Cathodic chemistry of high performance Zr coated alkaline materials.

A low level zirconia modification significantly stabilizes alternative higher energy cathodes under consideration to improve the energy storage capacity of alkaline batteries, and is demonstrated on materials including periodate, Fe(VI) "super-iron", manganese, nickel, bismuthate and silver oxide cathodes.

Journal Article↗