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USGS2016

Updated atomic weights: Time to review our table

Despite common belief, atomic weights are not necessarily constants of nature. Scientists’ ability to measure these values is regularly improving, so one would expect that the accuracy of these values should be improving with time. It is the task of the IUPAC (International Union of Pure and Applied Chemistry) Commission on Isotopic Abundances and Atomic Weights (CIAAW) to regularly review atomic-weight determinations and release updated values. According to an evaluation published in Pure and Applied Chemistry [1], even the most simplified table abridged to four significant digits needs to be updated for the elements selenium and molybdenum. According to the most recent 2015 release of "Atomic Weights of the Elements" [2], another update is needed for ytterbium.

ChemistryViews Magazine↗

USGS2016

Isotopic compositions of the elements 2013 (IUPAC Technical Report)

The Commission on Isotopic Abundances and Atomic Weights (ciaaw.org) of the International Union of Pure and Applied Chemistry (iupac.org) has revised the Table of Isotopic Compositions of the Elements (TICE). The update involved a critical evaluation of the recent published literature. The new TICE 2013 includes evaluated data from the “best measurement” of the isotopic abundances in a single sample, along with a set of representative isotopic abundances and uncertainties that accommodate known variations in normal terrestrial materials.

Pure and Applied Chemistry↗

USGS2022

Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)

Stable hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS) isotope compositions expressed as isotope-delta values are typically reported relative to international standards such as Vienna Standard Mean Ocean Water (VSMOW), Vienna Peedee belemnite (VPDB) or Vienna Cañon Diablo Troilite (VCDT). These international standards are chosen by convention and the calibration methods used to realise them in practice undergo occasional changes. To ensure longevity and reusability of published data, a comprehensive description of (1) analytical procedure, (2) traceability, (3) data processing, and (4) uncertainty evaluation is required. Following earlier International Union of Pure and Applied Chemistry documents on terminology and notations, this paper proposes minimum requirements for publishing HCNOS stable-isotope delta results. Each of the requirements are presented with illustrative examples.

Pure and Applied Chemistry↗

USGS2022

Standard atomic weights of the elements 2021 (IUPAC Technical Report)

Following the reviews of atomic-weight determinations and other cognate data in 2015, 2017, 2019 and 2021, the IUPAC (International Union of Pure and Applied Chemistry) Commission on Isotopic Abundances and Atomic Weights (CIAAW) reports changes of standard atomic weights. The symbol A r °(E) was selected for standard atomic weight of an element to distinguish it from the atomic weight of an element E in a specific substance P, designated A r (E, P). The CIAAW has changed the values of the standard atomic weights of five elements based on recent determinations of terrestrial isotopic abundances: Ar (argon): from 39.948 ± 0.001 to [39.792, 39.963] Hf (hafnium): from 178.49 ± 0.02 to 178.486 ± 0.006 Ir (iridium): from 192.217 ± 0.003 to 192.217 ± 0.002 Pb (lead): from 207.2 ± 0.1 to [206.14, 207.94] Yb (ytterbium): from 173.054 ± 0.005 to 173.045 ± 0.010 The standard atomic weight of argon and lead have changed to an interval to reflect that the natural variation in isotopic composition exceeds the measurement uncertainty of A r (Ar) and A r (Pb) in a specific substance. The standard atomic weights and/or the uncertainties of fourteen elements have been changed based on the Atomic Mass Evaluations 2016 and 2020 accomplished under the auspices of the International Union of Pure and Applied Physics (IUPAP). A r ° of Ho, Tb, Tm and Y were changed in 2017 and again updated in 2021: Al (aluminium), 2017: from 26.981 5385 ± 0.000 0007 to 26.981 5384 ± 0.000 0003 Au (gold), 2017: from 196.966 569 ± 0.000 005 to 196.966 570 ± 0.000 004 Co (cobalt), 2017: from 58.933 194 ± 0.000 004 to 58.933 194 ± 0.000 003 F (fluorine), 2021: from 18.998 403 163 ± 0.000 000 006 to 18.998 403 162 ± 0.000 000 005 (Ho (holmium), 2017: from 164.930 33 ± 0.000 02 to 164.930 328 ± 0.000 007) Ho (holmium), 2021: from 164.930 328 ± 0.000 007 to 164.930 329 ± 0.000 005 Mn (manganese), 2017: from 54.938 044 ± 0.000 003 to 54.938 043 ± 0.000 002 Nb (niobium), 2017: from 92.906 37 ± 0.000 02 to 92.906 37 ± 0.000 01 Pa (protactinium), 2017: from 231.035 88 ± 0.000 02 to 231.035 88 ± 0.000 01 Pr (praseodymium), 2017: from 140.907 66 ± 0.000 02 to 140.907 66 ± 0.000 01 Rh (rhodium), 2017: from 102.905 50 ± 0.000 02 to 102.905 49 ± 0.000 02 Sc (scandium), 2021: from 44.955 908 ± 0.000 005 to 44.955 907 ± 0.000 004 (Tb (terbium), 2017: from 158.925 35 ± 0.000 02 to 158.925 354 ± 0.000 008) Tb (terbium), 2021: from 158.925 354 ± 0.000 008 to 158.925 354 ± 0.000 007 (Tm (thulium), 2017: from 168.934 22 ± 0.000 02 to 168.934 218 ± 0.000 006) Tm (thulium), 2021: from 168.934 218 ± 0.000 006 to 168.934 219 ± 0.000 005 (Y (yttrium), 2017: from 88.905 84 ± 0.000 02 to 88.905 84 ± 0.000 01) Y (yttrium), 2021: from 88.905 84 ± 0.000 01 to 88.905 838 ± 0.000 002

