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ISOTOPIC COMPOSITIONS OF THE ELEMENTS 1997 Abstract- The Commission's Subcommittee for the Isotopic Composition of the Elements(SIAM) has carried out its biennial review of isotopic compositions, as determined by mass spectrometry and other relevant methods. This involves a critical evaluation of the published literature, element by element, and forms the basis of the Table of Isotopic Compositions of the Elements as Determined by Mass Spectrometry presented here. New guidelines have been used to arrive at the uncertainties on the isotopic abundances and there are numerous changes to the Table since it was last published in 1991. Atomic Weights calculated from this table are consistent with Ar(E) values listed in the Table of Standard Atomic Weights 1997 INTRODUCTIO Previous compilations of"The isotopic compositions of the elements"were published in 1983(ref. 1) 1984(ref. 2)and 1991(ref. 3) for the purpose of yielding atomic weights consistent with the Commissions " Table of Standard Atomic Weights"[4, 5, 6 During the past six years the Commission, through its Subcommittee for Isotopic Abundance Measurements(SIAM), has continued to assemble and evaluate new data which has led to improvements to the tabulated isotopic composition of a number of elements. In 1993, the statistical guidelines for assigning uncertainties to the representative abundances were revised and extended by the Commissions Working Party on Statistical Evaluation of Isotopic Abundances(members: K J. R Rosman( Chairman) P De Bievre and J. w. Gramlich). All the data presented in the Table were reassessed according to these guidelines The present table was assembled for publication following the meeting of SIAM held at Kloster Seeor Germany), just prior to the 39th IUPAC General Assembly held at Geneva(Switzerland )in 1997 and is presented here as a companion paper to the Atomic Weights of the Elements 1997 REFERENCES 1. N.E. Holden, R L. Martin and I L. Barnes, Pure Appl. Chem., 55, 1119-1136(1983) 2. N.E. Holden, R.L. Martin and l.L. Barnes, Pure Appl. Chem., 56, 675-694(1984) 3. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 63, 991-1002 (1991) 4. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 55, 1101-1118 (1983) 5. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 56, 653-674 (1984) 6. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 63, 975-990 (1991)

ISOTOPIC COMPOSITIONS OF THE ELEMENTS 1997 Abstract- The Commission’s Subcommittee for the Isotopic Composition of the Elements (SIAM) has carried out its biennial review of isotopic compositions, as determined by mass spectrometry and other relevant methods. This involves a critical evaluation of the published literature, element by element, and forms the basis of the Table of Isotopic Compositions of the Elements as Determined by Mass Spectrometry presented here. New guidelines have been used to arrive at the uncertainties on the isotopic abundances and there are numerous changes to the Table since it was last published in 1991. Atomic Weights calculated from this table are consistent with Ar(E) values listed in the Table of Standard Atomic Weights 1997. INTRODUCTION Previous compilations of “The isotopic compositions of the elements” were published in 1983 (ref. 1), 1984 (ref. 2) and 1991 (ref. 3) for the purpose of yielding atomic weights consistent with the Commission's “Table of Standard Atomic Weights ” [4, 5, 6]. During the past six years the Commission, through its Subcommittee for Isotopic Abundance Measurements (SIAM), has continued to assemble and evaluate new data which has led to improvements to the tabulated isotopic composition of a number of elements. In 1993, the statistical guidelines for assigning uncertainties to the representative abundances were revised and extended by the Commission's Working Party on Statistical Evaluation of Isotopic Abundances (members: K. J. R. Rosman (Chairman), P. De Bièvre and J. W. Gramlich). All the data presented in the Table were reassessed according to these guidelines. The present table was assembled for publication following the meeting of SIAM held at Kloster Seeon (Germany), just prior to the 39th IUPAC General Assembly held at Geneva (Switzerland) in 1997 and is presented here as a companion paper to the Atomic Weights of the Elements 1997. REFERENCES 1. N.E. Holden, R.L. Martin and I.L. Barnes, Pure Appl. Chem., 55, 1119-1136 (1983). 2. N.E. Holden, R.L. Martin and I.L. Barnes, Pure Appl. Chem., 56, 675-694 (1984). 3. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 63, 991-1002 (1991). 4. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 55, 1101-1118 (1983). 5. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 56, 653-674 (1984). 6. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 63, 975-990 (1991)

