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PubMedDate not supplied

Magnetic susceptibility effects on 13C MAS NMR spectra of carbon materials and graphite.

13C high-resolution solid-state nuclear magnetic resonance (NMR) was employed to study carbon materials prepared through the thermal decomposition of four different organic precursors (rice hulls, endocarp of babassu coconut, peat, and PVC). For heat treatment temperatures (HTTs) above about 600 C, all materials presented 13C NMR spectra composed of a unique resonance line associated with carbon atoms in aromatic planes. With increasing HTT a continuous broadening of this resonance and a diamagnetic shift in its central frequency were verified for all samples. The evolution of the magnitude and anisotropy of the magnetic susceptibility of the heat-treated carbon samples with HTT explains well these findings. It is shown that these results are better understood when a comparison is made with the features of the 13C NMR spectrum of polycrystalline graphite, for which the magnetic susceptibility effect is also present and is much more pronounced.

Anisotropy↗

PubMed1978

[Biomechanical efficiency and biocompatibility of lubricating sprays PTFE or graphite (author's transl)].

The screws and plates used in operative treatment of fractures cause moments of friction between the bone screw head and the bone plate hole during the tightening of the screws. This results in hidden damage to the grinding metal surfaces, with the danger of erosion corrosion and in a reduction in the screw force. By covering the screw heads with the lubricating sprays PTFE or graphite friction was significantly reduced, the screw force increased by 40% and extensive damage to the surfaces avoided. Lubricating sprays or their extracts, in fetal calf serum or in dimethylsulfoxide, were added to fibroblast cultures. Toxicity was manifest as changes in the synthesis of DNA, as measured by autoradiography. Sprays or spray extracts in fetal calf serum did not inhibit cell proliferation. In vivo experiments in rats reflected the in vitro results, there being no evidence that toxic substances were released from the sprays by physiological solvents: There was a lack of histopathological changes in the inner organs and a local encapsulation of implants which was essentially like that in a teflon control group.

Aerosols↗

PubMed1994

Determinants of urinary thioethers, D-glucaric acid and mutagenicity after exposure to polycyclic aromatic hydrocarbons assessed by air monitoring and measurement of 1-hydroxypyrene in urine: a cross-sectional study in workers of coke and graphite-electrode-producing plants.

A cross-sectional epidemiological study was performed on 286 workers from two coke oven and one graphite electrode plants. The aim was to evaluate the usefulness of monitoring 1-hydroxypyrene (1-HOP) in urine for assessing exposure to polycyclic aromatic hydrocarbons (PAHs), and that of the urinary excretion of thioethers and D-glucaric acid, and the mutagenic activity of urine as indicators or biological effects of PAHs. The results confirm that 1-HOP determination in urine probably reflects exposure to PAHs by all routes and is not significantly influenced by the smoking habit. In comparison with the total PAHs in the air and 1-hydroxypyrene in urine, taken as reference exposure parameters, the results indicate that urinary D-glucaric acid excretion is not positively influenced by PAHs exposure; thioethers determination in urine is of poor value, since the smoking habit is a strong confounding factor. The determination of urinary mutagenicity might contribute to the detection of groups of workers exposed to potentially genotoxic PAHs.

Adult↗

PubMed1996

Determination of selenium in the human brain by graphite furnace atomic absorption spectrometry.

For the investigation of neurological disorders, a development of simple and accessible methods for determining selenium in human brain samples is required. We devised a method of determining selenium using graphite furnace atomic absorption spectrometry (GFAAS). An electrodeless discharge lamp provided the sufficient sensitivity to determine brain selenium. The matrix interferences were avoided by using high temperature, a prolonged pyrolysis step, and a palladium matrix modifier. The technique of standard addition was used to evaluate the sample concentrations. The accuracy of the method was confirmed by a bovine liver reference material. The detection limit of selenium was 0.04 ng. The determined selenium concentrations of human brain cortex and white matter were higher than those of putamen (115-155 and 206-222 ng/g wet wt, respectively). These GFAAS values agreed with those obtained by fluorometric analysis (r = 0.91, n = 10). Moreover, the GFAAS values were compatible to those reported by other researchers (99-274 ng/g wet wt), in which selenium concentrations in putamen also tended to be higher than the other two regions. We conclude that GFAAS is useful for selenium analysis in brain samples.

Brain↗

PubMed1992

Amperometric enzyme sensor for glucose based on graphite paste-modified electrodes.

