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1.
Prompt-gamma neutron activation (PGNA) analysis is used for the non-invasive measurement of human body composition. Advancements
in portable, compact neutron generator design have made those devices attractive as neutron sources. Two distinct generators
are available: D-D with 2.5 MeV and D-T with 14.2 MeV neutrons. To compare the performance of these two units in our present
PGNA system, we performed Monte Carlo simulations (MCNP-5; Los Alamos National Laboratory) evaluating the nitrogen reactions
produced in tissue-equivalent phantoms and the effects of background interference on the gamma-detectors. Monte Carlo response
curves showed increased gamma production per unit dose when using the D-D generator, suggesting that it is the more suitable
choice for smaller sized subjects. The increased penetration by higher energy neutrons produced by the D-T generator supports
its utility when examining larger, especially obese, subjects. A clinical PGNA analysis design incorporating both neutron
generator options may be the best choice for a system required to measure a wide range of subject phenotypes. 相似文献
2.
K. J. Ellis 《Journal of Radioanalytical and Nuclear Chemistry》2001,248(2):407-412
Prompt-gamma neutron activation (PGNA) is used to measure total-bodynitrogen and hydrogen in humans. Background interference in the gamma spectraarises from both subject and shielding. A Monte Carlo simulation program (MCNP4B2)was used to examine the neutron and gamma signals in the PGNA system ( 241AmBe source). N and H peak regions were assessed in the presenceand absence of calibration phantoms. The simulations suggested extracorporealH peak contributions of up to 30%, depending on subject body habitus. MostN background could be attributed to detector pileup events. The MCNP resultsallowed us to improve shielding design and develop background correction algorithmsto improve measurement precision. 相似文献
3.
R. J. Shypailo B. Workeneh K. J. Ellis 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(1):143-148
Total body nitrogen (TBN) can be used to estimate total body protein, an important body composition component at the molecular level. A system using the associated particle technique in conjunction with prompt gamma neutron activation analysis has been developed for the measurement of TBN in vivo. The system uses a compact D, T neutron generator (~107 n/s) coupled to an internal alpha-particle detector, and a counting system with six bismuth germinate detectors. 14 Subjects were scanned from shoulders to hips (20 min scan time, <0.4 mSv dose) generating complex spectra dominated by signals from C, O, H, and N, with significant peak overlap. Fractional contributions from these elements to regions of interests (ROI) spanning a 4–8 MeV range were determined by algorithms comparing ratios of interrelated ROIs. In addition, multi-component least squares fitting was done to further resolve individual peak activities (MATLAB R2011b). Total body potassium (TBK) was also measured using a whole body gamma counter. Predicted TBN values, based on fat-free mass estimated from TBK, were compared to measured TBN results. Measured versus predicted results for all subjects were not statistically different. Separating subjects by gender also showed no difference between measured and predicted values. The associated particle system showed good agreement with predicted TBN values, but measurement precision was not better than that commonly seen in traditional prompt gamma thermal neutron activation analysis systems. 相似文献
4.
A portable prompt gamma neutron activation (PGNA) spectroscopy system has been developed to analyze the elemental composition (Ca, Si, Al, etc.) of reinforced concrete and to measure chloride contamination. The portable PGNA system consists of a high purity germanium (HPGe) gamma detector with a 70% relative efficiency, a 252Cf neutron source and moderator subsystem, and a portable multichannel analyzer system integrated with a laptop computer. Two types of activation experiments were performed to evaluate the device: first, a detector calibration using a Cl gamma standard provided by a PGNA facility; second, an evaluation of the actual performance of the complete system with the 252Cf source using full scale test slabs containing known amounts of chloride. Both methods indicate that it is feasible to use this device to measure the chloride content of reinforced concrete in the field. The chloride level for the corrosion threshold can be measured with a precision of 10% for a counting time of roughly 6 minutes. This makes the PGNA method competitive with the conventional destructive method. 相似文献
5.
K. J. Ellis S. H. Cohn A. Vaswani I. Zanzi M. Roginsky J. Aloia 《Journal of Radioanalytical and Nuclear Chemistry》1977,37(1):333-343
Total body neutron activation analysis (TBNAA) has used to determine the absolute levels of total body sodium (TBNa) and total
body chlorine (TBCl) in 81 normal adults. For the age span studied (30–90 years), the mean values of TBNa and TBCl remained
relatively constant for males, but decreased slightly for females beyond sixty years of age. In order to reduce the variability
in this cross-sectional study, the TBNa and TBCl values were normalized for body dimensions (weight, height, body surface
area) as well as age and sex. In addition, TBNa was related to skeletal mass (total body calcium) and lean body mass (total
body potassium). The quantity of body sodium in excess of the chlorine space was determined. This value, defined as sodium
excess, was significantly correlated with total body calcium. The values for total body sodium, total body chlorine, and sodium
excess obtained in the present study were compared with values previously reported in the literature. 相似文献
6.
