Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027819 (neuroblastoma)
 27,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The application of cavity-ionization chambers to the standadization of 60Co gamma-ray beams, in terms of exposure, requires that the specific ionization of air Jg, be corrected for the attenuation and scatter of the incident rays by the wall, central electrode, and supporting stem of the chamber. A Monte Carlo photon-electron transport code has been developed for the purpose of calculating this correction for spherical and cylindrical chambers. The code has been applied to a spherical graphite chamber having dimensions typical of the chambers used by the NBS, the calculated wall-correction factor is in close agreement with the average of the NBS factors which were determined experimentally. The code was also used to calculate Aeq, which is central to the determination of tissue-air ratios. The calculated value, 0.989 +/- 0.003, is very close to the generally accepted value, 0.985.
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PMID:Monte Carlo calculation of the wall correction factors for ionization chambers and Aeq for 60Co gamma rays. 71 76

A method for determining As and Se in beef offal and fish was developed. The sample was digested by heating with a mixture of nitric, perchloric, and sulfuric acids. No pre-reduction of As and Se was necessary. Using a simplified generator, the metal hydrides were evolved by reduction with sodium borohydride pellets from sulfuric and hydrochloric acid media. The hydrides were swept by a flow of nitrogen into a nitrogen-hydrogen-entrained air flame. Absolute detection limit of the method was about 6 ng for As and 4 ng for Se, and absolute sensitivity for both metals was estimated to be 5 ng. Effects of the presence of several cations and anions in the matrix were investigated and some were found to have a suppressive effect on the atomic absorption signal. The analytical results obtained for samples of NBS No. 1571 Orchard Leaves and NBS No. 1577 Bovine Liver agreed well with certified values.
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PMID:Atomic absorption spectrometric determination of arsenic and selenium in offal and fish by hydride generation. 72 42

Utilizing the recently described reference method for calcium (NBS-AACC) and the recently developed definitive (referee) NBS method for serum calcium measurement by isotopedilution mass spectrometry (IDMS), an evaluation of five recent-model atomic absorption spectrometers was carried out. Under optimal conditions of instrument operation using aqueous standards, significant differences were found during the comparative analyses of three lyophilized pool samples and one liquid serum pool sample. Use of the NBS-AACC serum calcium protocol did not guarantee analytic results within +/- 2% of the IDMS value. In four of eight comparisons, differences from IDMS greater than 2% were observed. Several variables were studied to account for these differences. It was shown that a serum matrix, when present in standards used to bracket the unknown sample, reduced differences between instruments in four of four instances and improved the accuracy of the results from a range of -1.1 to +3.5% to +0.1 to +1.0%. It is concluded that a serum sample with a verified IDMS calcium value is a valuable tool that establishes an accurate and stable reference point for serum calcium measurement. The use of transfer-of-NBS-technology multipliers is suggested. Regional quality control serum pools and clinical chemistry survey sample materials that have been analyzed for calcium concentration by the NBS-IDMS definitive method are examples of these multipliers.
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PMID:Comparison of serum calcium measurements with respect to five models of atomic absorption spectrometers using NBS-AACC calcium reference method and isotope-dilution mass spectrometry as the definitive method. 78 97

1,2-Diaminobenzene and its derivatives react with selenous acid in acidic solution to form the piazselenols, which can be extracted into toluene. Microgram amounts of selenium can be determined spectrophotometrically by measuring the absorbance of these piazselenols extracted into toluene. A more sensitive method, in which the piazselenols extracted into toluene are detected by electron-capture gas chromatography, has been developed. In order to find a more sensitive reagent, 13 piazselenols were synthesized. The retention behaviour and sensitivity in electron-capture detection gas chromatography and the distribution ratios between aqueous solution and toluene were studied for each piazselenol extracted into toluene. Of these piazselenols, 4,6-dibromopiazselenol, formed by the reaction of 1,2-diamino-3,5-dibromobenzene with selenous acid, was found to be best as regards sensitivity and distribution ratio. Under the optimal conditions for the formation and the extraction of the piazselenol, the practical detection limit was 1 ng. Selenium(VI) and total selenium in NBS Bovine Liver, SRM 1577, were determined successfully.
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PMID:Some 1,2-diaminobenzene derivatives as reagents for gas chromatographic determination of selenium with an electron-capture detector. 88 62

An analytical method is presented for determining cadmium, copper, and lead by differential pulse anodic stripping voltammetry and zinc by cathodic scan differential pulse voltammetry. Food samples are dry ashed using a sulfuric acid ashing aid, dissolved in dilute nitric acid, buffered at pH approximately 4.3 with an acetate buffer, and quantitatively analyzed using the technique of standard additions at a hanging mercury drop electrode. The quantitation limits (5 times the estimated detection limits) are approximately 5 ng/g for Cd, Cu, and Pb, and 50 ng/g for Zn. Accuracy of the method is established by (a) analysis of NBS Standard Reference Material No. 1577 Bovine Liver, (b) comparison of results obtained by the method described with those obtained by independent analytical methods, and (c) quantitative recovery of analyte metals from fortified, noncanned food samples. Results from an interlaboratory method trial indicate that the method is suitable for the analysis of a variety of food types.
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PMID:Dry ash-voltammetric determination of cadmium, cooper, lead, and zinc in foods. 89 6