Amperometric enzyme electrode for glucose is described based on the incorporation of glucose oxidase (GOD) into graphite paste modified with tetracyanoquinodimethane (TCNQ). The incorporated enzyme exhibits high activity and long-term stability over the earlier TCNQ-based glucose sensor (1). The sensor provides a linear response to glucose over a wide concentration range. The response time of the sensor is 15-50 sec, and the detection limit is 0.5 mM. Stable response to the substrate was obtained during a period of 35 d. Application of the sensor in the plasma analysis is reported.

Biosensing Techniques↗

PubMed2002

Biosensors designed for environmental and food quality control based on screen-printed graphite electrodes with different configurations.

Graphite electrodes fabricated by screen-printing have been used as amperometric detectors in biosensors based on NAD(+)-dependent dehydrogenases, tyrosinase, or genetically modified acetylcholinesterases. The mono-enzyme sensors have been optimized as disposable or reusable devices for detection of a variety of substrates important in the food industry ( D-lactic acid, L-lactic acid, acetaldehyde) or in environmental pollution control (phenols and dithiocarbamate, carbamate and organophosphorus pesticides). The sensors were prepared in four configurations differing in enzyme confinement, enzyme immobilization and location of the immobilization agent in the biosensor assembly. Tests on real samples have been performed with the biosensors; D-lactic acid and acetaldehyde have been detected in wine and phenols in air.

Acetaldehyde↗

PubMed2003

Preconcentration of selenium compounds on a porous graphitic carbon column in view of HPLC-ICP-AES speciation analysis.

The retention of organic selenium compounds on a porous graphitic carbon stationary phase was investigated. Different acids were studied as mobile phases to elute selenocystamine, selenoethionine, selenomethionine and selenocystine. Detection was achieved using inductively coupled plasma-atomic emission spectrometry to provide selenium-specific and sensitive detection. The separation of the four species was carried out using methanoic acid. An important on-column preconcentration was obtained when solutes were injected in nitric acid or trifluoroacetic acid (TFA) media. The large injection volume employed (2,500 micro L) allowed us to reach low relative detection limits (2-6 micro g/L). The method, employing TFA as injection solvent and methanoic acid as the eluent was found to be robust with respect to different matrices spiked with selenocompounds.

Buffers↗

PubMed2005

The determination of total Se in urine and serum by graphite furnace atomic absorption spectrometry using Ir as permanent modifier and in situ oxidation for complete trimethylselenonium recovery.

The present work evaluated the use of iridium (Ir) as permanent modifier for the determination of total selenium in urine and serum by graphite furnace atomic absorption spectrometry. Concerning urine, the presence of trimethylselenonium (TMSe(+)) was especially considered. Pyrolysis and atomization temperatures of 1,000 and 2,100 degrees C, respectively, were used. For nondigested urine and serum samples, 0.2% v/v HNO(3) and Triton X-100 were used as diluents, respectively, and the same initial platform Ir treatment was effective for up to 1,100 atomization cycles. Good precision [less than 5% relative standard deviation (RSD)] can be achieved with the proposed method. Low TMSe(+) recovery was observed for nondigested urine samples. Thus, if this species is to be considered in urine analysis, a previous external mineralization step was found to be necessary. Alternatively, an in situ oxidation treatment was developed. Detection limits of 8, 10, and 7 mug l(-1) were obtained after dilution, microwave-assisted digestion, and in situ oxidation procedures, respectively. The accuracy of the method was validated by the analysis of certified reference or commercial quality control materials and spiked samples.

Graphite↗

PubMed2005

Direct determination of selenium in urine samples by electrothermal atomic absorption spectrometry using a Zr plus Rh-treated graphite tube and co-injection of Rh as chemical modifier.