J. J. Kehayias 《Journal of Radioanalytical and Nuclear Chemistry》2000,244(1):219-224
Nutritional status of patients can be evaluated by monitoring changes in body composition, including depletion of protein and muscle, adipose tissue distribution and changes in hydration status, bone or cell mass. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. The fast neutrons are produced with a sealed deuterium-tritium (D-T) neutron generator. This method provides the most direct assessment of body composition. Non-bone phosphorus for muscle is measured by the 31P(n,)28Al reaction, and nitrogen for protein via the (n,2n) fast neutron reaction. Inelastic neutron scattering is used for the measurement of total body carbon and oxygen. Carbon is used to derive body fat, after subtracting carbon contributions due to protein, bone and glycogen. Carbon-to-oxygen (C/O) ratio is used to measure distribution of fat and lean tissue in the body and to monitor small changes of lean mass and its quality. In addition to evaluating the efficacy of new treatments, the system is used to study the mechanisms of lean tissue depletion with aging and to investigate methods for preserving function and quality of life in the elderly. 相似文献
7.
T. Vasilopoulou F. Tzika M. J. J. Koster-Ammerlaan I. E. Stamatelatos 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(3):731-737
A benchmark experiment was performed for Neutron Activation Analysis (NAA) of a large inhomogeneous sample. The reference
sample was developed in-house and consisted of SiO2 matrix and an Al–Zn alloy “inhomogeneity” body. Monte Carlo simulations were employed to derive appropriate correction factors
for neutron self-shielding during irradiation as well as self-attenuation of gamma rays and sample geometry during counting.
The large sample neutron activation analysis (LSNAA) results were compared against reference values and the trueness of the
technique was evaluated. An agreement within ±10% was observed between LSNAA and reference elemental mass values, for all
matrix and inhomogeneity elements except Samarium, provided that the inhomogeneity body was fully simulated. However, in cases
that the inhomogeneity was treated as not known, the results showed a reasonable agreement for most matrix elements, while
large discrepancies were observed for the inhomogeneity elements. This study provided a quantification of the uncertainties
associated with inhomogeneity in large sample analysis and contributed to the identification of the needs for future development
of LSNAA facilities for analysis of inhomogeneous samples. 相似文献
8.
The basic principle of comparing the sample
mass with the mass of a reference body in equilibrium gives the equal-armed
beam balance a unique accuracy. Main parameters characterising the suitability
of the instrument are measuring range, resolution and relative sensitivity
(resolution/maximum load). The historical development of the values of these
parameters achieved depended strongly on the practical need in those times.
Technically unfavourable scales of the oldest Egyptian dynasties (~3000
BC) could resolve mass differences of 1 g and had a relative sensitivity of
at least 10–3. More sophisticated instruments
from the 18th Dynasty (~1567–1320 BC) achieved
a relative sensitivity of 10–4 independent
of the size of the instrument. In 350 BC Aristotle clarified the theory of
the lever and at about 250 BC Archimedes used the balance for density determinations
of solids. The masterpiece of a hydrological balance was Al Chazini’s
'Balance of Wisdom’ built about 1120. Its relative sensitivity
was 2⋅10–5.
Real progress took
place when scientists like Lavoisier (1743–1794) founded modern chemistry.
At the end of the 19th century metrological balances
reached a relative sensitivity of 10–9 with
a maximum load of several kilogrammes. That seems to be the high end of sensitivity
of the classical mechanical beam balance with knife edges. Improvements took
place by electrodynamic compensation (Emich, Gast).
In 1909 Ehrenhaft
and Millikan could weigh particles of 10–15
g by means of electrostatic suspension. In 1957 Sauerbrey invented the oscillating
quartz crystal balance. By observing the frequency shift of oscillating carbon
nanotubes or of silica nanorods, masses or mass changes in the attogram or
zeptogram have been observed recently. 相似文献
9.
