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At least 361 records · Page 20Linked to original sources

PubMed2006

[Determination of lead in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction with dithizone].

Cloud point extraction was used for the preconcentration of lead after the formation of a complex with dithizone in the presence of surfactant Triton X-114, and then the lead was determined by graphite furnace atomic absorption spectrometry. The conditions affecting the separation and detection process were optimized. Separation of the two phases was accomplished by centrifugation for 15 min at 4 000 rpm. Upon cooling in an ice-bath, the surfactant-rich phase became viscous. The aqueous phase could then be separated by inverting the tubes. Later, a solution of methanol containing 0.1 mol x L(-1) of HNO3 was added to the surfactant-rich phase up to 0.5 mL. The samples were determined by graphite furnace atomic absorption spectrometry with NH4H2PO4 and Mg(NO3)2 as a chemical modifier. At pH 8.0, the preconcentration of only 10 mL sample in the presence of 0.05% Triton X-114 and 20 micromol x L(-1) dithizone permitted the detection of 0.089 microg x L(-1) lead. The enhancement factors were 19.1 times for lead. The calibration graph using the preconcentration system for lead was linear with a correlation coefficient of 0.998 from levels near the detection limits up to at least 30 microg x L(-1). The regression equation was A = 0.026 1c (microg x L(-1)) + 0.010 6. The proposed method has been applied to the determination of lead in water samples.

Dithizone↗

PubMed1978

Evaluation of polytetrafluoroethylene-graphite-coated total hip prostheses in goats.

This study was designed to determine if a porous polytetrafluoroethylene-graphite coating could furnish long-term stabilization of total hip prostheses. Prostheses were surgically implanted in 12 mature goats, which were observed postoperatively for as long as 1 year. Effective stabilization occurred in only 4 animals. Poor results in the other animals were attributed to lack of stabilization of the prostheses following initial implantation, which allowed movement at the interface between bone and polytetrafluoroethylene-graphite.

Animals↗

PubMed1995

[A case of pulmonary tuberculoma with pneumoconiosis (graphite lung) that appeared to be lung cancer].

We report a rare case of tuberculoma with pneumoconiosis (Graphite lung). A 62-year-old man was admitted to our hospital for diagnosis of a rapidly growing coin lesion in the right lung (S8). He had worked for 42 years in a foundry and given a diagnosis of pneumoconiosis (Graphite lung). Because transbronchial lung biopsy and percutaneous needle aspiration biopsy were not diagnostic, the right lower lobe was partially resected. Histological examination revealed the presence of caseous necrosis in a solitary mass. Therefore, it is important to consider tuberculoma in the differential diagnosis of a coin lesion in patients with pneumoconiosis.

Diagnosis, Differential↗

PubMedDate not supplied

Determination of lead in table wines by graphite furnace atomic absorption spectrometry.

A quick, easy method was developed for the analysis of table wines for lead quantitated at > or = 14 ng Pb/mL wine. The method uses graphite furnace atomic absorption spectrometry with Zeeman background correction and a L'vov pyrolytic graphite platform. Ammonium dihydrogen phosphate is used as a matrix modifier. Wines are diluted by a factor of 10 with 1% HNO3 and analyzed directly. Their absorbances are compared with those of a standard curve prepared with 1% HNO3. Analytical results obtained by comparison with a standard curve agreed with those obtained by the method of standard additions. Four white, 4 red, and 2 rosé wines were studied. Pb concentrations varied from 15 to 135 ng Pb/mL. Wines fortified with 100 ng Pb/mL had an average recovery of 94%. The average short-term relative standard deviation (RSD) was 2.1%; the average long-term RSD was 7.4%. The estimated detection (3 sigma) and quantitation (10 sigma) limits were 4 and 14 ng Pb/mL, respectively.

Lead↗

PubMedDate not supplied

A nitric oxide biosensor based on horseradish peroxidase/kieselguhr co-modified pyrolytic graphite electrode.

