Graphite Tube Research Articles

Methods for vanadium determination in fuel oil by GF AAS with microemulsification and acid digestion sampling

Two methods for vanadium determination in fuel oil are proposed using GF AAS. The first is based on the preparation of a microemulsion followed by direct injection into the graphite tube. The pyrolysis and atomization temperatures, 1500 and 2700 ºC, respectively, were chosen from the temperature curves. This procedure allows determination of vanadium with a detection limit of 0.10 µg g-1 and characteristic mass of 87 pg. The other method uses total acid digestion of the sample with sulfuric acid, nitric acid and hydrogen peroxide. In this procedure, the pyrolysis and atomization temperatures recommended were 1000 and 2700 ºC, respectively. Among the analytical characteristics for this method are a detection limit of 0.25 µg g-1 and a characteristic mass of 63 pg. The accuracy of both procedures was confirmed by the determination of vanadium in the certified reference material NIST SRM 1634c-trace metals in fuel oil.

Effect of wear of the atomic-absorption spectrometer graphite furnace on the analytical zone temperature

One mechanism of increase in the heating temperature of the analytical zone of the graphite tube furnace of the atomic-absorption spectrometer as a result of wear is discussed. The influence of the furnace profile on its heating temperature is shown, and the calculated heating temperature of the standard tube is compared to the temperature in the special case where the cross-section area of the analytical zone of the furnace is reduced by half. Experimental proofs of a given temperature excess, as well as of a relation between the change in the tube profile and the decrease in its mass, are given. The dependence of temperature on the furnace mass and the number of measurements has been investigated. The necessity of taking into account the increase in the heating temperature of the furnace in the wear process has been considered.

Determination of natural Sr and 90Sr in environmental samples by ETV-ICP-MS

The determination of Sr in environmental samples by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) is described. Two ETV devices, a commercially available HGA-600MS graphite tube unit and a home-made W-coil, were examined in combination with DRC technology to remove isobaric interferences when measuring 90Sr. Best results were obtained using the HGA-600MS device. Interferences from Y and Zr could be removed when these elements were present at concentrations up to 1 and 100 mg kg−1, respectively, an improvement of 15 and 30-fold over solution nebulization. Temporal separation of analyte and isobaric interferents makes possible the use of simplified sample preparation procedures, substantially increasing sample throughout and reducing the chances of analyte loss or contamination. For the graphite-based HGA system, procedural LODs of 3.5 pg g−1 could be obtained with precision better than 7% at 350 pg g−1. The accuracy of the method was validated by determination of natural Sr in NRC CRM MESS-3 (Marine Sediment), LUTS-1 (Non Defatted Lobster Hepatopancreas), PACS-2 (Marine Sediment) and SLRS-4 (Riverine Water) and by recovery of 90Sr spikes added to these matrices.

Determination of trace impurities in titanium dioxide by direct solid sampling electrothermal atomic absorption spectrometry

A true direct solid sampling electrothermal atomic absorption spectrometry method with Zeeman-effect background correction (Analytik Jena ZEEnit 60 AAS) was developed for the determination of As, Cd, Hg, Pb, Sb and Zn in powdered titanium dioxide of pharmaceutical, food and cosmetics grade. The interaction of the titanium matrix and graphite surface of the sample carrier boat in a transversely heated graphite tube atomizer was investigated. Conversion of titanium dioxide to interfering TiO 2–TiC-liquid phase, running out the sampling boat, was observed at temperatures above 2000 °C. The temperature program was optimized accordingly for these volatile analytes in atomization and cleaning steps in order to prevent this interference and to prolong significantly the analytical lifetime of the boat to more than one thousand runs. For all elements, calibration by aqueous standard addition method, by wet-chemically analyzed samples with different content of analytes and/or by dosing one sample in different amounts, were proved as adequate quantification procedures. Linear dynamic calibration working ranges can be considerably expanded up to two orders of magnitude within one measurement run by applying three-field dynamic mode of the Zeeman background correction system. The results obtained by true direct solid sampling technique are compared with those of other independent, mostly wet-chemical methods. Very low limits of detection (3 σ criterion) of true solid sampling technique of 21, 0.27, 24, 3.9, 6.3 and 0.9 ng g − 1 were achieved for As, Cd, Hg, Pb, Sb and Zn, respectively.

