SEARCH · PubMed Health

Results for “Graphite”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources

PubMed2006

New electrodes for old: from carbon nanotubes to edge plane pyrolytic graphite.

Different types of carbon based electrodes have emerged over the last few years, significantly changing the scope and sensitivity of electro-analytical methods for the measurement of diverse targets from metal ions through gases to biological markers. This Highlight article shows how the use of carbon nanotube modified electrodes has led to a fundamental understanding of the location and nature of electron transfer processes on graphitic electrodes and to the realisation that edge plane pyrolytic graphite may represent, at present, an optimal electrode material of this type for electroanalysis.

Carbon↗

PubMed2006

Nucleation and growth of cobalt nanostructures on highly oriented pyrolytic graphite.

Cobalt in the form of three-dimensional (3D) hemispherical clusters (size approximately 10-30 nm) were observed to grow on pristine graphite surfaces via a Volmer-Weber growth mode. X-Ray photoelectron spectroscopy (XPS) reveals that these clusters are physisorbed on the surface. In the presence of minute surface contamination, the morphology of Co changes into a mixture of irregular and hemispherical three-dimensional islands. The formation of irregular islands appears to be mediated by the chemical interactions between Co and the surface contaminants as evidenced from analysis of the carbon pi-pi* transitions. Further analysis of size distribution of Co nanoclusters grown on pristine surfaces shows a critical nucleus size of i* = 1, i.e. a Co dimer forms the smallest stable cluster on a pristine graphite surface.

Adsorption↗

PubMed2003

Atomic vacancy-induced friction on the graphite surface: observation by lateral force microscopy.

Lateral force microscopy has been employed to investigate the frictional behaviour of atomic vacancies on the graphite surface. Such a study was only made possible by the controlled expansion of originally single-atom vacancies into multiatom vacancies, employing oxygen plasma etching for this purpose. Enhanced friction was observed on the vacancy regions compared with pristine areas of graphite, the origin of which is examined and discussed.

Friction↗

PubMed2005

Incorporating a hydrophobic solid into a coarse grain liquid framework: graphite in an aqueous amphiphilic environment.

A method is presented for incorporating a solid into a coarse grain liquid model. From the fully atomistic solid-liquid site-site description the solid is replaced by an implicit potential. The liquid particles are then coarse grained by appealing to statistical mechanics and probability theory. The dimensionality problem which arises is overcome with an approximate treatment and a force field is derived for graphite interacting with an existing coarse grain liquid model. Water is considered separately by using the experimentally observed contact angle between a water droplet and a graphite surface. Finally, the solid is restored to an explicit representation to allow for different geometries.

Adsorption↗

PubMed2005

Mesoscopic self-organization of a self-assembled supramolecular rectangle on highly oriented pyrolytic graphite and Au(111) surfaces.

A self-assembled supramolecular metallacyclic rectangle was investigated with scanning tunneling microscopy on highly oriented pyrolytic graphite and Au(111) surfaces. The rectangles spontaneously adsorb on both surfaces and self-organize into well ordered adlayers. On highly oriented pyrolytic graphite, the long edge of the rectangle stands on the surface, forming a 2D molecular network. In contrast, the face of the rectangle lays flat on the Au(111) surface, forming linear chains. The structures and intramolecular features obtained through high-resolution scanning tunneling microscopy imaging are discussed.

Gold↗

PubMed2003

Biopersistence of graphite whiskers deposited in rat lungs by 4-week inhalation.

Rats were exposed to a new graphite whisker for 4 wk by inhalation. Mass and fiber concentrations were 8.3 +/- 2.2 mg/m3 and 151.7 +/- 78.8 fibers (F)/ml, respectively, and mass median aerodynamic diameter was 3.0 micro m. Geometric mean sizes of the original whiskers were 0.86 micro m diameter and 6.8 micro m length. Size distributions, numbers, and mass of deposited whiskers in rat lungs were measured at 4 days, 7 mo, and 12 mo after the end of the exposure. Lungs including the whiskers were digested with acids by microwaves, then filtered onto polycarbonate filters. The number of whiskers on the filters was counted and sizes were measured based on scanning electron microphotos, and the mass was analyzed by an x-ray diffractometer. Change in the number of whiskers in the lung was expressed as an exponential decay with time, and the longer whiskers (>20 micro m) tended to remain selectively in the lung after the 12-mo clearance. Mass of graphite whisker also decreased exponentially. Count median diameters and lengths (CMDs and CMLs) decreased gradually during clearance time, although CMDs did not decrease linearly. Morphological change of this whisker was very unique and characteristic; that is, the surface of the whiskers peeled away in the lung as a result of their stratified crystalline structure.

Administration, Inhalation↗

PubMed1993

A scanning tunnelling microscopy study of the formation and chemical activation of step defects on the basal plane of pyrolytic graphite.