A reagentless nitric oxide (NO) biosensor was prepared using a pyrolytic graphite (PG) electrode modified with a composite film containing horseradish peroxidase (HRP) and kieselguhr. Noticeably, the electron-transfer reactivity of HRP was significantly enhanced when incorporated in the inorganic kieselguhr material. Consequently, we observed the direct electrochemical response of HRP in this composite film, which would be otherwise electrochemically silent (in the absence of kieselguhr). Importantly, this modified electrode demonstrated nice catalytic activity, as well as high stability, towards the reduction of NO. The peak current related to NO was linearly proportional to its concentration from 2.0 x 10(-7) to 2.0 x 10(-5) mol/L, and the relative standard deviation was 4 % for five successive determinations at a NO concentration of 1.0 x 10(-5) mol/L. The critical level in concentration was estimated to be (4.0 +/- 0.3) x 10(-8) mol/L.

Biological Assay↗

PubMedDate not supplied

Cathodic electrochemiluminescence of Ru(bpy)(3)(2+)/Nafion coated on graphite oxide electrode in purely aqueous solution.

Two cathodic electrochemiluminescence (ECL) peaks have been obtained at -0.99 and -1.80 V (vs. SCE), respectively, from Ru(bpy)(3)(2+)/Nafion coated onto a graphite oxide electrode in purely aqueous solution under cyclic voltammetric (CV) conditions, without addition of any reducing or oxidative reagents. These two ECL peaks were found to correlate to initial scan direction, pH, and reversal potential. Nafion played an important role in the generation of these two ECL peaks because no cathodic emission was observed in the system without Nafion. It seems that a part of Ru(bpy)(3) (3+) electrogenerated at positive potential can remain in the Nafion, even at negative potentials. It was con fi rmed that Ru(bpy)(+) was formed at -1.80 V by addition of S(2)O(8) (2-). The ECL peak at -0.99 V is attributed to the reaction of Ru(bpy)(3+) and OH(-). The ECL peak at -1.80 V is probably due to the annihilation reaction of Ru(bpy)(3+) and Ru(bpy)(+).

2,2'-Dipyridyl↗

PubMed2003

On-column polymer-imbedded graphite inlet electrode for capillary electrophoresis coupled on-line with flow injection analysis in a poly(dimethylsiloxane) interface.

A method for coupling an electrophoretic driven separation to a liquid flow, using conventional fused-silica capillaries and a soft polymeric interface is presented. A novel design of the electrode providing high voltage to the electrophoretic separation was also developed. The electrode consisted of a conductive polyimide/graphite imbedded coating immobilized onto the capillary electrophoresis (CE) column inlet. This integrated electrode gave the same separation performance as a commonly used platinum electrode. The on-column electrode also showed good electrochemical stability in chronoamperometric experiments. In addition, with this electrode design, the electrode position relative to the inlet end of the CE column will always be constant and well defined. The on-line flow injection analysis (FIA)-CE system was used with electrospray ionization (ESI)-time of flight (TOF)-mass spectrometry detection. The preparation of the PDMS (poly(dimethylsiloxane)) interface for FIA-CE is described in detail and used for initial tests of the on-column polymer-imbedded graphite inlet electrode. In this interface, a pressure-driven liquid flow, a make up CE electrolyte and a CE column inlet meet in a two-level cross (95 microm ID) in the PDMS structure, enabling independent flow characterization.

Dimethylpolysiloxanes↗

PubMed1995

Immobilization of heparin oligosaccharides onto radiofrequency plasma modified pyrolytic carbon-coated graphite.

Heparin oligosaccharides with different anticoagulant activities were prepared and immobilized onto pyrolytic carbon coated graphite (PC) heart valve materials commonly used in mechanical heart valve prostheses. Prior to immobilization, PC surfaces were modified by radiofrequency plasma polymerized N-vinyl-2-pyrrolidone (PPNVP) thin films (approximately 100 nm) and derivatized to provide surface hydroxyl groups. Cleaved, low affinity heparin (C-heparin) with factor Xa inhibition activity of 107 to 130 IU/mg, was prepared by partial deaminative cleavage of commercial crude heparin, and high-affinity heparin (HA-heparin) with factor Xa inhibition activity of 550 to 1000 IU/mg was prepared by fractionation of C-heparin using agarose-ATIII affinity chromatography. C-heparin and HA-heparin were immobilized to surface modified PC by reductive amination. Anticoagulant activity of the heparin immobilized surfaces was determined by chromogenic assay for the inhibition of factor Xa. Highest surface anticoagulant activity was measured on C-heparin immobilized surfaces (64.0 +/- 7.3 mIU/cm2) compared with HA-heparin immobilized surfaces (27.2 +/- 12.2 mIU/cm2), suggesting higher binding of C-heparin than HA-heparin on the modified PC surfaces. Immobilized surfaces were evaluated under dynamic flow conditions, by subjecting samples to shear stress of up to 206 dyn/cm2 in the presence of 5% albumin solution or human plasma. Anticoagulant activity of the immobilized heparin was retained, although reduced, and the modified surfaces showed evidence for protein resistance.

