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At least 1,243 records · Page 69Linked to original sources
PubMed2004

Micellar electrokinetic chromatography at low pH with polyelectrolyte-coated capillaries.

The performance of capillaries coated with a poly(diallyldimethylammonium) (PDADMA) monolayer or poly(diallyldimethylammonium)-poly(styrenesulfonate) bilayer was investigated and compared under micellar electrokinetic chromatographic (MEKC) conditions. Both monolayer (positively charged) and bilayer (negatively charged) coatings with micellar (sodium dodecyl sulfate) electrolyte generated very stable and pH-independent cathodal electroosmotic flow (EOF). From the results obtained, it can be concluded that in a doubly coated capillary the second poly(styrenesulfonate) layer is replaced by sodium dodecyl sulfate micelles during flushing with micellar electrolyte. Consequently, in order to obtain a stable and pH-independent cathodal electroosmotic flow for the MEKC separations, the capillary coating with the second polyanion layer is not necessary. The importance of the PDADMA coating was illustrated by comparing MEKC separations of the common developing agents (hydroquinone, phenidone, pyrocatechol, pyrogallol and quinone) on a bare uncoated capillary with the coated capillary. The coating provides reproducible MEKC separations at low pH (pH 3.0) with relative standard deviation (R.S.D.) values for migration times and peak areas lower than 0.45 and 3.3%, respectively. Good linearities in the range from 5 x 10(-5) to 2 x 10(-3) mol l(-1) were obtained for all five compounds, with correlation coefficients higher than 0.998. The detection limits were in the range from 5 x 10(-6) mol l(-1) for pyrocatechol to 2 x 10(-5) mol l(-1) for quinone. The proposed MEKC system was applied to the determination of hydroquinone and phenidone in X-ray photographic developer solutions.

Calibration↗
PubMed2004

Vestibular testing by electrical stimulation in patients with unilateral vestibular deafferentation: galvanic evoked myogenic responses testing versus galvanic body sway testing.

OBJECTIVE: To investigate the agreement of a lesion site as indicated by two different vestibular tests with electrical stimulation, galvanic body sway testing (GBST) and galvanic evoked myogenic responses (galvanic vestibular evoked myogenic potential; galvanic VEMP) testing, in patients with unilateral vestibular deafferentation. METHODS: Nineteen patients with unilateral vestibular deafferentation were studied, and the criteria for patient selection were as follows: (1) absence of a caloric response to ice water on the affected side in a supine position, and (2) absence of VEMP to 95 dBnHL clicks on the affected side. We assessed the postural response of the subjects to long duration galvanic stimulation (1 mA, 5 s) by measuring the lateral displacement at the center of foot pressure with a cathode electrode on the forehead, and an anode electrode on the mastoid (GBST). We also recorded the electromyographic (EMG) activities of the sternocleidomastoid muscle (SCM) to short duration galvanic stimulation (3 mA, 1 ms) (galvanic VEMP) with a cathode electrode on the mastoid, and an anode electrode on the forehead. RESULTS: In 18 of the 19 patients, the lesion site indicated by GBST was identical to that indicated by galvanic VEMP. Fourteen patients had abnormal results in both tests while 4 patients had normal results in both tests. One patient with acoustic neuroma had normal results in GBST but abnormal results in galvanic VEMP. CONCLUSIONS: These results suggest that electrical stimulation in these two tests stimulates the same area of the peripheral vestibular afferent system, although the duration of stimulation was different, and that the estimate of the lesion site indicated by these tests in patients with complete or nearly complete unilateral vestibular damages is reliable. SIGNIFICANCE: These results suggest that short-duration galvanic stimulation as well as long-duration galvanic stimulation stimulates the vestibular system at the same level.

Adult↗
PubMed2006

Depth electrode recorded cerebral responses with deep brain stimulation of the anterior thalamus for epilepsy.