J. H. Augustson J. W. Haynes T. W. Sanders 《Journal of Radioanalytical and Nuclear Chemistry》1980,60(2):373-383
A method for the determination of uranium based on235U thermal neutron fission, has been developed and employed on samples of ashed fish tissue and seaweed. The method involves
a post-irradiation ion exchange separation of iodine isotopes. The 884 keV photopeak of134I is used for measurement. Uranium detection limits in the samples concerned have been estimated to be 1·10−8g in terms of natural uranium. The precision achieved in analysing several series of 3–5 samples was 4–10 per cent. The accuracy
of the method was tested by employing an independent neutron activation procedure based on239U measurement. The accuracy of both methods was checked by analysing NBS SRM 1571 ‘Orchard Leaves’. 相似文献
10.
Kehayias JJ 《Analytical and bioanalytical chemistry》2004,379(2):188-191
Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the 31P(n,)28Al reaction, and nitrogen for protein via the 14N(n,2n)13N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D–T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the quality of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment. 相似文献
11.
Moriarty M Lee A O'Connell B Kelleher A Keeley H Furey A 《Analytical and bioanalytical chemistry》2011,401(8):2481-2493
Serotonin is a major neurotransmitter and affects various functions both in the brain and in the rest of the body. It has
been demonstrated that altered serotinergic function is implicated in various psychiatric disorders including depression and
schizophrenia. Serotonin has also been implicated along with dopamine in attention deficit–hyperkinetic disorder (AD-HKD).
This study provides a versatile validated method for the analysis of serotonin, hydroxyindole acetic acid and dopamine in
urine using LC-MS/MS. This method was then used to quantify these analytes in a test group of 17 children diagnosed with severe
AD-HKD. This group was compared to a matched control group to investigate the possibility that one of these compounds may
be a potential biomarker for this condition. The developed method provided good linear calibration curves for the multiplex
assay of analytes in urine (0.05–3.27 nmol/L; R
2 ≥ 0.9977). Acceptable inter-day repeatability was achieved for all analytes with RSD values (n = 9) ranging from 1.1% to 9.3% over a concentration range of 0.11–3.27 μmol/L in urine. Excellent limits of detection (LOD)
and limits of quantitation (LOQ) were achieved with LODs of 8.8–18.2 nmol/L and the LOQs of 29.4–55.7 nmol/L for analytes
in urine. Recoveries were in the ranges of 98–104%, 100–106% and 91–107% for serotonin, 5-HIAA and dopamine, respectively.
An appropriate sample clean-up procedure for urine was developed to ensure efficient recovery and reproducibility on analysis.
Evaluation of matrix effects was also carried out and the influence of ion suppression on analytical results reported. Confirmatory
analysis was carried out on a linear trap quadrupole-Orbitrap mass spectrometer to obtain high mass accuracy data of the target
analytes in the clinical samples. 相似文献
12.
Glow discharge mass spectrometry (GD-MS) is an excellent technique for fast multi-element analysis of pure metals. In addition
to metallic impurities, non-metals also can be determined. However, the sensitivity for these elements can be limited due
to their high first ionization potentials. Elements with a first ionization potential close to or higher than that of argon,
which is commonly used as discharge gas in GD-MS analysis, are ionized with small efficiency only. To improve the sensitivity
of GD-MS for such elements, the influence of different glow-discharge parameters on the peak intensity of carbon, chlorine,
fluorine, nitrogen, phosphorus, oxygen, and sulfur in pure copper samples was investigated with an Element GD (Thermo Fisher
Scientific) GD-MS. Discharge current, discharge gas flow, and discharge gas composition, the last of which turned out to have
the greatest effect on the measured intensities, were varied. Argon–helium mixtures were used because of the very high potential
of He to ionize other elements, especially in terms of the high energy level of its metastable states. The effect of different
Ar–He compositions on the peak intensity of various impurities in pure copper was studied. With Ar–He mixtures, excellent
signal enhancements were achieved in comparison with use of pure Ar as discharge gas. In this way, traceable linear calibration
curves for phosphorus and sulfur down to the μg kg−1 range could be established with high sensitivity and very good linearity using pressed powder samples for calibration. This
was not possible when pure argon alone was used as discharge gas.
This contribution is based on a presentation given at the Colloquium for Analytical Atomic Spectroscopy (CANAS ’07) held March
18–21, 2007 in Constance, Germany. 相似文献
13.