THE TABLE OF ISOTOPIC COMPOSITIONS OF THE ELEMENTS AS DETERMINED BY MASS SPECTROMETRY The Subcommittee for Isotopic Abundance Measurements(SiAM) has examined the literature available to it through July 1997 and has evaluated these data to produce a table of recommended isotopic abundances for the elements. The table is intended to include values for normal terrestrial samples and does not include values published for meteoritic or other extra-terrestrial materials The column contents are as follows: Column I: The elements are tabulated in ascending order of their atomic numbers Column 2: The symbols for the elements are listed using the abbreviations recommended by IUPac Column 3: The mass number for each isotope is listed Column 4: Range of natural variations Given are the highest and lowest abundances published for each isotope from measurements which have been accepted by the Subcommittee. No data are given in this Column unless a range has been reliably established. The limits given do not include certain exceptional samples, these are noted with a"g"in Column 5 Column 5: Annotations The letters appended in this Column have the following significance g geologically exceptional specimens are known in which the element has an isotopic composition outside the reported range (refers to column 4 m modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the isotopic compositions given can occur. (refers to column 9) r range in isotopic composition existing in normal terrestrial material limits the precision of the isotopic abundances (refers to column 9) Column 6: The best measurement from a single terrestrial source The values are reproduced from the original literature. The uncertainties on the last digits are given in parenthesis as reported in the original publication. As they are not reported in any uniform manner in the literature. SIAM indicates this as follows: Is 2s. 3s indicates 1. 2 or 3 standard deviations, P indicates some other error as defined by the author, and indicates standard error(standard deviation of the mean). Where data are published as isotopic ratios, they, including their uncertainties, are converted to abundances using orthodox procedures C"is appended when calibrated mixtures have been used to correct the mass spectrometer for bias, giving an"absolute"result within the errors stated in the original publication

THE TABLE OF ISOTOPIC COMPOSITIONS OF THE ELEMENTS AS DETERMINED BY MASS SPECTROMETRY The Subcommittee for Isotopic Abundance Measurements (SIAM) has examined the literature available to it through July l997 and has evaluated these data to produce a table of recommended isotopic abundances for the elements. The table is intended to include values for normal terrestrial samples and does not include values published for meteoritic or other extra-terrestrial materials. The column contents are as follows: Column l: The elements are tabulated in ascending order of their atomic numbers. Column 2: The symbols for the elements are listed using the abbreviations recommended by IUPAC. Column 3: The mass number for each isotope is listed. Column 4: Range of natural variations. Given are the highest and lowest abundances published for each isotope from measurements which have been accepted by the Subcommittee. No data are given in this Column unless a range has been reliably established. The limits given do not include certain exceptional samples, these are noted with a "g" in Column 5. Column 5: Annotations The letters appended in this Column have the following significance: g geologically exceptional specimens are known in which the element has an isotopic composition outside the reported range. (refers to column 4) m modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the isotopic compositions given can occur. (refers to column 9) r range in isotopic composition existing in normal terrestrial material limits the precision of the isotopic abundances. (refers to column 9) Column 6: The best measurement from a single terrestrial source. The values are reproduced from the original literature. The uncertainties on the last digits are given in parenthesis as reported in the original publication. As they are not reported in any uniform manner in the literature, SIAM indicates this as follows: ls, 2s, 3s indicates l, 2, or 3 standard deviations, P indicates some other error as defined by the author, and ¢se¢ indicates standard error (standard deviation of the mean). Where data are published as isotopic ratios, they, including their uncertainties, are converted to abundances using orthodox procedures. "C" is appended when calibrated mixtures have been used to correct the mass spectrometer for bias, giving an "absolute" result within the errors stated in the original publication