One-dimensional diffusion model in an inhomogeneous region

A one-dimensional model is developed to describe atomic diffusion in a graphite tube atomizer for electrothermal atomic adsorption spectrometry. The underlying idea of the model is the solution of an inhomogeneous one-dimensional diffusion equation, with the diffusion coefficient being a function of temperature over the entire inhomogeneous region. An analytical solution of the problem is obtained in the form of a Green’s function.

Neutron Activation Analysis, Atomic Absorption and X‐Ray Fluorescence Spectrometry Review for 2004–2005

These technologically mature techniques occupied a stable to modestly increasing sector of the spectrum of analytical methods in Earth and environmental sciences in 2004–5. Despite this, several notable advances were reported in this two year period. In the field of X‐ray fluorescence spectrometry, these included the development of portable synchrotron and total reflection instruments, the use of pyroelectric crystals as X‐ray generators, introduction of high‐purity Ge detector arrays, and the development of an XRF imaging spectrometer with the capability of mapping analytes and X‐ray intensity ratio. Atomic absorption s spectrometry saw major work published on high‐resolution continuum source AAS (HR‐CS AAS) involving the development of a xenon short‐arc lamp. Other advances included the use of laser wave mixing in a graphite furnace tube (with a claimed detection limit of 10–16 g g‐1), solid sampling and ultrasound in sample preparation. Neutron activation analysis saw two innovations that may herald future growth in this technique, namely a neutron source free of a nuclear reactor and a detector operating at room temperature.

Flow injection on-line dilution for zinc determination in human saliva with electrothermal atomic absorption spectrometry detection

An automated method is described for the determination of zinc in human saliva by electrothermal atomic absorption spectrometry (ET AAS) after on-line dilution of samples with a significant reduction of sample consumption per analysis (<0.4 mL including the dead volume of the system). In order to fulfill this aim without changing the sample transport conduits during the experiments, a flow injection (FI) dilution system was constructed. Its principal parts are: one propulsion device (peristaltic pump, PP) for either samples, standards or washing solution all located in an autosampler tray and for the surfactant solution (Triton X-100) used as diluent, and a two-position time based solenoid injector (TBSI 1) which allowed the introduction of 10 μL of either solution in the diluent stream. To avoid unnecessary waste of samples, the TBSI 1 also permitted the recirculation of the solutions to their respective autosampler cups. The downstream diluted solution fills a home made sampling arm assembly. The sequential deposition of 20 μL aliquots of samples or standards on the graphite tube platform was carried out by air displacement with a similar time based solenoid injector (TBSI 2). The dilution procedure and the injection of solutions into the atomizer are computer controlled and synchronized with the operation of the temperature program. Samples or standards solutions were submitted to two drying steps (at 90 and 130 °C), followed by pyrolysis and atomization at 700 and 1700 °C, respectively. The aqueous calibration was linear up to 120.0 μg L −1 for diluted standard solutions/samples and its slope was similar ( p > 0.05) to the standard addition curve, indicating lack of matrix effect. The precision tested by repeated analysis of real saliva samples was less than 3% and the detection limit (3 σ) was of 0.35 μg L −1. To test the accuracy of the proposed procedure, recovery tests were performed, obtaining mean recovery of added zinc of 97.8 ± 1.3%. Furthermore, Zn values estimated by the procedure developed in this work were compared with those obtained by a standard addition flame-AAS method applied to 20 randomly selected saliva samples. No significant differences ( p > 0.05) were obtained between the two methods. Zinc levels in saliva samples from 44 healthy volunteers, 15 male and 29 female, with ages between 20 and 51 years (mean 30.50 ± 9.14 years) were in the range 22–98 μg L −1 (mean of 55 ± 17 μg L −1), similar to some and different from others reported in the literature. It was found that zinc values for male were statistically higher ( p = 0.006) than for female.

