ABSTRACT
Absolute values have been obtained for the isotopic abundance ratios of a reference sample of nickel (Standard Reference Material 986), using thermal ionization mass spectrometry. Samples of known isotopic composition, prepared from nearly isotopically pure separated nickel isotopes, were used to calibrate the mass spectrometers. The resulting absolute isotopic ratios are: 58Ni/60Ni=2.596061±0.000728, 61Ni/60Ni=0.043469±0.000015,62Ni/60Ni=0.138600±0.000045, and 64Ni/60Ni=0.035295±0.000024, which yield atom percents of 58Ni=68.076886 ±0.005919, 60Ni = 26.223146±0.005144,61Ni=1.139894±0.000433, 62Ni =3.634528±0.001142, and 64Ni =0.925546±0.000599. The atomic weight calculated from this isotopic composition is 58.693353 ±0.000147. The indicated uncertainties are overall limits of error based on two standard deviations of the mean and allowances for the effects of known sources of possible systematic error.
ABSTRACT
Twenty-nine samples of high-purity nickel metals, reagent salts and minerals, collected from worldwide sources, have been examined by high-precision isotope ratio mass spectrometry for their nickel isotopic composition. These materials were compared directly with SRM 986, certified isotopie standard for nickel, using identical measurement techniques and the same instrumentation. This survey shows no statistically significant variations among the samples investigated, indicating that the certified atomic weight and associated uncertainty for SRM 986 is applicable to terrestrial nickel samples. The atomic weight calculated for SRM 986 is 58.69335±0.00015 [2]. The currently recommended IUPAC value for terrestrial nickel is 58.69±0.01.
ABSTRACT
An absolute value has been obtained for the isotopic abundance ratio of a reference sample of gallium (Standard Reference Material 994), using thermal ionization mass spectrometry. Samples of known isotopic composition, prepared from nearly isotopically pure separated gallium isotopes, were used to calibrate the mass spectrometers. The resulting absolute 69Ga/71Ga ratio is 1.50676±0.00039, which yields atom percents of 69Ga=60.1079±0.0062 and 71Ga=39.8921±0.0062. The atomic weight calculated from this isotopic composition is 69.72307±0.00013. The indicated uncertainties are overall limits of error based on two standard deviations of the mean and allowances for the effects of known sources of possible systematic error.
ABSTRACT
Two case studies are presented which apply the lead isotope ratio method to the identification of lead sources in 12 Oakland, California children. One study examined lead sources in 10 children, ages 3 to 15 yr, living together as an extended family in dilapidated housing close to a busy freeway. Eight children had elevated blood lead levels (greater than or equal to 30 micrograms/dl) and 6 children also had elevated erythrocyte protoporphyrin levels (greater than or equal to 50 micrograms/dl). A second case study examined 2-yr-old male twins, both with elevated blood lead and erythrocyte protoporphyrin levels, living in a modest, but well maintained inner city duplex apartment. Paint and surface soil samples collected in and around both households had high lead concentrations. Paint concentrations ranged from 2.9 to 273 mg/g and surface soil concentrations from 0.48 to 7.1 mg/g. The isotopic ratios of lead in the blood of these children were close to the average lead ratios of paints from exterior walls and to the lead ratios of surface soils in adjacent areas where the children played. In both case studies, the data suggest that the lead in the soil was derived mainly from weathering of lead-based exterior paints and that the lead-contaminated soil was a proximate source of lead in the blood of the children.
Subject(s)
Lead/blood , Adolescent , California , Child , Child, Preschool , Environmental Exposure , Female , Humans , Isotopes , Male , Protoporphyrins/blood , Soil Pollutants/analysisABSTRACT
Thermal-ionization isotope-dilution mass spectrometry is a highly precise and accurate method for the determination of potassium concentrations in serum. Although not suited for routine use because of the time and expense required, the technique provides an extremely valuable tool for the characterization of reference materials and for evaluating other analytical methods. The technique has recently been used to determine the concentration of potassium in a human serum standard, NBS Standard Reference Material 909. Seven vials of the serum were chemically processed and then analyzed by two spectroscopists independently, using different mass spectrometers. The results confirm previous work that indicates that a precision of 0.1% relative can be routinely achieved. The systematic errors in the method have been thoroughly evaluated. When the precise results are thus corrected, they are essentially bias free and hence definitive.