Pure and Applied Chemistry↗

USGS2009

History of the recommended atomic-weight values from 1882 to 1997: A comparision of differences from current values to the estimated uncertainties of earlier values

International commissions and national committees for atomic weights (mean relative atomic masses) have recommended regularly updated, best values for these atomic weights as applicable to terrestrial sources of the chemical elements. Presented here is a historically complete listing starting with the values in F. W. Clarke's 1882 recalculation, followed by the recommended values in the annual reports of the American Chemical Society's Atomic Weights Commission. From 1903, an International Commission published such reports and its values (scaled to an atomic weight of 16 for oxygen) are here used in preference to those of national committees of Britain, Germany, Spain, Switzerland, and the U.S.A. We have, however, made scaling adjustments from Ar(16O) to Ar(12C) where not negligible. From 1920, this International Commission constituted itself under the International Union of Pure and Applied Chemistry (IUPAC). Since then, IUPAC has published reports (mostly biennially) listing the recommended atomic weights, which are reproduced here. Since 1979, these values have been called the "standard atomic weights" and, since 1969, all values have been published, with their estimated uncertainties. Few of the earlier values were published with uncertainties. Nevertheless, we assessed such uncertainties on the basis of our understanding of the likely contemporary judgement of the values' reliability. While neglecting remaining uncertainties of 1997 values, we derive "differences" and a retrospective index of reliability of atomic-weight values in relation to assessments of uncertainties at the time of their publication. A striking improvement in reliability appears to have been achieved since the commissions have imposed upon themselves the rule of recording estimated uncertainties from all recognized sources of error.

Pure and Applied Chemistry↗

USGS2009

Isotope-abundance variations of selected elements (IUPAC technical report)

Pure and Applied Chemistry↗

USGS2018

IUPAC Periodic Table of the Elements and Isotopes (IPTEI) for the education community (IUPAC Technical Report)

The IUPAC (International Union of Pure and Applied Chemistry) Periodic Table of the Elements and Isotopes (IPTEI) was created to familiarize students, teachers, and non-professionals with the existence and importance of isotopes of the chemical elements. The IPTEI is modeled on the familiar Periodic Table of the Chemical Elements. The IPTEI is intended to hang on the walls of chemistry laboratories and classrooms. Each cell of the IPTEI provides the chemical name, symbol, atomic number, and standard atomic weight of an element. Color-coded pie charts in each element cell display the stable isotopes and the relatively long lived radioactive isotopes having characteristic terrestrial isotopic compositions that determine the standard atomic weight of each element. The background color scheme of cells categorizes the 118 elements into four groups: (1) white indicates the element has no standard atomic weight, (2) blue indicates the element has only one isotope that is used to determine its standard atomic weight, which is given as a single value with an uncertainty, (3) yellow indicates the element has two or more isotopes that are used to determine its standard atomic weight, which is given as a single value with an uncertainty, and (4) pink indicates the element has a well-documented variation in its atomic weight, and the standard atomic weight is expressed as an interval. An element-by-element review accompanies the IPTEI and includes a chart of all known stable and radioactive isotopes for each element. Practical applications of isotopic measurements and technologies are included for the following fields: forensic science, geochronology, Earth-system sciences, environmental science, and human health sciences, including medical diagnosis and treatment.