C. Pickhardt I. B. Brenner J. S. Becker H.-J. Dietze 《Analytical and bioanalytical chemistry》2000,368(1):79-87
Laser ablation inductively coupled plasma mass spectrometry using a quadrupole-based mass spectrometer (LA-ICP-QMS) was applied
for the analysis of powdered zeolites (microporous aluminosilicates) used for clean-up procedures. For the quantitative determination
of trace element concentrations three geological reference materials, granite NIM-G, lujavrite NIM-L and syenite NIM-S, from
the National Institute for Metallurgy (South Africa) with a matrix composition corresponding to the zeolites were employed.
Both the zeolites and reference materials were fused with a lithium borate mixture to increase the homogeneity and to eliminate
mineralogical effects. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS
relative sensitivity coefficients (RSCs) of chemical elements and calibration curves were measured using the geostandards.
The experimentally obtained RSCs are in the range of 0.2-6 for all elements of interest. Calibration curves for trace elements
were measured without and with Li or Ti as internal standard element. With a few exceptions the regression coefficients of
the calibration curves are better than 0.993 with internal standardization. NIM-G granite reference material was employed
to evaluate the accuracy of the technique. Therefore, the measured concentrations were corrected with RSCs which were determined
using lujavrite reference material NIM-L. This quantification method provided analytical results with deviations of 1–11%
from the recommended and proposed values in granite reference material NIM-G, except for Co, Cs, La and Tb. The relative standard
deviation (RSD) of the determination of the trace element concentration (n = 5) is about 1% to 6% using Ti as internal standard
element. Detection limits of LA-ICP-QMS in the lower μg/g range (from 0.03 μg/g for Lu, Ta and Th to 7.3 μg/g for Cu, with
the exception of La) have been achieved for all elements of interest. Under the laser ablation conditions employed (λ: 266
nm, repetition frequency: 10 Hz, pulse energy: 10 mJ, laser power density: 6 × 109 W/cm2) fractionation effects of the determined elements relative to the internal standard element Ti were not observed.
Received: 7 April 2000 / Revised: 25 May 2000 / Accepted: 31 May 2000 相似文献
14.
Pitois A de las Heras LA Zampolli A Menichetti L Carlos R Lazzerini G Cionini L Salvatori PA Betti M 《Analytical and bioanalytical chemistry》2006,384(3):751-760
Boron neutron capture therapy (BNCT) is a bimodal radiotherapeutic treatment based on the irradiation of neoplastic tissues
with neutrons after the tissues have selectively accumulated molecules loaded with nuclides with large neutron capture cross-sections
(such boron-10). Boron-10 carriers have been tested to a limited extent, and clinical trials have been conducted on sulfhydryl
borane (10B-BSH) and boronophenylalanine (10B-BPA). However, precise and accurate measurements of boron-10 concentrations (0.1–100 μg/g) in specimens and samples of limited
size (μg scale) are needed in order to be able to biologically characterise new compounds in predictive tissue dosimetry,
toxicology and pharmacology studies as well as in clinical investigations. A new approach based on fast separation and detection
of 10B-BPA performed by coupling capillary electrophoresis to electrospray mass spectrometry is reported. This method allows the
quantitative analysis and characterisation of 10B-BPA in a short time with a high separation efficiency. Detection limits of 3 μM for 10B-BPA and 30 ng/mL for 10B were obtained with CE–ESI–MS. A quantification limit of 10 μM for 10B-BPA (100 ng/mL for 10B) was attained. The total boron-10 concentration was determined by high-resolution inductively coupled mass spectrometry
in order to validate the method. Boron-10 isotope measurements were carried out by HR–ICP–MS at medium resolution (R=4000)
due to the presence of an isobaric interference at mass 10. Good agreement was obtained between the values from CE–ESI–MS
and those from HR–ICP–MS. The method has been successfully used to determine the 10B-BPA in two lines of cultured cells. 相似文献
15.