Different chemical modifiers for use with electrothermal atomic absorption spectrometry (ET AAS) were investigated in relation to determining the selenium in human urine samples. The samples were diluted in a solution containing 1% v/v HNO3 and 0.02% m/v cetyltrimethylammonium chloride (CTAC). Studying the modifiers showed that the use of either Ru or Ir as the permanent modifier gave low sensitivity to Se and the peak shape was very noisy, while Zr or Rh gave no peak at all. The same occurred when Zr was used in solution. For mixtures of permanent modifiers, Ir plus Rh or Zr plus Rh gave very low sensitivity, Zr plus Rh with co-injection of Ir in solution was also not efficient, Zr plus Rh in solution gave good sensitivity, but the best results were obtained with a mixture of Zr and Rh as the permanent modifier and co-injection of Rh in solution. Using this last modifier, the following dilutions with the HNO3 and CTAC were studied: 1:1, 1:2, 1:3 and 1:4. The best dilution was 1:1, which promoted good sensitivity and a more defined peak shape and made it possible to correct for the background using a deuterium arc lamp. Under these conditions, a characteristic mass of 26+/-0.2 pg was obtained for Se in aqueous solution. Six certified urine samples were analyzed using matrix matching calibration and the measured concentrations were in agreement with the certified values, according to a t-test at the 95% confidence level. Recovery tests were carried out and the recoveries were in the range 100-103%, with relative standard deviation better than 9%. The limit of detection (LOD, 3 sd, n = 10) was 3.0 microg L(-1) in the sample. The treated graphite tube could be used for at least 600 atomization cycles without significant alteration of the analytical signal.

Electrochemistry↗

PubMed2005

Determination of dopamine in synthetic cerebrospinal fluid by SWV with a graphite-polyurethane composite electrode.

This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite-polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L(-1); pH 7.4). Analytical curves were constructed under optimized conditions (f=60s(-1), DeltaE(a)=50 mV, DeltaE(I)=2 mV) and detection and quantification limits of 6.4x10(-8) mol L(-1) (12.1 microg L(-1)) and 5.2x10(-6) mol L(-1) (0.9 mg L(-1)), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9x10(-6) mol L(-1) dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine.

Dopamine↗

PubMed2005

Determination of oxaliplatin in human plasma and plasma ultrafiltrate by graphite-furnace atomic-absorption spectrometry.

A method for sensitive determination of the anti-cancer agent oxaliplatin in human plasma and human plasma ultrafiltrate (pUF) is presented. The method is based on the quantification of platinum by graphite-furnace atomic-absorption spectrometry, with Zeeman correction and an atomisation temperature of 2,700 degrees C. Sample pretreatment involves dilution of the samples with a solution containing 0.15 mol L(-1) NaCl and 0.20 mol L(-1) HCl in water. Validation was performed in accordance with the most recent FDA guidelines for bioanalytical method validation. All results were within requirements. The validated ranges of quantification were 0.10-400 micromol L(-1) for human pUF and 0.50-400 micromol L(-1) for plasma. The assay is now successfully used to support pharmacokinetic studies of cancer patients treated with oxaliplatin.

Antineoplastic Agents↗

PubMed2005

Investigations into the electrooxidation of guanosine-5'-triphosphate at the pyrolytic graphite electrode.

The electrochemical oxidation of guanosine-5'-triphosphate has been investigated in phosphate-containing electrolytes in the pH range 1.5-10.9 at a pyrolytic graphite electrode by cyclic sweep voltammetry, spectral studies, bulk electrolysis and related techniques. In this pH range, the oxidation occurred in a single well-defined peak (Ia). The peak potential of oxidation peaks (Ep) was found to be dependent on pH, concentration and sweep rate. The kinetics of the UV-absorbing intermediates was followed spectrophotometrically and the decay of the intermediate occurred in a pseudo-first-order reaction. The first-order rate constants for the disappearance of the UV-absorbing intermediate have also been calculated. The products of the electrode reaction were characterized by HPLC and GC/MS. A tentative mechanism for the formation of the products has also been suggested.

Dimerization↗

PubMed1997

Antimony in drinking water, red blood cells, and serum: development of analytical methodology using transversely heated graphite furnace atomization-atomic absorption spectrometry.

An atomic absorption spectrometric (AAS) method has been developed for determining microg/L levels of Sb in samples of water and blood. The AAS method is based on the concept of stabilized temperature platform furnace atomization (STPF) realized through the use of a transversely heated graphite atomizer (THGA) furnace, longitudinal Zeeman-effect background correction, and matrix modification with palladium nitrate-magnesium nitrate-nitric acid. The method of standard additions is not mandatory. The detection limit (3 standard deviations of the blank) is 2.6 microg Sb/L for the water, red blood cells (RBCs), and serum samples. Data are presented on the degree of accuracy and precision. The THGA-AAS method is simple, fast, and contamination-free because the entire operation from sampling to AAS measurement is carried out in the same tube. The method has been applied to the determination of Sb in some leachate tap water samples derived from a static copper plumbing system containing Sn/Sb solders, and in small samples (0.5 ml) of RBCs and serum derived from rats given Sb-supplemented drinking water.