Determination of Hg and Se in biological materials by chemical vapor generation electrothermal vaporization inductively coupled plasma mass spectrometry using isotope dilution calibration after microwave-assisted digestion with Aqua Regia

A method for the determination of Hg and Se in biological materials by chemical vapor generation electrothermal vaporization inductively coupled plasma mass spectrometry (CVG-ETV-ICP-MS) using isotope dilution calibration after acid digestion is proposed. The samples were digested with aqua regia in a microwave oven. The isotope ratios used for quantification were: 201Hg/202Hg and 77Se/82Se. A NaBH4 solution stabilized with NaOH was used as reducing agent. The retention and vaporization temperatures in the graphite tube were 150 and 2000 oC, respectively. Six certified biological materials were analyzed and the obtained concentrations were in good agreement with the certified values according to the t-test for a confidence level of 95%. The detection limits in the sample were 0.7 and 3 ng g-1, for Hg and Se respectively. The method is precise, accurate and adequate for the analysis of biological samples in routine and demonstrates the feasibility of using isotope dilution for the proposed system.

Deactivation of singlet oxygen by single-wall carbon nanohorns

Abstract The deactivation rate constant of singlet oxygen 1O2 by single-wall carbon nanohorns (SWNHs) was determined. The estimated rate constant by SWNHs, 8 × 104 L g−1 s−1, was significantly larger than the physical quenching rate constant by α-Tocopherol, 0.9 × 104 L g−1 s−1. The origin of this remarkable efficiency of SWNHs for 1O2 deactivation is ascribed to the unique curvature of the graphitic tube in their horn shaped structure.

Feasibility of using solid sampling graphite furnace atomic absorption spectrometry for speciation analysis of volatile and non-volatile compounds of nickel and vanadium in crude oil

A method for the direct determination of volatile and non-volatile nickel and vanadium compounds in crude oil without previous treatment using direct solid sampling graphite furnace atomic absorption spectrometry is proposed. The crude oil samples were weighed directly onto solid sampling platforms using a microbalance and introduced into a transversely heated solid sampling graphite tube. In previous work of our group losses of volatile nickel and vanadium compounds have been detected, whereas other nickel and vanadium compounds were thermally stable up to 1300 and 1600 °C, respectively. In order to avoid this problem different chemical modifiers (conventional and permanent) have been investigated. With 400 μg of iridium as permanent modifier, the signal started to drop already after two atomization cycles, possibly because of an interaction of nickel (which is a catalyst poison) with iridium. Twenty micrograms of palladium applied in each determination was found to be optimum for both elements. The palladium was deposited on the platform and submitted to a drying step at 150 °C for 75 s. After that the sample was added onto the platform and submitted to the furnace program. The influence of sample mass on the linearity of the response and on potential measurement errors was also investigated using four samples with different nickel content. For the sample with the lowest nickel concentration the relationship between mass and integrated absorbance was found to be non-linear when a high sample mass was introduced. It was suspected that the modifier had not covered the entire platform surface, which resulted in analyte losses. This problem could be avoided by using 40 μL of 0.5 g L −1 Pd with 0.05% Triton X-100. Calibration curves were established with and without modifier, with aqueous standards, oil-in-water emulsions and the certified reference material NIST SRM 1634c (trace metals in residual fuel oil). The sensitivity for aqueous standards and emulsions was close to that for SRM 1634c, making possible the use of aqueous standards for calibration. The limits of detection and quantification obtained for nickel and vanadium under this condition were found to be 0.02 and 0.06 μg g −1, respectively, for both elements, based on 10 mg of sample. Nickel and vanadium were determined in the samples with (total Ni and V) and without the use of Pd (thermally stable compounds), and the concentration of volatile compounds was calculated by difference. The results were compared with those obtained by high-resolution continuum source graphite furnace atomic absorption spectrometry by emulsion technique; no significant differences were found for total Ni and V at the 95% confidence level according to a Student's t-test.