As a new approach to rapid small-molecule analysis, surfactant-mediated matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry (MALDI–TOF-MS) was successfully used in the analysis of caffeine and the vitamins riboflavin, nicotinamide,
and pyridoxine in various energy drinks. Of five common MALDI matrices tested (α-cyano-4-hydroxycinnamic acid, sinapinic acid,
2,5-dihydroxybenzoic acid, dithranol, and 2′,4′,6′-trihydroxyacetophenone), α-cyano-4-hydroxycinnamic acid was found to be
most suitable for analysis of high-sugar-containing energy drinks. Cetyltrimethylammonium bromide (CTAB) surfactant was used
as a matrix-ion suppressor, at a matrix:surfactant mole ratio of approximately 500:1. The resulting mass spectra show very
few matrix-related ions, while analyte signals were clearly observed. For comparative purposes the same analytes were identified
and quantified in energy drinks by LC–ESI–MS with UV detection. Quantitatively the calibration curves of all four analytes
showed a marked improvement when the surfactant-mediated method was used compared with traditional MALDI–TOF-MS; correlation
coefficients of 0.989 (nicotinamide), 0.991 (pyridoxine), 0.983(caffeine) and 0.987 (riboflavin) were obtained. It was found
that in quantitation of the energy drink analytes the surfactant-mediated MALDI–TOF-MS results were comparable with those
from LC analysis. In reproducibility experiments RSD values ranged from 9.7 to 18.1%. The work has demonstrated that this
mass spectrometric approach can be used as a rapid screening technique for fortified drinks. 相似文献
16.
Use of some organic dyes in gamma irradiation dose determination 总被引:1,自引:0,他引:1
In the present work, the radiation-induced color bleaching of Remazol brilliant blue (RBB), Wegocet orange (WO), Methyl green
(Me G) and Thioflavine S (Th S) dyes solutions was studied. Solutions of these dyes in different solvents were found to obey
Beer’s law within certain concentration levels. The % color bleaching occurring in different dye solutions on using different
gamma irradiation doses was determined and the data obtained showed the existence of good linear relationships among them
in the four dye systems used. The linear sections lines were used as calibration curves for evaluating unknown gamma irradiation
doses. From the obtained results, it was concluded that RBB in water, WO in ethanol, Me G in butanol and Th S in 60% ethanol–water
mixture could be used for dose evaluation within the dose ranges 5–25 kGy for RBB, 20–90 kGy for WO, 10–70 kGy for Me G and
5–160 kGy for Th S. The sensitivity of the systems towards gamma radiations has been also reported. 相似文献
17.
During the past decade, inductively coupled plasma mass spectrometry (ICPMS) has evolved from a delicate research tool, intended
for the well-trained scientist only, into a more robust and well-established analytical technique for trace and ultra-trace
element determination, with a few thousand of instruments used worldwide. Despite this immense success, it should be realized
that in its ’standard configuration’– i.e. equipped with a pneumatic nebulizer for sample introduction and with a quadrupole
filter – ICPMS also shows a number of important limitations and disadvantages: (i) the occurrence of spectral interferences
may hamper accurate trace element determination, (ii) solid samples have to be taken into solution prior to analysis and (iii)
no information on the ‘chemical form’ in which an element appears can be obtained. Self-evidently, efforts have been and still
are made to overcome the aforementioned limitations to the largest possible extent. The application of a double focusing sector
field mass spectrometer in ICPMS instrumentation offers a higher mass resolution, such that spectral overlap can be avoided
to an important extent. Additionally, in a sector field instrument, photons are efficiently eliminated from the ion beam,
resulting in very low background intensities, making it also very well-suited for extreme trace analysis. Also the combination
of the ICP as an ion source and a quadrupole filter operated in a so-called ‘alternate’ stability region, an ion trap or a
Fourier transform ion cyclotron resonance mass spectrometer allows high(er) mass resolution to be obtained. With modern quadrupole-based
instruments, important types of spectral interferences can be avoided by working under ‘cool plasma’ conditions or by applying
a collision cell. The use of electrothermal vaporization (ETV) or especially laser ablation (LA) for sample introduction permits
direct analysis of solid samples with sufficient accuracy for many purposes. The application range of LA-ICPMS has become
very wide and the introduction of UV lasers has led to an improved spatial resolution. Solid sampling ETV-ICPMS on the other
hand can be used for some specific applications only, but accurate calibration is more straightforward than with LA-ICPMS.
Limited multi-element capabilities, resulting from the transient signals observed with ETV or single shot LA, can be avoided
by the use of a time-of-flight (TOF) ICPMS instrument. Finally, when combined with a powerful chromatographic separation technique,
an ICP-mass spectrometer can be used as a highly sensitive, element-specific multi-element detector in elemental speciation
studies. Especially liquid (HPLC-ICPMS) and – to a lesser extent – gas (GC-ICPMS) chromatography have already been widely
used in combination with ICPMS. In speciation work, sample preparation is often observed to be troublesome and this aspect
is presently receiving considerable attention. For GC-ICPMS, new sample pretreatment approaches, such as headspace solid phase
microextraction (headspace SPME) and the purge-and-trap technique have been introduced. Also supercritical fluid chromatography
(SFC) and capillary electrophoresis (CE) show potential to be of use in combination with ICPMS, but so far the application
ranges of SFC-ICPMS and CE-ICPMS are rather limited. It is the aim of the present paper to concisely discuss the aforementioned
recent ’trends’ in ICPMS, using selected real-life applications reported in the literature.