Scanning tunnelling microscopy is used to monitor etching of the basal plane of highly orientated pyrolytic graphite by ozone, oxygen and nitric acid. These treatments are seen to produce numerous single and multilayer step defects. Subsequent modification of the graphite sheet edges flanking these cavities by cyanuric chloride, TiCl4 and other reagents is shown to activate the edges, thereby making them capable of covalently binding various molecules.

Acrylates↗

PubMed1963

HEPARIN BONDING ON COLLOIDAL GRAPHITE SURFACES.

Experiments on clotting, both in vitro and in vivo, showed that a colloidal graphite surface, when rinsed with a cationic, surface-active agent, was capable of bonding heparin. The resistance of this graphite-heparin surface to the formation of clots was far greater than plastic or silicone surfaces in comparable studies.

Ammonium Compounds↗

PubMed1998

Preventive measures reduce exposure to polycyclic aromatic hydrocarbons at a graphite electrode plant.

OBJECTIVE: This study assessed the efficacy of preventive measures in a graphite electrode plant aimed at reducing occupational exposure to polycyclic aromatic hydrocarbons (PAHs). METHODS: Electrode workers (n = 146) answered a questionnaire and provided an end of shift urine sample. Urinary 1-hydroxypyrene (1-hpur), a biological marker of exposure to PAHs, was measured by high performance liquid chromatography coupled with: (a) fluorescence detection. 1-Hydroxypyrene concentrations were compared with the concentrations measured before implementing the preventive measures; and (b) those of a control group of 54 men not occupationally exposed to PAHs. RESULTS: After implementation of preventive measures, median concentrations 1-hpur were significantly reduced in some groups of workers: by -24%, -37% and -30% in workers at the green electrode unit, one baking impregnation unit, and the laboratory, respectively. In workers at a second baking impregnation unit, in end product finishing and in the power station 1-hpur concentrations were unchanged. Urinary 1-hp concentrations were still significantly higher in each group of workers than in the control group (p < 0.001 for any comparison). Concentrations in the workers varied with the type of job, the highest values being found in workers engaged in the power station, in the two baking impregnation units and in the green electrode unit. CONCLUSIONS: Implementing preventive measures significantly reduced exposure to PAHs at a graphite electrode plant. The reduction in median and peak concentrations of 1-hpur, which reflects total exposure to, and internal dose of PAHs, was most evident in workers employed in the units where preventive measures had been taken. Despite an overall reduction, further preventive measures are needed to minimise exposure to PAHs and consequently the risk of adverse health effects.

Biomarkers↗

PubMedDate not supplied

Comparison of an indirect format ELISA on modified graphite and polystyrene surfaces against triazines.

An indirect format enzyme-linked immuno-sorbent assay (ELISA) on graphite rods ( 0.8 mm x 20 mm) and, for comparison, on microtiter plates has been developed against terbuthylazine. For this purpose, a series of 2-aminoalkyl-4-chloro-6-terbuthyl-s-triazine-2,6-diamine ELISA haptens with alkyl spacer lengths of 2, 4, 6, and 8 CH2 groups has been synthesized. The graphite rods or the microtiter plates were covered by a polymerized glutaraldehyde network, and the ELISA haptens have been coupled by imino coupling to the free aldehyde groups of that network. epsilon-Aminocaproic acid has been used as an agent to block unspecific binding sites. The ELISA was run in a competitive mode, where the immobilized ELISA hapten and the solute terbuthylazine as a target analyte compete for the solute antibody.

Enzyme-Linked Immunosorbent Assay↗

PubMed2001

Determination of beryllium and selenium in human urine and of selenium in human serum by graphite-furnace atomic absorption spectrophotometry.

For human urine beryllium (Be), each sample (500 microl) was diluted (1+1) with Nash reagent (containing 0.2% (v/v) acetylacetone and 2.0 M ammonium acetate buffer at pH 6.0) and then a 20-microl volume of Triton X-100 (0.4%, v/v) aqueous solution was added. An aliquot (10 microl) of the diluted urine mixture was introduced into a graphite cuvette and was atomized according to a temperature program. The method detection limit (MDL, 3sigma) for Be was 0.37 microg/l in the undiluted urine sample and the calibration graph was linear up to 65.0 microg/l. Calibration graphs were prepared by the standard addition method. Accuracies of 98.6-102% were obtained when testing standard reference material (SRM 2670) freeze dried human urine samples. Precision (relative standard deviation, RSD) for urine Be was < or = 2.3% (withinrun, n = 5) and was < or = 3.0% (between-run, n = 3). For human urine and serum selenium (Se), samples (100 microl) were diluted with HNO3 (0.2%, v/v) to make a (1+1) dilution for urine analysis or a (1+4) dilution for serum analysis. An additional aliquot (10 microl) of Triton X-100 (0.1%, v/v) was added to each 200 microl of (1+1) diluted urine (or 20 microl of the Triton X-100 was added to each 500 microl of (1+4) diluted serum) sample. After the diluted sample mixture (10 microl) was introduced into a graphite cuvette, the corresponding chemical modifier (10 microl, containing Ni2+ + Pd + NH4NO3 in HNO3 (0.2%, v/v)) was added to it and the mixture was atomized. The MDL (3sigma) for Se in urine and in serum was 4.4 and 21.4 microg/l in undiluted sample, respectively, and the calibration graphs were linear up to 150 and 400 microg/l. Accuracies of urine Se were 98.9 - 99.4% by testing SRM 2670 (NIST) urine standards with RSD (between-run, n = 3) within 2.9%; and that of serum Se was 97.2% when testing a certified second-generation human serum (No. 29, #664) with RSD (between-run, n = 3) of 1.4%. The proposed method can be applied easily, directly, and accurately to the measurement of Be and Se in real samples (including six urine Se and four serum Se from patients of Blackfoot Disease in Taiwan).