OBJECTIVE: We investigated the relation between anterior thalamic stimulation and the morphology of the evoked cerebral responses (CRs) using intracerebral depth electrodes in patients with intractable epilepsy undergoing deep brain stimulation (DBS) of the thalamus. METHODS: Monopolar cathodic and bipolar stimuli were delivered at a rate of 2 or 1 Hz to the anterior nucleus (AN) and the dorsomedian nucleus (DM) of two patients using the programmable stimulation device (Medtronic ITREL II) or a GRASS stimulation device (S12). CRs were recorded from depth or DBS electrodes, situated bilaterally in mesial temporal (hippocampus, both patients), lateral temporal (one patient), orbitofrontal (Brodmann area 11, one patient) and anterior thalamic sites (one patient). RESULTS: The distribution and morphology of the CRs depended primarily on the site of stimulation within the anterior thalamic region. Overall, monopolar cathodic and bipolar stimulation of the AN elicited CRs mainly in ipsilateral mesial temporal cortical areas, whereas stimulation of the DM evoked high-amplitude CRs predominantly in ipsilateral orbitofrontal areas. The amplitude of the CR was positively related to the strength of the stimulus and generally higher with monopolar than with bipolar stimulation. The differences between CRs elicited during wakefulness or slow wave sleep were minimal. CONCLUSIONS: The distribution of the CRs corresponded with the intracerebral pathways of the involved structures and the findings are in good accordance with those of our previous study investigating the sources of CRs using statistical non-parametric mapping of low resolution electromagnetic tomography (LORETA) values. SIGNIFICANCE: Our findings indicate a certain degree of point-to-point specificity within the thalamocortical circuitry, which may make optimal localization of DBS electrodes important in patients with epilepsy.

Adult↗
PubMed2005

Corrosion behavior of Cu and the Cu-Zn-Al shape memory alloy in simulated uterine fluid.

Chemical immersion tests, electrochemical methods and atomic absorption spectrometry were employed to investigate the corrosion behavior of Cu and the Cu-Zn-Al shape memory alloy (SMA) in simulated uterine fluid. The effect of pH on corrosion rate and corrosion potential was also investigated. The results indicated that in the static state in simulated uterine fluid, dealuminumification of the Cu-Zn-Al alloy occurred with Cl- combining with aluminum ions to form hydroxyl aluminum chloride. The hydroxyl aluminum chloride hydrolyzed readily and facilitated further dealuminumification corrosion. The corrosion process of Cu and Cu-Zn-Al SMA in simulated uterine fluid was controlled by cathodic reduction of oxygen. Because the tendency for surface ionization is greater for aluminum than for zinc, a compact protective aluminum layer was formed, which inhibited the cathodic reduction of oxygen. Hence, the corrosion rate of Cu-Zn-Al SMA was smaller than that of Cu in simulated uterine fluid. With increasing pH, the corrosion rate of Cu and Cu-Zn-Al SMA in simulated uterine fluid decreased and the open-circuit potential moved in a positive direction.

Alloys↗
PubMed2005

Square-wave stripping voltammetry for direct determination of eight heavy metals in soil and indoor-airborne particulate matter.

The application of square-wave voltammetry (SWV) for the determination of eight elements viz. Cd(II), Pb(II), Cu(II), Zn(II), Co(II), Ni(II), Cr(VI), and Mo(VI) in soil and indoor-airborne particulate matter has been examined and optimized. The cathodic and anodic types of the SWV technique were examined for the detection of these metal ions. It was found that the square-wave anodic stripping voltammetry is the conventional technique for the determination of Zn(II), Cd(II), Pb(II), and Cu(II), but square-wave adsorptive cathodic stripping voltammetric method is used for the determination of Co(II), Ni(II), Mo(VI) and Cr(VI). Various experimental parameters, which influenced the response of the mercury film electrode to these metal ions, were optimized. The detection limits of these metal ions were 0.03, 0.4, 0.04, 0.1, 0.15, 0.05, 0.2, and 3.2 microg/kg for Cd(II), Pb(II), Cu(II), Zn(II), Co(II), Ni(II), Cr(VI), and Mo(VI), respectively, with very good accuracy (standard deviation is below 2%). Interference from coexisting ions was successfully investigated. A comparison of analytical data for analyzing real samples was carried out between the SWV method and the graphite furnace atomic absorption spectrophotometric (GFAAS) method. By the standard addition method, the recoveries were 96.6-104% with SD of 0.75-2.5%. The great advantage of SWV is the simplicity, selectivity, sensitivity, and shortening analysis time over the GFAAS method.