L"is appended when the linearity of the mass spectrometer has been established for the relevant abundance ratios by using synthetic mixtures of isotopes or certified materials produced by an appropriate Standards laborator N"is appended when none of the above requirements are met The user is cautioned that a)Since the data are reproduced from the literature, the sum of the isotopic abundances may not equal 100 percent b)When a range of compositions has been established, the samples used for the best measurement may come from any part of the range c)An uncalibrated"Best Measurement"is not necessarily free of systematic errors Column 7: The reference shown is that from which the data shown in column 6 were taken(Appendix A Column 8: Reference materials or samples with normal terrestrial isotopic values which are known to be available are listed. An asterisk indicates the reference material used for the best measurement. When additional reference materials are available. the distributors are listed in lieu of specific reference materials(Appendix B) Column 9: Representative Isotopic Composition In this column are listed the values which, in the opinion of SIAM, represent the isotopic composition of the chemicals and/or materials most commonly encountered in the laboratory They may not, therefore, correspond to the most abundant natural material. For example, in the case of hydrogen, the deuterium abundance quoted corresponds to that in fresh water in temperate climates rather than to ocean water. The uncertainties listed in parenthesis cover the range of probable variations of the materials as well as experimental errors. The number of significant figures is chosen to be consistent with the uncertainties, which in turn are derived by applying the statistical guidelines SIAM uses for assigning uncertainties to published isotope abundance measurements. An Atomic Weight calculated from these abundances will be consistent with A(E)values listed in the Table of Standard Atomic Weights 1997 Warning 1)Values in column 9 should be used to determine the average properties of material of unspecified natural terrestrial origin, though no actual sample having the exact composition listed may be 2)When precise work is to be undertaken, such as assessment of individual properties, samples with more precisely known isotopic abundances(such as those listed in column 8)should be obtained or suitable measurements should be made

"L" is appended when the linearity of the mass spectrometer has been established for the relevant abundance ratios by using synthetic mixtures of isotopes or certified materials produced by an appropriate Standards laboratory. "N" is appended when none of the above requirements are met. The user is cautioned that: a) Since the data are reproduced from the literature, the sum of the isotopic abundances may not equal l00 percent. b) When a range of compositions has been established, the samples used for the best measurement may come from any part of the range. c) An uncalibrated "Best Measurement" is not necessarily free of systematic errors. Column 7: The reference shown is that from which the data shown in column 6 were taken (Appendix A). Column 8: Reference materials or samples with normal terrestrial isotopic values which are known to be available are listed. An asterisk indicates the reference material used for the best measurement. When additional reference materials are available, the distributors are listed in lieu of specific reference materials (Appendix B). Column 9: Representative Isotopic Composition. In this column are listed the values which, in the opinion of SIAM, represent the isotopic composition of the chemicals and/or materials most commonly encountered in the laboratory. They may not, therefore, correspond to the most abundant natural material. For example, in the case of hydrogen, the deuterium abundance quoted corresponds to that in fresh water in temperate climates rather than to ocean water. The uncertainties listed in parenthesis cover the range of probable variations of the materials as well as experimental errors. The number of significant figures is chosen to be consistent with the uncertainties, which in turn are derived by applying the statistical guidelines SIAM uses for assigning uncertainties to published isotope abundance measurements. An Atomic Weight calculated from these abundances will be consistent with Ar(E) values listed in the Table of Standard Atomic Weights 1997. Warning 1) Values in column 9 should be used to determine the average properties of material of unspecified natural terrestrial origin, though no actual sample having the exact composition listed may be available. 2) When precise work is to be undertaken, such as assessment of individual properties, samples with more precisely known isotopic abundances (such as those listed in column 8) should be obtained or suitable measurements should be made