Subject(s)
Potassium/blood , Freeze Drying , Humans , Mass Spectrometry , Radioisotope Dilution Technique , Reference Values , SodiumABSTRACT
The atomic weight of a reference sample of silver has been determined by mass speetrometry, with an uncertainty of one part in 106, using a single filament silica gel procedure. Accurately known quantities of chemically pure 107Ag and l09Ag were mixed to produce standards of known isotopic composition for calibration of the mass spectrometer. The absolute isotopic ratio of the reference sample of silver is 107Ag/109Ag = 1.07638 ± 0.00022 yielding an atomic weight of 107.86815 ± 0.00011. The indicated uncertainties represent an overall limit of error at the 95 percent confidence level which is the sum of the uncertainty components for the ratio determined and the components covering effects of known sources of possible systematic error.
ABSTRACT
A report of the Faraday constant as determined at NBS via silver coulometry and atomic weight measurements is presented. The uncertainty of the reported result represents a five-fold improvement over measurements made at NBS 20 years ago. The result should contribute to an analysis of the self-consistency of several other fundamental constants measurements. Experimental details have been reported in other publications which are cited in the text.
ABSTRACT
Radiochemical neutron activation analysis (RNAA) is compared with isotope ratio mass spectrometry (IRMS) for the measurement of 70Zn isotopic enrichment in human plasma following oral administration of the isotope. It is shown that both techniques are suitable for this purpose, although IRMS yields more precise data. Each method, with its advantages and limitations, can be realistically employed to study kinetics of appearance of 70Zn in plasma obtained during human metabolic studies.
Subject(s)
Zinc/blood , Humans , Kinetics , Mass Spectrometry/methods , Neutron Activation Analysis/methods , Zinc IsotopesABSTRACT
The accepted atomic weight of thallium has remained at a value of 204.37 ± 0.03 since 1962. At this level of uncertainty, however, the atomic weight becomes a limiting factor to high accuracy analysis. The new mass spectrometric determination of the atomic weight of thallium has been completed. A high precision assay technique was developed so that accurately known quantities of the 203Tl and 205Tl separated isotopes could be mixed to produce standards for calibration of the mass spectrometer. This assay technique involved the gravimetric determination of 99.3 percent of the0020thallium as Tl2CrO4. The soluble thallium was then aliquoted and determined by isotope dilution mass spectrometry. Before making up the final solutions from which the assay and calibration samples would be withdrawn, the separated isotopes were purified by solvent extraction and electrodeposition. A tungsten filament surface ionization technique was developed for the determination of precise isotopic abundance measurements for thallium. This technique allowed isotopic analysis of the separated isotopes, calibration standards, and a natural thallium reference standard with precisions of better than 0.1 percent. The 205Tl/2Tl absolute isotopic abundance ratio of the reference sample was found to be 2.38714 ± 0.00101, yielding an atomic weight of 204.38333 + 0.00018.
ABSTRACT
Solid sample, thermal ionization, mass spectrometry has been used to obtain absolute values for the isotopic abundance ratios of a reference sample of potassium. Standards of known isotopic composition, prepared by gravimetrically mixing nearly isotopically and chemically pure separated isotopes of, 39K and 41K, were used for calibration. The absolute isotopic abundance ratios are : 39K/41K = 13.8566 ± 0.0063 and 40K/41K = 0.0017343 ± 0.0000061 which yield atom percent compositions of 39K=93.2581 ± 0.0029. 40K = 0.01167 ± 0.00004, and 41K = 6.7302 ± 0.0029. The calculated atomic weight for potassium is 39.098304 ± 0.000058. The indicated uncertainties are overall limits of error which are the sum of the uncertainty components for ratio determinations and the components covering the effects of known sources of possible systematic error.