Air Pollutants↗
PubMed2005

Effect of lactic acid and iontophoresis on drug permeation across rabbit ear skin.

The aim of this paper was to explore the efficacy of lactic acid as permeation enhancer for drug molecules across the skin. Three model permeants were chosen: acetaminophen (non-ionized), buspirone hydrochloride (cationic drug) and ibuprofen lysine (anionic drug). We also explored the association of lactic acid and iontophoresis as a means of enhancing drug delivery. Permeation experiments were performed in vitro, using rabbit ear skin as barrier. The results obtained indicate that lactic acid has some effects on model drug permeation across the skin. The effect was more evident with the anionic drug ibuprofen. Cathodal intophoresis increased ibuprofen transport, but when lactic acid was associated with cathodal iontophoresis, a concentration-dependent reduction of ibuprofen iontophoretic flux was observed, probably for the competition by the co-ion. The application of electric current (anodal iontophoresis) to a solution of acetaminophen produced an increase in its transport, due to the presence of an electroosmotic contribution; however, the effect of the association of anodal iontophoresis and lactic acid produced no further enhancement.

Acetaminophen↗
PubMed2004

Effect of surfactants on the rate of solid-liquid mass transfer with gas generation at the interface.

The effect of Triton X-100 (nonionic surfactant) and cetyltrimethylammonium bromide (CTAB), cationic surfactant, on the mass transfer coefficient of the cathodic reduction of ferricyanide ions and anodic oxidation of ferrocyanide ions at hydrogen- and oxygen-evolving electrodes, respectively, was studied. It was found that the limiting current decreases by amounts ranging from 26.67 to 54.67% for Triton X-100 and from 20 to 46.0% for CTAB in the case of cathodic reduction of ferricyanide ions under natural convection at H2-evolving electrodes and from 23.81 to 51.43% for Triton X-100 and from 18.10 to 40.95% for CTAB in the case of anodic oxidation of ferrocyanide ions under natural convection at O2-evolving electrodes, depending on the concentration of surfactant. Also the effects of Triton X-100 and CTAB on the gas hold-up and cell voltage were studied. The presence of surfactant in electrolytes was found to decrease the mass transfer coefficient by an amount ranging from 5.37 to 95.9%, depending on the operating conditions. Gas hold-up, cell voltage, and power consumption were found to increase in the presence of surfactant.

Journal Article↗
PubMed2005

Preparation and characterization of LiMn2-yCoyO4 spinels by low heating solid state coordination method.

Cathode material LiMn2-yCoyO4 spinels were prepared by annealing the mixed precursors, which were synthesized by a low heating solid state coordination method using lithium acetate, manganese acetate, cobalt acetate, and oxalic acid as original materials. The structures and morphologies of the LiMn2-yCoyO4 spinels were investigated as a function of annealing temperature and time. The results showed that all samples in different annealing temperature and time had the same spinel structure. There were some growth and agglomeration in the particles when annealing temperature increased from 450 to 650 degrees C. And the crystal structure was more perfect at the upper temperature. In addition, the electrochemical properties of LiMn2-yCoyO4 spinels used as cathode material for lithium-ion batteries were studied in detail in this paper.

Journal Article↗
PubMed2005

Enhancement of the electrochemical properties of LiMn2O4 through Al3+ and F- co-substitution.