Anticoagulants↗

PubMedDate not supplied

Airway reactivity response to aged carbon-graphite/epoxy composite material smoke.

Exposure of naïve guinea pigs for a total of 30 min to aged smoke from pyrolysis of 5, 10 and 100 g of carbon-graphite/epoxy-advanced composite material (cgeCM) elicited changes in the ventilation and breathing pattern reminiscent of an acute, asthmatic episode. The severity of these responses was dose related. Although breathing pattern changes were not definitive of stimulation by a single type of respiratory irritant, non-dimensional indices derived from breath structure appeared to be characteristic of bronchoconstriction possibly complicated by CO(2)-stimulated ventilation. The highest exposure concentration also elicited convulsions in the animals, which may or may not be related to the airway reactivity (AR) response. Upon treatment with fresh air, breathing returned to normal. However, this recovery was transient with some respiratory parameters returning to abnormal levels, possibly indicating a rebound or delayed component of the response. Filtration of particulate material from the smoke moderated but did not eliminate the AR response. Animals exposed to diluted smoke from the pyrolysis of 2 g of cgeCM showed no remarkable changes in breathing or ventilation, suggesting that there may be a threshold for aged cgeCM smoke-elicited AR response.

Animals↗

PubMed1975

Two-year biocompatibility study of ORNL graphite.

A new grade of graphite-isotropic, fine-grained, and of superior strength-has been produced at the Oak Ridge National Laboratory. The possibility of using this material in orthopedic implants is under study at the University of Illinois. As part of this program, plugs 1/8 in. in diam were inserted in holes drilled in the proximal femur of 2 groups of 8-week old male rabbits. The groups were sacrificed at the end of 1 and 2 years. A single i.m. injection of achromycin was given 2 days prior to sacrifice. Thin sections of the plugs and surrounding tissue were examined by microradiography and optical microscopy (white light, polarizing, and fluorescent). All bone was normal. Minimal evidence of irritation or fibrous encapsulation appeared.

Animals↗

PubMed1994

Cyclic fatigue and fracture in pyrolytic carbon-coated graphite mechanical heart-valve prostheses: role of small cracks in life prediction.

A fracture-mechanics based study has performed to characterize the fracture toughness and rates of cyclic fatigue-crack growth of incipient flaws in prosthetic heart-valve components made of pyrolytic carbon-coated graphite. Such data are required to predict the safe structural lifetime of mechanical heart-valve prostheses using damage-tolerant analysis. Unlike previous studies where fatigue-crack propagation data were obtained using through-thickness, long cracks (approximately 2-20 mm long), growing in conventional (e.g., compact-tension) samples, experiments were performed on physically small cracks (approximately 100-600 microns long), initiated on the surface of the pyrolytic-carbon coating to simulate reality. Small-crack toughness results were found to agree closely with those measured conventionally with long cracks. However, similar to well-known observations in metal fatigue, it was found that based on the usual computations of the applied (far-field) driving force in terms of the maximum stress intensity, Kmax, small fatigue cracks grew at rates that exceeded those of long cracks at the same applied stress intensity, and displayed a negative dependency on Kmax; moreover, they grew at applied stress intensities less than the fatigue threshold value, below which long cracks are presumed dormant. To resolve this apparent discrepancy, it is shown that long and small crack results can be normalized, provided growth rates are characterized in terms of the total (near-tip) stress intensity (incorporating, for example, the effect of residual stress); with this achieved, in principle, either form of data can be used for life prediction of implant devices. Inspection of the long and small crack results reveals extensive scatter inherent in both forms of growth-rate data for the pyrolytic-carbon material.

Graphite↗

PubMed2004

Interference of the electrospray voltage on chromatographic separations using porous graphitic carbon columns.