Comparison of different permanent chemical modifiers for lead determination in Orujo spirits by electrothermal atomic absorption spectrometry

Different analytical methods for the determination of lead in Orujo spirits by electrothermal atomic absorption spectrometry (ETAAS) were developed using permanent modifiers (W, Ir, Ru, W-Ir and W-Ru) thermally deposited on platforms inserted in pyrolitic graphite tubes and Pd–Mg(NO 3) 2 conventional modifier mixture. In all cases, the Pb determination was performed without any sample pretreatment or preconcentration steps. The comparison between the chemical modifiers employed has been made in terms of pyrolysis and atomization temperatures, characteristic masses, detection limits, and atomization and background signal shapes. The limits of detection obtained were 0.375, 0.387, 0.109, 0.251 and 0.267 ng mL −1 for W, Ir, Ru, W–Ir and W–Ru, respectively and 0.710 ng mL −1 for Pd–Mg(NO 3) 2. The characteristic masses were 14.1, 11.2, 5.6, 8.3 and 9.3 pg for W, Ir, Ru, W–Ir and W–Ru, respectively and 22.2 pg for Pd–Mg(NO 3) 2. For all the developed procedures using the different modification systems, the relative standard deviations (<10%) and the analytical recoveries (95–103%) were acceptable. The more suitable methods for Pb determination in distillate spirits were those using permanent modifiers in contrast with classical Pd–Mg(NO 3) 2. The best analytical performance was achieved for W, Ir and W–Ir methods, which were applied to lead determination in Orujo spirit samples from Galicia (NW Spain). The Pb concentrations found in the analyzed samples were comprised in the range (<LOD to 1.5 μg mL −1).

Octadecyl immobilized silica beads packed microcolumn versus PTFE knotted reactor as Cd(OH) 2 precipitate collection media coupled to ETAAS for cadmium determination

Octadecyl immobilized surface was proved to function as an effective medium for collecting cadmium hydroxide precipitate. A thorough comparison of precipitate collection and related analytical performances was made using a C18 microcolumn packed into a lab-on-valve system and a polytetrafluoroethylene knotted reactor (PTFE-KR) as the precipitate collection medium. Cadmium was isolated as hydroxide precipitate and collected onto the surface of the C18 microcolumn or the inner surface of the PTFE-KR. The precipitate was then quantitatively eluted with 20 μl nitric acid (1%), and the eluate was subsequently transported into the graphite tube of the ETAAS instrument for atomization. With a sampling volume of 600 μl, the detection limits (ng 1-1), enrichment factors, retention efficiencies (%), precisions (%, 0.05 ng 1-1), and sampling frequencies by using a C18 microcolumn/PTFE-KR were 1.7/3, 28/14, 93/48, 2.1/4.7, and 13/20, respectively. The procedure was validated by analyzing the cadmium contents in three certified references materials: river sediment (CRM 320), sea lettuce (CRM 279), and frozen cattle blood (GBW 09140). The results obtained were in good agreement with the certified values.

Determination of copper and nickel in vegetable oils by direct sampling graphite furnace atomic absorption spectrometry

The quality of food products has been receiving great attention due to its influence on human nutrition and health. In this sense, the determination of trace metals in foods has turned an important field on food analysis. Concerning vegetable oils, its metal trace composition is an important criterion for the assessment of their quality once it is known that trace metals affect their rate of oxidation, influencing freshness, keeping properties as well as storage. In the present work an analytical method which enables the direct determination of Cu and Ni in vegetable oils by graphite furnace atomic absorption spectrometry (GFAAS), using a “solid” sample strategy is presented: in nature, samples are directly weighed on the graphite platform boat and inserted in the graphite tube. An adequate temperature program permitted the calibration by external aqueous analytical curves. Good concordance between the proposed procedure and EPA procedures was found in the analysis of real samples. Limits of detection of 0.001 and 0.002 μg g −1 were found for Cu and Ni, respectively, in the original samples, and they were comfortably below the concentrations found.

Lead ultra-trace on-line preconcentration and determination using selective solid phase extraction and electrothermal atomic absorption spectrometry: applications in seawaters and biological samples

In this work, a new chelating resin [1,5-bis (2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide immobilised on aminopropyl-controlled pore glass (550 A; PSTH-cpg) was synthesised and packed in a microcolumn which replaced the sample tip of the autosampler arm. The system was applied to the preconcentration of lead. When microliters of 10% HNO3, which acts as elution agent, pass through the microcolumn, the preconcentrated Pb(II) is eluted and directly deposited in a tungsten-rhodium coated graphite tube. With the use of the separation and preconcentration step and the permanent modifiers, the analytical characteristics of the technique were improved. The proposed method has a linear calibration range from 0.012 to 10 ng ml(-1) of lead. At a sample frequency of 36 h(-1) with a 90 s preconcentration time, the enrichment factor was 20.5, the detection and determination limits were 0.012 and 0.14 ng ml(-1), respectively and the precision, expressed as relative standard deviation, was 3.2% (at 1 ng ml(-1)). Results from the determination of Pb in biological certified reference materials were in agreement with the certified values. Seawaters and other biological samples were analysed too.