Pure and Applied Chemistry↗

USGS2003

Atomic weights of the elements. Review 2000 (IUPAC Technical Report)

A consistent set of internationally accepted atomic weights has long been an essential aim of the scientific community because of the relevance of these values to science and technology, as well as to trade and commerce subject to ethical, legal, and international standards. The standard atomic weights of the elements are regularly evaluated, recommended, and published in updated tables by the Commission on Atomic Weights and Isotopic Abundances (CAWIA) of the International Union of Pure and Applied Chemistry (IUPAC). These values are invariably associated with carefully evaluated uncertainties. Atomic weights were originally determined by mass ratio measurements coupled with an understanding of chemical stoichiometry, but are now based almost exclusively on knowledge of the isotopic composition (derived from isotope-abundance ratio measurements) and the atomic masses of the isotopes of the elements. Atomic weights and atomic masses are now scaled to a numerical value of exactly 12 for the mass of the carbon isotope of mass number 12. Technological advances in mass spectrometry and nuclear-reaction energies have enabled atomic masses to be determined with a relative uncertainty of better than 1 ×10−7 . Isotope abundances for an increasing number of elements can be measured to better than 1 ×10−3 . The excellent precision of such measurements led to the discovery that many elements, in different specimens, display significant variations in their isotope-abundance ratios, caused by a variety of natural and industrial physicochemical processes. While such variations increasingly place a constraint on the uncertainties with which some standard atomic weights can be stated, they provide numerous opportunities for investigating a range of important phenomena in physical, chemical, cosmological, biological, and industrial processes. This review reflects the current and increasing interest of science in the measured differences between source-specific and even sample-specific atomic weights. These relative comparisons can often be made with a smaller uncertainty than is achieved in the best calibrated “absolute ” (=SI-traceable) atomic-weight determinations. Accurate determinations of the atomic weights of certain elements also influence the values of fundamental constants such as the Avogadro, Faraday, and universal gas constants. This review is in two parts: the first summarizes the development of the science of atomic-weight determinations during the 20th century; the second summarizes the changes and variations that have been recognized in the values and uncertainties of atomic weights, on an element-by-element basis, in the latter part of the 20th century.

Pure and Applied Chemistry↗

USGS2009

Comprehensive inter-laboratory calibration of reference materials for δ18O versus VSMOW using various on-line high-temperature conversion techniques

Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high-temperature conversion techniques (HTC) in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125‰, an artificially enriched reference water ( δ 18 O of +78.91‰) and two barium sulfates (one depleted and one enriched in 18 O) were prepared and calibrated relative to VSMOW2 and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded: Reference material δ 18 O and estimated combined uncertainty IAEA-602 benzoic acid +71.28 ± 0.36‰ USGS35 sodium nitrate +56.81 ± 0.31‰ IAEA-NO-3 potassium nitrate +25.32 ± 0.29‰ IAEA-601 benzoic acid +23.14 ± 0.19‰ IAEA-SO-5 barium sulfate +12.13 ± 0.33‰ NBS 127 barium sulfate +8.59 ± 0.26‰ VSMOW2 water 0‰ IAEA-600 caffeine −3.48 ± 0.53‰ IAEA-SO-6 barium sulfate −11.35 ± 0.31‰ USGS34 potassium nitrate −27.78 ± 0.37‰ SLAP water −55.5‰ The seemingly large estimated combined uncertainties arise from differences in instrumentation and methodology and difficulty in accounting for all measurement bias. They are composed of the 3-fold standard errors directly calculated from the measurements and provision for systematic errors discussed in this paper. A primary conclusion of this study is that nitrate samples analyzed for δ 18 O should be analyzed with internationally distributed isotopic nitrates, and likewise for sulfates and organics. Authors reporting relative differences of oxygen-isotope ratios ( δ 18 O) of nitrates, sulfates, or organic material should explicitly state in their reports the δ 18 O values of two or more internationally distributed nitrates (USGS34, IAEA-NO-3, and USGS35), sulfates (IAEA-SO-5, IAEA-SO-6, and NBS 127), or organic material (IAEA-601 benzoic acid, IAEA-602 benzoic acid, and IAEA-600 caffeine), as appropriate to the material being analyzed, had these reference materials been analyzed with unknowns. This procedure ensures that readers will be able to normalize the δ 18 O values at a later time should it become necessary. The high-temperature reduction technique for analyzing δ 18 O and δ 2 H is not as widely applicable as the well-established combustion technique for carbon and nitrogen stable isotope determination. To obtain the most reliable stable isotope data, materials should be treated in an identical fashion; within the same sequence of analyses, samples should be compared with working reference materials that are as similar in nature and in isotopic composition as feasible.