The cathode-active materials LiMn2O4, LiAl0.1Mn1.9O4, and LiAl0.1Mn1.9O3.9F0.1 were synthesized by a microwave-assisted sol-gel method. The influence of different doping elements on the structural and electrochemical properties of the as-prepared samples was investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical experiments. The results indicated that fluorine plays an important role in controlling the morphology, and the doped aluminum could enhance significantly the stability of spinel-type LiMn2O4. The initial discharge capacity of the Al3+ and F- co-substituted specimen reached 129.8 mA h/g and has a high capacity retention after 40 cycles. The outstanding electrochemical properties of LiAl0.1Mn1.9O3.9F0.1 make it a possible promising cathode material for lithium-ion batteries.

Journal Article↗
PubMed2006

Interdependence of virtual electrode polarization and conduction velocity during premature stimulation.

BACKGROUND: Fiber orientation in the heart plays a crucial role in the anisotropic nature of impulse propagation and the formation of virtual electrode polarization (VEP). The relationship between anisotropic conduction velocity and VEP is not fully understood. METHODS AND RESULTS: We recorded transmembrane potential from the surface of isolated rabbit hearts (N = 7) in the presence of 15 mmol/L of diacetylmonoxime using a video imaging system. We paced each heart at a constant cycle length of 250 milliseconds and delivered a premature stimulus (S2) from the same unipolar electrode. The S2 pulses of either polarity were applied at various coupling intervals (CIs); S2 duration was 10 milliseconds and stimulus amplitude was 40 mA. Impulse propagation at 250 milliseconds occurred via elliptical waves with an anisotropy ratio (AR) of approximately 2.5. Owing to VEP, AR varied dramatically as a function of S2 polarity and CI. At intermediate CIs (approximately 150 milliseconds), AR was decreased by a factor of 3 for anodal stimulation and increased by a factor of 2 for cathodal stimulation. At slightly shorter CIs (approximately 115 milliseconds), impulse propagation was blocked, leading to unidirectional block and the initiation of reentrant arrhythmias. Conduction block always occurred along fibers for anodal stimulation and across fibers for cathodal stimulation. CONCLUSION: Fiber orientation plays a prominent role in impulse propagation during premature stimulation such as that which occurs during pacing of ventricular tachycardia and ventricular fibrillation. The interdependence of VEP and conduction velocity acts to dramatically alter AR and arrhythmogenesis.

Action Potentials↗
PubMed2004

Effect of different extracting solutions on the electrodialytic remediation of CCA-treated wood waste Part I. Behaviour of Cu and Cr.

Removal of Cu and Cr from chromated copper arsenate (CCA)-treated wood waste under batch electrodialytic conditions was studied. The effect of different types of extracting solutions, such as deionised water or aqueous solutions of NaCl, formic acid, oxalic acid, and EDTA, on the magnitude and direction of the fluxes of Cu- and Cr-containing species in the electrodialytic cell was investigated. Oxalic acid was found to have the best performance if simultaneous removal of the two elements is required (removal efficiencies of 80.5% for Cu and 87.4% for Cr, respectively). A mixture of oxalic acid and formic acid also led to similar removal efficiencies. In these experiments, the target elements were accumulated in both the anode and cathode compartments of the electrodialytic cell due to the formation of negatively charged complexes with the organic acids used besides the free cationic forms. The latter were not present if EDTA was the extracting solution resulting in directing the Cu and Cr fluxes to the anode compartment. Contrary, these fluxes were exclusively to the cathode compartment if deionised water or an aqueous solution of NaCl were used. These extracting solutions proved suitable for solubilising (re-mobilisation) of Cu but were less efficient for Cr removal (less than 20% removal). Overall, the results obtained show the important role of the proper selection of the type and composition of the extracting solution for the success of subsequent electrodialytic removal of Cu and Cr from CCA-treated wood waste.

Chelating Agents↗
PubMed2004

An overview of recycling and treatment of scrap computers.