Zirconia‐coated graphite adsorption bar micro‐extraction combined with ETV‐ICP‐MS for the determination of trace amounts of Cd, Hg and Pb in environmental and biological samples

In this work, a new and simple micro-extraction method termed graphite adsorption bar micro-extraction was developed, for the first time, for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) determination of trace Cd, Hg and Pb. In this method, the graphite bar was first coated with zirconia and then inserted into the sample solution for extraction. The graphite bar enriched with the analytes was inserted directly into a graphite tube, and subsequently analyzed by ETV-ICP-MS according to an established temperature program. The experimental parameters, which had influence on the extraction and vaporization, were systematically investigated and the optimal experimental conditions were established. Under the optimized conditions, the detection limits of the method were 0.05, 0.42 and 0.06 pg/ml for Cd, Hg and Pb and the relative standard deviations (RSDs) for 11 replicates at the 0.1 ng/ml level were 7.4, 8.2 and 7.7%, respectively. The proposed method was successfully applied to the determination of trace Cd, Hg and Pb in environmental and biological samples. The results of the experiments indicate that the method has a high enrichment factor and sample utilization efficiency. Furthermore, the method is fast and environment-friendly.

High performance liquid chromatography hydride generation in situ trapping graphite furnace atomic absorption spectrometry: A new way of performing speciation analysis using GFAAS as detector

A new procedure for the speciation analysis of hydride forming elements using GFAAS as detector is proposed. The separation of the species is performed by HPLC and the eluent flow is merged with HCl and NaBH 4 solutions moved by peristaltic pumps controlled by a flow injection apparatus. As the species emerges from the column, its respective hydride is formed and carried through the autosampler capillary to an Ir treated graphite tube pre-heated at 300 °C, where it is trapped. After the hydride collection, the autosampler arm is moved from the tube and atomization takes place. The sequence is repeated for the next emerging species. The feasibility of the system was evaluated for the speciation of As (III) and As (V) in waste water samples. The retention times were previously determined using a more concentrated mixed analytical solution and a quartz tube as atomizer. The analytical curves obtained by the proposed procedure showed similar slopes for both species as well as coefficient of regression better than 0.99. Limits of detection were 0.2 ng/mL for both species, 50 times better then the same assembly using a quartz tube atomizer. In the analysis of certified reference materials the sum of the As (III) and As (V) species concentrations were in close agreement with the arsenic concentration certified for total arsenic.

Analytical performance of ETAAS method for Cd, Co, Cr and Pb determination in blood fractions samples

An electrothermal atomic absorption method (ETAAS) for direct determination of several toxic trace elements (Cd, Co, Cr, Pb) in human blood fractions was developed, because of increasing interest of toxic elements distribution in various blood constituents. Zeeman background correction and pyrolitically coated graphite tubes with L’vov platforms were used. Centrifugation was employed for the separation of blood fractions at different centrifugal conditions at 1200 × g and 3000 × g. The samples were acid-digested by HNO 3 in closed tubes under high temperature and pressure before injection into graphite furnace. Two common modifiers were used and were compared for their effectiveness to the determination of each analyte at the examined blood fractions. The effect of modifier, matrix, calibration technique and peak characteristic (peak area and peak height) on the total variation of the method was examined by analysis of variance. The sensitivity and recovery (Cd 98–110%, Cr 93–109%, Co 95–106% and Pb 91–107%) of the developed method are presented for the various fractions. The overall precision (R.S.D.) using peak area (Cd 6.3–13.1%, Cr 8.2–13.9%, Co 7.4–8.5% and Pb 7.0–11.8%) and peak height measurements (Cd 1.1–9.3%, Cr 6.5–13.5%, Co 6.5–17.3% and Pb 6.9–14.8%) are also presented for pellet and supernatant solution. Standard addition technique was more accurate in terms of analyte recovery.