Rapid Communications in Mass Spectrometry↗

USGS2011

Guidelines and recommended terms for expression of stable-isotope-ratio and gas-ratio measurement results

To minimize confusion in the expression of measurement results of stable isotope and gas-ratio measurements, recommendations based on publications of the Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) are presented. Whenever feasible, entries are consistent with the Système International d'Unités, the SI (known in English as the International System of Units), and the third edition of the International Vocabulary of Basic and General Terms in Metrology (VIM, 3rd edition). The recommendations presented herein are approved by the Commission on Isotopic Abundances and Atomic Weights and are designed to clarify expression of quantities related to measurement of isotope and gas ratios to ensure that quantity equations instead of numerical value equations are used for quantity definitions. Examples of column headings consistent with quantity calculus (also called the algebra of quantities) and examples of various deprecated usages connected with the terms recommended are presented.

Rapid Communications in Mass Spectrometry↗

USGS2015

Normalization of stable isotope data for carbonate minerals: implementation of IUPAC guideline

Carbonate minerals provide a rich source of geochemical information because their δ 13 C and δ 18 O values provide information about surface and subsurface Earth processes. However, a significant problem is that the same δ 18 O value is not reported for the identical carbonate sample when analyzed in different isotope laboratories in spite of the fact that the International Union of Pure and Applied Chemistry (IUPAC) has provided reporting guidelines for two decades. This issue arises because (1) the δ 18 O measurements are performed on CO 2 evolved by reaction of carbonates with phosphoric acid, (2) the acid-liberated CO 2 is isotopically fractionated (enriched in 18 O) because it contains only two-thirds of the oxygen from the solid carbonate, (3) this oxygen isotopic fractionation factor is a function of mineralogy, temperature, concentration of the phosphoric acid, and δ 18 O value of water in the phosphoric acid, (4) researchers may use any one of an assortment of oxygen isotopic fractionation factors that have been published for various minerals at various reaction temperatures, and (5) it sometimes is not clear how one should calculate δ 18 O VPDB values on a scale normalized such that the δ 18 O value of SLAP reference water is −55.5 &permil; relative to VSMOW reference water. To enable researchers worldwide to publish the same δ 18 O value (within experimental uncertainty) for the same carbonate sample, we have re-evaluated reported acid fractionation factors for calcite at 25, 50, and 75 °C and propose a revised relation for the temperature dependence of oxygen isotopic acid fractionation factor, α CO 2 ( ACID ) -calcite αCO2(ACID)-calcite , of 1000ln α CO 2 ( ACID ) -calcite=3.48(10 3 /T)-1.47 1000lnαCO2(ACID)-calcite=3.48(103/T)-1.47 Turn MathJax on where T is temperature in kelvin. At 25 °C, α CO 2 ( ACID ) -calcite=1.01025 αCO2(ACID)-calcite=1.01025 , the most commonly accepted value for this quantity. We propose a normalization protocol in which (1) the internationally distributed carbonate isotopic reference materials NBS 18 and NBS 19 are interspersed among carbonate samples analyzed by treatment with phosphoric acid, (2) the δ 18 O values of the calcite reference materials and the carbonate samples are calculated, respectively, by using the α CO 2 ( ACID ) -calcite αCO2(ACID)-calcite relation above and oxygen-isotope acid fractionation factors appropriate for the sample mineralogy and reaction temperature, (3) the δ 18 O values of solid carbonate samples are determined on the VPDB scale ( δ 18 O VPDB ) with IUPAC-recommended scale expansion such that the δ 18 O of SLAP reference water is −55.5 &permil; relative to VSMOW reference water by normalizing δ 18 O values of carbonate samples with 2014-IUPAC-recommended δ 18 O values of NBS 18 and NBS 19, and (4) δ 18 O values on the VPDB scale are converted to δ 18 O values on the VSMOW-SLAP scale by using IUPAC recommendations. To ease calculations in the protocol, a software application titled “Carbon and Oxygen Isotopic Normalization Tool for Carbonates” is available that relies upon IUPAC-recommended δ 13 C and δ 18 O values of carbonate isotopic reference materials ( http://isotopes.usgs.gov/research/topics/carbonatesnormalizationtool.html ).