In order to recover valuable materials and to minimize the adverse effects of hazardous materials contained in scrap computers, a dismantling practice is commonly adopted to treat scrap computers. By using the dismantling process, both useful and hazardous materials can be manually separated and retrieved. On the basis of the properties of the retrieved materials, they can be sent to appropriate facilities for further recycling or treatment. Among the retrieved materials, the treatment of hazardous materials from cathode ray tubes (CRT) and printed circuit boards with integrated circuits have drawn considerable attention, thus implying that the proper treatment of such materials can greatly assure the successful recycling of scrap computers. For this reason, this study reviews the available technologies which can be applied to treat and recycle cathode ray tube components and printed circuit boards with integrated circuits. Actual recycling data from a scrap computer recycling plant located in Taiwan are also introduced. The data show that this recycling plant can recover 94.75 wt. % and 45.99 wt. % of useful materials from the main machines (i.e., CPU, power supplier, fan, IC boards, DVD drive, CD drive, hard disk, soft disk, shell casing, etc.) and monitors of scrap computers, respectively.

Computers↗
PubMed2005

Assessing effect of electrode configuration on the efficiency of electrokinetic remediation by sequential extraction analysis.

The electroremediation experiments were conducted on artificially polluted soils by introducing a single metallic contaminant (Pb, Zn and Cu) and multiple metallic contaminants (Pb+Zn+Cu). Based on sequential extraction results, it was observed that the removal efficiencies of lead, zinc and copper vary depending on types of contamination. When the soil was contaminated only by lead, the removal efficiency was found to be 48%. However, the removal efficiency of lead decreased to 32% when the soil was contaminated by the combination of lead, zinc and copper. Similar results were observed for zinc and copper. The corresponding removal efficiency values for zinc and copper were 92% and 37%, and 34% and 31%, respectively. Effects of electrode geometry on the removal efficiency of metals were investigated by constructing a multiple anode arrangement. In this arrangement, the electrokinetic unit consists of three cylinders, which lie one inside the other, and the soil was placed in the middle cylinder. The central cylinder was the cathode well and the outer cylinder was the anode well, where eight identical anode electrodes were placed in octagonal with respect to the cathode electrode. By using this electrode arrangement in removal of metals from the soil contaminated with the combination of three metals (Pb+Zn+Cu), the removal efficiencies of lead, zinc and copper were found to be 29%, 18% and 18%, respectively. As it can be seen, these numerical values are much lower than the values that were obtained when the traditional two-plate electrode arrangement used in the electroremediation experiments (32%, 37% and 31%).

Copper↗
PubMed2005

Evaluation of electrokinetic removal of heavy metals from sewage sludge.

The presence of heavy metals is one of the main obstacles for agricultural use of million tonnes of dewatered sewage sludge produced in wastewater treatment plants. Electrokinetic (EK) treatment can be applied to remove heavy metals from sludge. The aim of this study was to increase the efficiency of electrokinetic removal of heavy metals from dewatered sewage sludge. EK experiments were carried out with and without pH adjustment in cathode chamber of acidified sewage sludge. The selective sequential extraction (SSE) was used to determine the fractionation of heavy metals in sewage sludge. The mobility of heavy metals in sludge significantly increased after its acidification at pH 2.7 and followed the order: Ni, Zn, Cu, As, Cr, Pb. Removal efficiencies of heavy metals in the experiment with acidified sewage sludge and pH adjustment at cathode chamber at 2.0 were: 95% for Zn, 96% for Cu, 90% for Ni, 68% for Cr, 31% for As and 19% for Pb. The concentrations of Zn, Cu, Ni, Cr and Pb after EK treatment were below the United States Environmental Protection Agency limits for biosolids applied to agricultural land, forest, public contact sites or reclamation sites.

Chemical Fractionation↗
PubMed2006

Use of carbon stable isotope to investigate chloromethane formation in the electrolytic dechlorination of trichloroethylene.