On-line cloud point extraction combined with electrothermal vaporization inductively coupled plasma atomic emission spectrometry for the speciation of inorganic antimony in environmental and biological samples

A new method for the determination of inorganic Sb species by on-line cloud point extraction combined with electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) is presented and evaluated. The method is based on the complexation of Sb(III) with pyrrolidine dithiocarbamate (PDC) which form an hydrophobic complex at pH 5.5 and subsequently enter surfactant-rich phase at pH 5.5, whereas Sb(V) remained in aqueous solutions. The preconcentration step is mediated by micelles of the non-ionic surfactant Triton X-114 with ammonium pyrrolidine dithiocarbamate (APDC). The micellar system containing the complex was loaded into the FIA manifold at a flow rate of 2.5 mL min −1, and the surfactant-rich phase was retained in a microcolumn packed with absorbent cotton, at pH 5.5. After the surfactant-rich phase was eluted with 100 μL acetonitrile, it was determined by ETV-ICP-AES. Sb(V) is reduced to Sb(III) by l-cysteine prior to determined total Sb, and its assay is based on subtracting Sb(III) from total antimony. The main factors affecting separation/preconcentration and the vaporization behavior of analyte in graphite tube were investigated in detail. Under the optimized conditions, the precision relative standard deviation (R.S.D.) for eight replicate measurements of 0.2 μg mL −1 Sb(III) was 4.3%. The apparent concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for ETV-ICP-AES detection and in the initial solution, was 872 for Sb(III). The limit of detection (LOD) for Sb(III) was 0.09 μg L −1. The proposed method was successfully applied for the speciation of inorganic antimony in different water samples and urine sample with satisfactory results.

Minimization of sample pretreatment for Al, Cu and Fe determination in coconut water by electrothermal atomic absorption spectrometry

Fast and reliable methods for the direct determination of Al, Cu and Fe in unprocessed coconut water by electrothermal atomic absorption spectrometry are proposed. For Fe determination, 100 µL of sample were diluted with 1400 µL of 0.1% v/v HNO3. Aliquots of 10 µL of this solution were injected into the graphite tube without any chemical modifier. For Al and Cu determinations, samples were slightly diluted (1250 µL of sample + 250 µL of 0.6% v/v HNO3 + 0.6% m/v Triton X-100) directly into the auto sampler cups. In this case, aliquots of 10 µL of an oxidant mixture (15% v/v H2O2 + 1.0% v/v HNO3) were co-injected with 15 µL of samples or analytical solutions into the graphite tube. The oxidant mixture minimized the carbonaceous residues formation and increased graphite tube lifetime in 75%, allowing up to 200 heating cycles. The detection limits and characteristic masses were 1.0 mg L-1 and 30 pg for Al, 0.7 µg L-1 and 20 pg for Cu, and 2.0 µg L-1 and 10 pg for Fe, respectively. The reliability of the proposed methods was evaluated by addition and recovery tests (104 ± 1% for Al, 98 ± 3% for Cu, and 97 ± 1% for Fe).

Properties of&lt;tex&gt;$rm MgB_2$&lt;/tex&gt;Superconductor by Doping Impurity of SiC, Graphite,&lt;tex&gt;$rm C_60$&lt;/tex&gt;, and C Nano-Tube

Since MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconductor was discovered by Akimitsu, many scientists has been studied this new intermediate temperature superconductor material. Recently Dou reported the critical current density and flux pinning of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is enhanced by doping of SiC nano powder, and Fujii reported MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconductor made by the powder-in-tube in-situ process using MgH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as a precursor powder enhanced the critical current density especially under high magnetic field. Also Matsumoto reported the irreversibility field of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> tape prepared by the in-situ powder in tube process using MgH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as a precursor powder increased to 23 T by the SiC doping. These results show MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has high potential as a strong candidate for a practical use. We study the effects of doping nano carbon impurity because graphite has the same structure as the hexagonal Boron structure in MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . We added carbon impurities of graphite, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> , and open-ended carbon nano tube respectively to MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> conductors made by powder in tube ex-situ process