A method is described for determining selenium in fish tissues, meat, cereals, milk powder, and other materials by flameless atomic absorption spectrophotometry. Samples are solubilized in HNO3 and atomized in a graphite furnace in the presence of nickel nitrate. Recoveries of 0.500 and 1.000 microgram selenium added to several fish samples averaged 99.0 and 98.3%, respectively, with standard deviations of 5.3 and 4.0. Results agreed with those obtained for samples previously analyzed by fluorometry, and with results for NBS Standard Reference Material. The detection limit was 3 ng/ml solution and 50 ng/g sample.
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PMID:Flameless atomic absorption spectrophotometry of selenium in fish and food products. 89 19

Biomethylation of metals, including arsenic, apparently occurs as a global process. Health control strategies therefore depend on accurate analysis of arsenic's environmental mobility. Determining to what extent biotransformations occur and how resultant organometal(loids) are sequestered in food chains requires sophistication beyond present-day total element determinations. Rather, active molecular forms of arsenic must be speciated for each environmental compartment, and it is necessary to quantify the dynamics of arsenic's mobility. Thus, new chemical facts are needed yielding rates of methylation or demethylation of arsenic; partition coefficients of organoarsenicals between air, water, and organic phases; and arsenic redox chemistry in polar media. NBS research in this context is reviewed with examples of recent results emphasizing speciation methodology. Topic areas discussed are: the nature of aquated methylarsenic species (NMR and laser-Raman spectroscopy); transport of methylarsenicals from aqueous media (gas chromatography-graphic furnace AA detection applied to metabolic Me3As formation); and speciation of involatile organoarsenicals in aqueous media (demonstration of HPLC utilizing element-specific AA detection and appraisal of electrochemical detectors).
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PMID:Questions concerning environmental mobility of arsenic: needs for a chemical data base and means for speciation of trace organoarsenicals. 90 86

A method is described to determine selenium in biological material, based on cathodic stripping voltammetry. Following wet ashing, the selenium was extracted into benzene as the 3',4'-diaminophenylpiazselenol. The selenium was subsequently back-extracted into dilute acid for analysis. Analyses of NBS Bovine Liver demonstrated that the method was capable of recovering 96+/-9% of the selenium present. The detection limit and working range were 3 ng/g and 0-10,000 ng/g, respectively. The method was also applied to the determination of selenium in rapeseed oils and seed.
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PMID:Cathodic stripping voltammetry of nanogram amounts of selenium in biological material. 99 75

Pollution from the Kjeldahl method for crude protein has been reduced by substituting a low level of copper (0.04 g CuSO4) for the mercury (0.7 g HgO) specified in the AOAC official method, 2.049. Adjustments were made in the salt-acid ratio so the new system could handle hard-to-digest samples in a reasonable time. The new method was rugged for lysine. HCl. It is designed to be used for crude protein in feeds or similar Kjeldahl work. Precision and accuracy were equal to or better than that for the official method in a study of 17 samples analyzed in duplicate on 3 different days. The following samples were used in the study: lysine. HCl, tryptophan, NBS standards, urea, meals, mixed feeds, grains, and forage. The average per cent nitrogen found was 9.52 by the official method and 9.53 by the copper method. The average standard deviation was 0.038 by the official method and 0.033 by the copper method, giving the corresponding relative standard deviations of 0.40 and 0.35%.
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PMID:Pollution-reduced Kjeldahl method for crude protein. 103 79

We previously proposed that the assembly reaction of TMV in vitro is initiated by 20S protein aggregate specifically interacting to the 5'-end of TMV-RNA, after which the helical rod grows by the addition of protein subunits. Other workers have reported that the source of protein for the growing helix is also the 20S protein aggregate, but not protein subunits. We now summarize the experimental results that confirm our previous hypothesis. 1) TMV-particle, as gauged by infectivity assay and sucrose gradient analysis, could be formed from PRR under conditions where the formation of 20S protein aggregate could not occur. 2) TMV-particle could be formed from PRR by stepwise addition of NBS-modified protein which is lacking the ability to form 20S protein aggregate. 3) The stable disk aggregate of CGMMV-protein are unable to grow the helical rod. 4) The process of rod elongation by protein subunits was observed directly in electron micrography.
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PMID:Mechanism of assembly of tobacco mosaic virus in vitro. 110 55


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