Carbon stable isotope trichloroethylene ((13)C TCE) was used to investigate the formation of chloromethane (CM) during the electrolytic dechlorination of trichloroethylene (TCE) at a granular-graphite packed cathode. A method was developed to use a conventional GC/MS to analyze and quantify regular and (13)C TCE and their dechlorination products. The concentration of a (13)C compound can be calculated, based on the concentration of its regular counterpart, from the response ratio of two fragments of different mass per charge values from the compounds in a sample and two characteristic MS spectrum ratios: one is the response ratio of the two fragments of the regular compound, and the other is the response ratio of the corresponding fragments of the regular and (13)C compounds at the same concentrations. The method was used to analyze the regular and (13)C compounds observed in an experiment of dechlorination in an ammonium acetate solution that contained both regular TCE and (13)C TCE. Results of analysis confirmed that CM was not a direct product of TCE dechlorination at the granular graphite cathode that cis-DCE was an intermediate product of TCE dechlorination, and that 1,1-DCE was not a dechlorination product.

Carbon Isotopes↗
PubMed2006

Electric pulp tester conductance through various interface media.

A conducting media is necessary when using an electric pulp tester (EPT). The objective of this study was to observe differences in conductance through various media. We hypothesized that variations in current conductance through different media exist. The pulp chamber of a freshly extracted premolar was exposed, and the cathode of a voltmeter was inserted into the pulpal tissue. The anode was coupled to the EPT handpiece. The measurement taken during dry (no interface media) EPT tip-to-tooth contact was 0 V, which served as negative control. EPT tip directly touching the cathode measured 3.9V and served as positive control. A number of media readily available in the dental office were tested. Data was analyzed using single factor ANOVA. Listerine (3.3) conducted the most voltage (p<0.5). Of nonliquids, K-Y Brand UltraGel and Crest Baking Soda & Peroxide Whitening Tartar Control toothpaste recorded significantly (p<0.05) higher voltage readings (1.4 V).

Bicuspid↗
PubMed2006

Stripping voltammetric quantification of the anti-diabetic drug glipizide in bulk form and pharmaceutical formulation.

The electrochemical behavior of glipizide at the hanging mercury drop electrode (HMDE) was studied in B-R universal buffers of pH 1.7-11. The voltammograms exhibited a well-defined 4-electron irreversible cathodic peak which attributed to reduction of the two C=N of the pyrazine ring of glipizide molecule. Glipizide was found to has an interfacial adsorptive character onto the mercury electrode surface. A monolayer surface coverage of 1.02x10(-10)mol cm(-2) was estimated and hence each adsorbed glipizide molecule occupied an area of 1.63 nm(2) onto the mercury electrode surface. A simple and precise square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure was described for quantification of bulk glipizide with a limit of detection of 1.5x10(-10)M and a limit of quantitation of 5x10(-10)M. The proposed procedure was successfully applied for quantitation of glipizide in its pharmaceutical formulation (Minidiab tablets) without interference from excipients.

Buffers↗
PubMed2004

Facile synthesis of chlorophyll analog possessing a disulfide bond and formation of self-assembled monolayer on gold surface.

A chlorophyll analog forming self-assembled monolayers (SAMs) on a gold surface was synthesized for the first time. 13(2)-(Demethoxycarbonyl)pheophorbide-a, which was converted from naturally occurring chlorophyll-a, was condensed with 2-hydroxyethyl disulfide to give a chlorin dyad linked by a disulfide bond. The chlorin analog was spontaneously immobilized on a gold substrate by soaking in an acetone solution of the dyad for 24 h. The resulting gold plate exhibited a visible absorption spectrum with about 420- and 675-nm maxima as the Soret and Qy peaks, respectively, indicating that chlorin pi-conjugates were modified on the gold substrate through Au-S bonding. Both visible absorption and fluorescence emission bands of the chlorin chromophores on the gold substrate were red-shifted compared with those of the synthesized chlorin dyad in a homogeneous acetone solution. The measured absorbance at the Soret maximum suggests that the chlorin chromophores on the gold plate were densely packed on a gold surface to form a SAM. Cathodic photocurrents were generated from SAMs of the chlorins on a gold substrate with irradiation of visible-lights above 400 nm. Photoinduced electron transfer from chlorins on the gold substrate to oxygen molecules in an electrolyte solution were attributed to the cathodic photocurrent generation.

Chlorophyll↗