Received: 30 November 1998 / Revised: 22 March 1999 / Accepted: 24 March 1999 相似文献
18.
Sergei F. Boulyga J. Sabine Becker Alexander F. Malenchenko Hans-Joachim Dietze 《Mikrochimica acta》2000,134(3-4):215-222
As a result of the Chernobyl nuclear power plant accident in 1986, thyroid pathologies occurred among children in some regions
of Belarus. Besides the irradiation of children’s thyroids by radioactive iodine and caesium nuclides, toxic elements from
fallout are a direct risk to health. Inductively coupled plasma quadrupole-based mass spectrometry was used for multielement
determination in small amounts (1–10 mg) of thyroid tissue samples obtained during thyroid operations in Minsk hospitals.
The accuracy of the applied analytical technique for small biological sample amounts was checked using NIST Standard Reference
Material oyster tissue (SRM 1566b) and by comparison with independent analytical methods, such as neutron activation analysis.
Almost all essential elements as well as a number of toxic elements such as Cd, Pb, Hg, U etc. were determined in a multitude
of human and animal thyroid tissues (up to 1 mg sample material) by quadrupole-based ICP-MS using micronebulization. In general,
the thyroid tissue affected by pathology is characterized by higher calcium content. Some other elements, among them Fe, Mn,
V, As, Cr, Ni, Pb, U, Ba, Sb, were also accumulated in such tissue. The results obtained will be used as initial material
for further specific studies of the role of particular elements in thyroid pathology development.
Received November 15, 1999. Revision March 15, 2000. 相似文献
19.
N. A. Maiorova E. K. Tuseeva V. E. Sosenkin A. Yu. Rychagov Yu. M. Vol’fkovich A. V. Krestinin G. I. Zvereva O. M. Zhigalina O. A. Khazova 《Russian Journal of Electrochemistry》2009,45(9):1089-1097
The structure and hydrophilic-hydrophobic properties of functionalized single-wall carbon nanotubes are studied by the standard
porosimetry method. It is shown that the functionalized nanotubes have highly hydrophilic surface; at that the summary surface
area measured “by octane” decreased, as a result of the functionalizing, due to the blocking of the nanotubes’ inner channels
by the functional groups located at the nanotubes’ ends. The nanotubes’ capacitive properties are studied; their charging-discharging
curves appeared being highly reversible, unlike those of other carbonaceous materials. Catalytic properties of the functionalized
nanotubes are studied, with particular tendency toward their using as a carrier of platinum catalysts for the methanol oxidation
and oxygen electroreduction reactions. When minor amounts (5–10 μg cm−2) of platinum or platinum-ruthenium alloy are deposited onto the nanotubes’ hydrophilic surface, uniform layer of the catalyst
is formed, with specific surface area up to 150–300 m2 g−1; high current of the methanol oxidation or oxygen electroreduction is observed at these catalysts. When the catalyst deposit
mass increased, its specific surface area decreased, as well as the specific current of the reactions occurring thereon. When
the current is related to the electrochemically active unit surface, the catalytic activity is nearly the same both for different
catalyst mass deposited onto the nanotubes and the same catalyst mass at different carbonaceous carriers. 相似文献
20.
Vyacheslav N. Fishman Bruno Linclau Dennis P. Curran Kasi V. Somayajula 《Journal of the American Society for Mass Spectrometry》2001,12(9):1050-1054
A new fluorinated compound mixture has been developed for the calibration of the double focusing mass spectrometer in the mass range of 100–3000 Da in the positive electron ionization (EI) mode. Current calibration standards for EI have either limited mass range [perfluorotributylamine (PFTBA), perfluorokerosene (PFK), s-triazines (TRIS)] or poor peak intensities with significant chemical background in the instrument for several days (perfluoroalkyl phosphazine). The newly synthesized fluorinated silyl alkyl amines mixture is proposed as a reference/calibration standard for EI-MS. This standard produced abundant parent and fragment ions across the entire mass range without any memory effect. 相似文献