Beryllium↗

PubMed2002

[Determination of trace palladium in medicament by electric-heated AAS with molybdenum-coated graphite tube].

This paper reports a new method for the determination of palladium in exported medicament doxycycline hydrochloride by graphite furnace atomic absorption spectrometry. The optimum conditions for the determination of trace Pd were investigated in details. When the graphite tube was coated with molybdenum, the sensitivity was enhanced and when EDTA was used as the matrix modifier the matrix interference was eliminated efficiently. The result indicates that the detection limit for Pd is 4.6 x 10(-10) g and the relative standard deviation is 4.3%. The method is accurate and rapid and can be used successfully to determine actual samples. The recovery rate of palladium is in the range of 97.1% to 103.3%.

Doxycycline↗

PubMed2002

[Direct determination of Cu and Pb in edible L-lysine by graphite furnace atomic absorption spectrometry].

The determination of Cu and Pb in edible L-lysine by rapid graphite furnace atomic absorption spectrometry (GFAAS) is described in this paper. The sample is dissolved with thin acid and mensurated directly by GFAAS. It does not need dry ashing and wet digesting and without chemical matrix modifier. The Graphite Furnace's function of pre-treatment is fully used. Results can be obtained as soon as possible and avoid unnecessary contamination and loss of samples. The method is simple, rapid, practical and have good precision and accurate. Under the optimum conditions the result indicates that the relative standard deviation of Cu and Pb is 4.8% and 5.3% respectively, the recovery rate is 100%-110% and 102%-105% separately.

Copper↗

PubMed2003

[Determination of Pb in import ginseng by microwave-digestion graphite-furnace atomic absorption spectrometry].

The determination of lead in import ginseng was studied, where microwave assimilation offers a quick, safe and accurate approach with little pollution compared to conventional methods. In the measurements graphite-furnace atomic absorption spectrometry (GFAAS) was used with the advantages of high sensitivity, high speed and little wastage. The microwave assimilation was programed, the mixed acid was analyzed, the problem of the effect of final assimilating liquid on the inspection results was solved, and the inspection conditions of GFAAS were studied. Based on the many experimental results, the suitable incinerating temperature and atomizing temperature were chosen, and the final graphite-furnace temperature-rising program was determined. This method shows a linear range of 0-100 micrograms.L-1, a determination limit of 2.80 micrograms.L-1, a relative standard deviation of 0.91% and a recovery of 98.13%. The precision and accuracy are satisfying.

Drug Contamination↗

PubMed2004

[Determination of platinum in membrane electrode assembly (MEA) by graphite furnace atomic absorption spectrometry].

The contents of platinum in Membrane Electrode Assembly (MEA) is very important to the cost of proton exchange membrane fuel cell. In this paper, the contents of platinum in MEA were determined by graphite furnace atomic absorption spectrometry. The influences of the program for graphite furnace and the optimum conditum of experiment were systematically studied. The method is simple, rapid, accurate and practical. The result indicates that the relative standard deviation of Pt determination is less than 2.67%. The rate of recovery is 97.3%-101.2%.

Electrodes↗

PubMed1998

[Method for determination research of trace germanium in the serum of cancer patients by graphite furnace atomic absorption spectrometry].

Using a tungstate-coated graphite tube, trace germanium in serum samples was determined by Zeeman graphite AAS with NH4NO3 as a matrix modifier. The sensitivity of Ge can be significantly improved. The matrix interference has been removed. The relative standard deviation is less than 3.61%. The method is simple, rapid and accurate.

Blood Chemical Analysis↗

PubMed1998

[GFAAS determination of trace manganese in human hair with graphite probe furnace].

In this paper, direct determination of trace manganese is reported with graphite probe furnace atomic absorption spectrometry. It is shown that graphite probe furnace system has advantages in terms of accuracy, sensitivity, speed, simplicity. The proposed method has been applied to the determination of trace manganese in human hair with satisfactory results.

Graphite↗

PubMed1999

[Determination of trace arsenic using GFAAS with metal-coated graphite tube].

The sensitivity, precision and disturbance-resisting property were studied by using metal-coated graphite tube for electrically heated atomic absorption spectrometry. The surface characteristic of the metal-coated graphite tube was studied by using X-ray diffraction meter and scanning electron microscope. The mechanism of satisfactory performance was discussed.

Arsenic↗