Geochimica et Cosmochimica Acta↗

USGS2017

Clarifying atomic weights: A 2016 four-figure table of standard and conventional atomic weights

To indicate that atomic weights of many elements are not constants of nature, in 2009 and 2011 the Commission on Isotopic Abundances and Atomic Weights (CIAAW) of the International Union of Pure and Applied Chemistry (IUPAC) replaced single-value standard atomic weight values with atomic weight intervals for 12 elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine, and thallium); for example, the standard atomic weight of nitrogen became the interval [14.00643, 14.00728]. CIAAW recognized that some users of atomic weight data only need representative values for these 12 elements, such as for trade and commerce. For this purpose, CIAAW provided conventional atomic weight values, such as 14.007 for nitrogen, and these values can serve in education when a single representative value is needed, such as for molecular weight calculations. Because atomic weight values abridged to four figures are preferred by many educational users and are no longer provided by CIAAW as of 2015, we provide a table containing both standard atomic weight values and conventional atomic weight values abridged to four figures for the chemical elements. A retrospective review of changes in four-digit atomic weights since 1961 indicates that changes in these values are due to more accurate measurements over time or to the recognition of the impact of natural isotopic fractionation in normal terrestrial materials upon atomic weight values of many elements. Use of the unit “u” (unified atomic mass unit on the carbon mass scale) with atomic weight is incorrect because the quantity atomic weight is dimensionless, and the unit “amu” (atomic mass unit on the oxygen scale) is an obsolete term: Both should be avoided.

Journal of Chemical Education↗

USGS2005

Isotopic compositions of the elements, 2001

The Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry completed its last review of the isotopic compositions of the elements as determined by isotope-ratio mass spectrometry in 2001. That review involved a critical evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compositions of the elements (TICE) presented here. For each element, TICE includes evaluated data from the “best measurement” of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the standard atomic weight of the element A r ( E ) "> A r ( E ) Ar(E) and its uncertainty U[A r ( E )] "> U[A r ( E )] U[Ar(E)] recommended by CAWIA in 2001.

Journal of Physical and Chemical Reference Data↗

USGS2006

Description, Properties, and Degradation of Selected Volatile Organic Compounds Detected in Ground Water--A Review of Selected Literature

This report provides abridged information describing the most salient properties and biodegradation of 27 chlorinated volatile organic compounds detected during ground-water studies in the United States. This information is condensed from an extensive list of reports, papers, and literature published by the U.S. Government, various State governments, and peer-reviewed journals. The list includes literature reviews, compilations, and summaries describing volatile organic compounds in ground water. This report cross-references common names and synonyms associated with volatile organic compounds with the naming conventions supported by the International Union of Pure and Applied Chemistry. In addition, the report describes basic physical characteristics of those compounds such as Henry's Law constant, water solubility, density, octanol-water partition (log Kow), and organic carbon partition (log Koc) coefficients. Descriptions and illustrations are provided for natural and laboratory biodegradation rates, chemical by-products, and degradation pathways.

Open-File Report↗

USGS2002

Compilation of minimum and maximum isotope ratios of selected elements in naturally occurring terrestrial materials and reagents

Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope abundance variations potentially are large enough to result in future expansion of their atomic weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope-abundance variations in materials of natural terrestrial origin are too small to have a significant effect on their standard atomic weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio. There are no internationally distributed isotopic reference materials for the elements zinc, selenium, molybdenum, palladium, and tellurium. Preparation of such materials will help to make isotope ratio measurements among laboratories comparable. The minimum and maximum concentrations of a selected isotope in naturally occurring terrestrial materials for selected chemical elements reviewed in this report are given below: Isotope Minimum mole fraction Maximum mole fraction -------------------------------------------------------------------------------- 2H 0 .000 0255 0 .000 1838 7Li 0 .9227 0 .9278 11B 0 .7961 0 .8107 13C 0 .009 629 0 .011 466 15N 0 .003 462 0 .004 210 18O 0 .001 875 0 .002 218 26Mg 0 .1099 0 .1103 30Si 0 .030 816 0 .031 023 34S 0 .0398 0 .0473 37Cl 0 .240 77 0 .243 56 44Ca 0 .020 82 0 .020 92 53Cr 0 .095 01 0 .095 53 56Fe 0 .917 42 0 .917 60 65Cu 0 .3066 0 .3102 205Tl 0 .704 72 0 .705 06 The numerical values above have uncertainties that depend upon the uncertainties of the determinations of the absolute isotope-abundance variations of reference materials of the elements. Because reference materials used for absolute isotope-abundance measurements have not been included in relative isotope abundance investigations of zinc, selenium, molybdenum, palladium, and tellurium, ranges in isotopic composition are not listed for these elements, although such ranges may be measurable with state-of-the-art mass spectrometry. This report is available at the url: http://pubs.water.usgs.gov/wri014222.