The electrospray ionization (ESI) voltage is shown to interfere with liquid chromatographic separations performed with packed porous graphitic carbon (PGC) capillary columns. This interference is ascribed to the presence of an electric field over the conductive column in the absence of an earth point between the column and the ESI emitter. The current evolved alters the chromatographic behavior of the catecholamine metabolite 3-O-methyl-DOPA significantly, as both peak splitting and a dramatic decrease in the retention time were observed. Furthermore, the response from the mass spectrometer was decreased by 33% at the same time. A related compound, tyrosine, exhibited decreased retention times but no peak splitting, whereas no shifts in the retention times (or peak splitting) were seen for the less retained dopamine and noradrenaline. When the current through the PGC column was eliminated by the use of an earth point between the column and the ESI emitter, the chromatographic behavior of the column was found to return slowly to normal after hours of equilibration with 60 : 40 (v/v) methanol-ammonium formate buffer of pH 2.9. The behavior of the PGC column with and without the earth point was found to be highly reproducible during a period of 1 month. We propose that the effect of the ESI voltage on the chromatographic behavior of the PGC column is due to associated redox reactions affecting both the PGC particles and the analytes. It is concluded that (for analytical reasons), care should be taken to ensure that no current is flowing through the chromatographic system when interfacing PGC columns, and conducting parts in general, to ESI mass spectrometry.

Chromatography, Liquid↗

PubMed2006

Atmospheric pressure photoionization coupled to porous graphitic carbon liquid chromatography for the analysis of globotriaosylceramides. Application to Fabry disease.

Globotriaosylceramides (Gb(3)) are biological compounds implicated in Fabry disease, a lysosomal storage disease due to the deficient activity of alpha-D-galactosidase A, which results in an accumulation of Gb(3) in many organs. The naturally occurring samples are composed of mixtures of several molecular species differing by the structure of the alkyl chains and the nature of the sphingoid base. Atmospheric pressure photoionization mass spectrometry (APPI-MS) proved to be an efficient method for the analysis of globotriaosylceramide molecular species, both in direct injection and by coupling with liquid chromatography (LC). In the positive ion mode, in-source fragmentations yield very precious information that can be used to determine the structure of the alkyl chains. In the negative ion mode, the chloroform solvent participates to the analyte ionization by forming an adduct with chloride ions generated in situ. Combination of LC on a Porous Graphitic Carbon stationary phase and APPI-MS allowed the detection of a great number of species from biological samples isolated from Fabry patients. This method could be an interesting analytical tool for the biochemical investigation of (sphingo) lipid metabolism.

Biomarkers↗

PubMed2004

Wheat digalactosyldiacylglycerol molecular species profiling using porous graphitic carbon stationary phase.

The potential of porous graphitic carbon stationary phase (PGC) was assessed for the separation of molecular species of digalactosyldiacylglycerol (DGDG). Detection was by an evaporative light scattering detector (ELSD). A conventional optimization strategy allowed definition of a quaternary non-aqueous mobile phase and separation of 9 wheat DGDG molecular species with isocratic elution: methanol/toluene/tetrahydrofuran/chloroform 64.3/21.5/13.7/0.5 v/v with 0.1% of triethylamine and a stoichiometric amount of formic acid. The molecular species were identified by LC/MS. The chromatographic behavior of DGDG on PGC was then compared to previous studies. The addition of a carbon double bond on the alkyl chain decreased the retention. This contribution was less important when the number of unsaturations increased in the alkyl chain. The consequence of this retention behavior with PGC was an elution order of molecular species which did not agree with the partition number as observed with C18 grafted stationary phases.

Chromatography, High Pressure Liquid↗

PubMed2004

Liquid chromatographic analysis of nucleosides and their mono-, di- and triphosphates using porous graphitic carbon stationary phase coupled with electrospray mass spectrometry.