Animals↗

PubMed2005

A molecular-dynamics simulation study of diffusion of a single model carbonic chain on a graphite (001) surface.

Molecular-dynamics simulations have been used to study the diffusion of a short single model carbonic chain on the graphite (001) surface. The calculated diffusion coefficient (D) first increases, then decreases with increasing chain length (N). This abnormal behavior is similar to polymer lateral diffusion at the solid-liquid interface. Furthermore, we have studied the relation between the mean-square gyration radius and N. [Figure: see text].

Carbon↗

PubMed1983

Determination of copper concentration in blood plasma and in ocular and cerebrospinal fluids using graphite furnace atomic absorption spectroscopy.

Published values for the concentration of Cu in cerebrospinal and intraocular fluids cover a very wide range (0.016 to 1.0 microgram/ml) and include values which are several times higher than those which would be consistent with normal physiology. An atomic absorption spectrophotometer equipped with a graphite furnace was used to measure the Cu concentration in these fluids and in blood plasma of toads, rabbits, and cats. Under standard conditions, these fluids yielded high background absorbance and only fractional recovery of added Cu. Parameters were therefore established which eliminated both the high background and the matrix interference and allowed the determination of Cu in 10-microliters aliquots of diluted blood plasma and undiluted cerebrospinal and ocular fluid samples. Under these conditions the Cu measured in the ocular (0.011 to 0.032 microgram/ml) and cerebrospinal fluids (0.033 to 0.050 microgram/ml) of these three species was lower than most previously reported values and only a small fraction (1-3%) of the concentration of Cu in the plasma of the same animals (0.85 to 1.22 micrograms/ml).

Animals↗

PubMed1986

Specific tritium labeling of glucosyl- and galactosylceramides at the 6-position of the carbohydrate moiety using CrO3-graphite.

A new procedure for introducing tritium into the carbohydrate portions of glucosyl- and galactosylceramides was developed using a new catalyst, CrO3-graphite, which specifically oxidizes the primary alcohol group to the aldehyde. About 10% of the glycolipid was converted to the aldehyde and the aldehyde produced was then reduced back to the original form with KB3H4. After methanolysis, more than 96.7% of the radioactivities of [3H]glucosyl- and [3H]galactosylceramides were found to be located in the carbohydrate portions, and the specific activities of the [3H]galactosyl- and [3H]glucosylceramides were 2.08 to 4.30 X 10(4) cpm/nmol, which could be increased greatly by purifying the aldehydes and reducing them with KB3H4. In addition, beta-galactosidase activity was successfully determined with [3H]galactosylceramide as the enzyme substrate; the Km was 18.73 mM and the Vmax was 11.63 nmol/mg/h, indicating that no significant structural modification occurs during the oxidation.

Animals↗

PubMed1981

Determination of copper in urine by graphite furnace atomic absorption spectrometry.

Two methods are described for the determination of copper in urine by graphite furnace atomic absorption spectrometry. The first, suitable for spectrometers capable of making good background correction at 325 nm, involves a direct determination against simple aqueous standards after 2 X dilution of the sample. The second requires no background correction and can be used when background correction is not available or is inadequate. The copper is extracted from the urine with ammonium tetramethylenedithiocarbamate into methylisobutylketone and the extract is analysed for copper. No significant matrix effect was observed for either method. Analysis of random urine samples from 16 normal subjects gave a mean concentration of 0.42 mumol/l with a range of 0.06--1.04 mumol/l.

Copper↗

PubMed1981

The aluminium content of human serum determined by atomic absorption spectroscopy with a graphite furnace.

A method is described for the determination of aluminium in serum by atomic absorption spectroscopy with a graphite furnace. The serum sample is diluted with a diluent of Triton X-100 and HNO3. The dilution enables shorter drying and charring times and a lower charring temperature. The detection limit of the method is 2.5 microgram Al/l serum. Precautions for sample handling are discussed and instrument settings are defined. The direct determination of aluminium in serum is compared with the standard addition method. A good correlation between the two methods was found. Serum from 37 healthy persons was investigated. The serum contained less than 4 microgram Al/l with a range of less than 2.5 microgram to 7 microgram Al/l. The aluminium content of 50 serum samples from hemodialysis patients was determined. The aluminium content of the serum of the hemodialysis patients was in the range of 8 to 713 microgram Al/l. A mean value of 87.7 microgram Al/l (S.D. 122.8) was found.

Aluminum↗