Water-Resources Investigations Report↗

USGS2010

Atomic weights of the elements 2009 (IUPAC technical report)

The biennial review of atomic-weight determinations and other cognate data has resulted in changes for the standard atomic weights of 11 elements. Many atomic weights are not constants of nature, but depend upon the physical, chemical, and nuclear history of the material. The standard atomic weights of 10 elements having two or more stable isotopes have been changed to reflect this variability of atomic-weight values in natural terrestrial materials. To emphasize the fact that these standard atomic weights are not constants of nature, each atomic-weight value is expressed as an interval. The interval is used together with the symbol [a; b] to denote the set of atomic-weight values, A r (E), of element E in normal materials for which a ≤ A r (E) ≤ b. The symbols a and b denote the bounds of the interval [a; b]. The revised atomic weight of hydrogen, A r (H), is [1.007 84; 1.008 11] from 1.007 94(7); lithium, A r (Li), is [6.938; 6.997] from 6.941(2); boron, A r (B), is [10.806; 10.821] from 10.811(7); carbon, A r (C), is [12.0096; 12.0116] from 12.0107(8); nitrogen, A r (N), is [14.006 43; 14.007 28] from 14.0067(2); oxygen, A r (O), is [15.999 03; 15.999 77] from 15.9994(3); silicon, A r (Si), is [28.084; 28.086] from 28.0855(3); sulfur, A r (S), is [32.059; 32.076] from 32.065(2); chlorine, A r (Cl), is [35.446; 35.457] from 35.453(2); and thallium, A r (Tl), is [204.382; 204.385] from 204.3833(2). This fundamental change in the presentation of the atomic weights represents an important advance in our knowledge of the natural world and underscores the significance and contributions of chemistry to the well-being of humankind in the International Year of Chemistry 2011. The standard atomic weight of germanium, A r (Ge), was also changed to 72.63(1) from 72.64(1).

Pure and Applied Chemistry↗

USGS2010

Correction for the 17O interference in δ(13C) measurements when analyzing CO2 with stable isotope mass spectrometry

Measurements of δ( 13 C) determined on CO 2 with an isotope-ratio mass spectrometer (IRMS) must be corrected for the amount of 17 O in the CO 2 . For data consistency, this must be done using identical methods by different laboratories. This report aims at unifying data treatment for CO 2 IRMS by proposing (i) a unified set of numerical values, and (ii) a unified correction algorithm, based on a simple, linear approximation formula. Because the oxygen of natural CO 2 is derived mostly from the global water pool, it is recommended that a value of 0.528 be employed for the factor λ, which relates differences in 17 O and 18 O abundances. With the currently accepted N( 13 C)/N( 12 C) of 0.011 180(28) in VPDB (Vienna Peedee belemnite) reevaluation of data yields a value of 0.000 393(1) for the oxygen isotope ratio N( 17 O)/N( 16 O) of the evolved CO 2 . The ratio of these quantities, a ratio of isotope ratios, is essential for the 17 O abundance correction: [N( 17 O)/N( 16 O)]/[N( 13 C)/N( 12 C)] = 0.035 16(8). The equation [δ( 13 C) ≈ 45 δ VPDB-CO2 + 2 17 R/ 13 R ( 45 δ VPDB-CO2 – λ 46 δ VPDB-CO2 )] closely approximates δ( 13 C) values with less than 0.010 ‰ deviation for normal oxygen-bearing materials and no more than 0.026 ‰ in extreme cases. Other materials containing oxygen of non-mass-dependent isotope composition require a more specific data treatment. A similar linear approximation is also suggested for δ( 18 O). The linear approximations are easy to implement in a data spreadsheet, and also help in generating a simplified uncertainty budget.

Pure and Applied Chemistry↗

USGS2013

Errata: Atomic weights of the elements: Review 2000

No abstract available.

Pure and Applied Chemistry↗