Analysis of nucleosides and nucleotides is desirable in many biological studies, but the task is analytically challenging due to the high polarity of the analytes. In this study, resolution of mixtures containing nucleosides and their mono-, di- and triphosphates was achieved using a porous graphitic carbon (PGC) stationary phase, Hypercarb, under conditions suitable for liquid chromatography/mass spectrometry (LC/MS). Different organic mobile phases and modifiers were evaluated and the separation of 16 nucleosides and nucleotides was optimized using gradient elution with a water/acetonitrile mobile phase containing ammonium acetate and diethylamine as modifiers. The ammonium acetate concentration proved to be critical for retention and diethylamine was found to improve the peak shapes of di- and triphosphates for mass spectrometric detection. A variety of silica-based columns designed for polar compound separation were also tested using optimized LC conditions and compared with results obtained with the Hypercarb column. Only the Hypercarb column provided separations suitable for accurate quantitation of mixed nucleosides and their phosphates.

Chromatography, Liquid↗

PubMed2006

Utility of porous graphitic carbon stationary phase in quantitative liquid chromatography/tandem mass spectrometry bioanalysis: quantitation of diastereomers in plasma.

A major challenge in selecting an appropriate stationary phase for diastereomeric separation is that it is difficult to predict which of the commercially available stationary phases could achieve the required liquid chromatographic (LC) separation. This work describes the selection and evaluation of a porous graphitic carbon (PGC) column coupled with tandem mass spectrometry (MS/MS) for the simultaneous quantitation of an experimental drug candidate (I), its two diastereomeric metabolites (II and III), and its demethylated metabolite (IV) in rat plasma. In addition, we investigated the PGC column for the separation of another drug candidate (VI), its two diastereomeric metabolites (VII and VIII) and its ketone metabolite (IX). The PGC column showed excellent chromatographic resolution for the two diastereomers II and III, as well as for VII and VIII. In contrast, the required resolution for the diastereomers II and III could not be achieved using silica-bonded C(18), C(30), phenyl, perfluorinated, polar embedded and polar end-capped phases. The PGC column showed ruggedness with excellent reproducibility of retention times, peak symmetry and response over a period of more than 400 injections of a plasma acetonitrile-precipitation extract. Excellent accuracy and precision were achieved, with accuracy of 94-108% and intra- and inter-run precision within 9%. This work indicates that PGC is a valuable addition to the repertoire of LC columns used for quantitative LC/MS/MS bioanalysis, especially where the separation and quantitation of diastereomeric analytes is involved.

Animals↗

PubMed1999

The use of a porous graphitic carbon column for desalting hydrophilic peptides prior to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Reversed-phase high-performance liquid chromatography is the standard method for separating peptides generated from proteolytic digests of proteins. Typically, the small hydrophilic peptides from a proteolytic digest are recovered in the flowthrough fraction along with nonvolatile buffers and salts. Unfortunately, the presence of these salts can interfere with subsequent mass spectrometric analysis or Edman sequencing. To overcome this limitation, and thus enable these small peptides to be identified and characterized, we have investigated a porous graphitic carbon (PGC) column for desalting the peptides found in the unretained fraction. Using a volatile mobile phase combined with a PGC column (Hypercarb), we demonstrate that small hydrophilic peptides at the picomole level can be desalted and characterized by matrix-assisted laser desorption and ionization-time-of-flight-mass spectrometry. Even after desalting, we show that the choice of matrix still plays a significant role in distinguishing the small peptides from the matrix background. The utility of this approach is demonstrated with the flowthrough fraction of an endoproteinase Lys-C digest of a recombinant immunoglobulin. In addition, we demonstrate that a PGC column offers an alternative approach for the separation of hydrophilic, phosphorylated peptides from their unphosphorylated counterparts.

Amino Acid Sequence↗

PubMed1995

Surveillance of mortality and cancer incidence among Swedish graphite electrode workers.

Mortality and cancer incidence were investigated among 901 workers at a Swedish company manufacturing graphite electrodes. Current and previous measurements of personal exposure to benzo[a]pyrene were used to calculate individual exposure estimates. Smoking habits were investigated by questionnaire. There were 42 deaths during the study period (1968-1989), whereas 32.3 would be expected, based on age, sex, time, and county-specific population statistics. Three cancers of the respiratory system were found vs 1.2 expected. The overall mortality was slightly elevated, mainly due to an increased number of deaths from external causes. Thus far, no excess risk of cancer has been documented in this cohort. The results indicate that an increased risk of respiratory cancer may be present, but influence from chance cannot be ruled out due to small numbers. The cohort will be under continued surveillance.

Benzo(a)pyrene↗