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Evaluating the precision of Pb isotope measurement by mass spectrometry

Evaluating the precision of Pb isotope measurement by mass spectrometry
Evaluating the precision of Pb isotope measurement by mass spectrometry
Analytical precision for Pb isotope measurement by thermal and plasma source mass spectrometry has improved by an order of magnitude in the last 20 years. Much of this improvement relates to a shift away from the external method of correcting instrumental mass fractionation – where samples are assumed to fractionate to the same extent as an average value of a working measurement standard. Implementation of a variety of techniques, including thallium spiking, sample–standard bracketing and double/triple spiking has provided more robust methods of fractionation correction. Isotope laboratories use one or more of these procedures, but an assessment of the measurement precision and relative merits of each system is needed to determine which is the most appropriate for the purpose. This study reviews each of these methods and provides a comparison based on an extensive analytical record covering 18 years, and using a variety of mass spectrometers. As two or three of the methods have been applied to most measurements, direct and robust comparisons can be made between correction protocols. In particular the effects of sample purity and variable sample matrices on measurement precision and accuracy have been examined. Data acquired from the measurement of rock, soil and metal are used to provide a statistical comparison of the analytical uncertainty of each technique, guiding the choice of the most appropriate method. Isotope standard data acquired over this period is also compared with other high-precision laboratories to generate a set of concordant working ratios for the NIST SRM 981 Pb standard: 206Pb/204Pb = 16.9412; 207Pb/204Pb = 15.4988; 208Pb/204Pb = 36.7233.
0267-9477
198-213
Taylor, Rex N.
094be7fd-ef61-4acd-a795-7daba2bc6183
Ishizuka, Osamu
1fb98a88-bff7-4200-a09d-92ddf1616058
Michalik, Agnieszka
f117a40f-0df7-4130-8a18-2b37cad5bbef
Milton, J. Andrew
9e183221-d0d4-4ddb-aeba-0fdde9d31230
Croudace, Ian W.
24deb068-d096-485e-8a23-a32b7a68afaf
Taylor, Rex N.
094be7fd-ef61-4acd-a795-7daba2bc6183
Ishizuka, Osamu
1fb98a88-bff7-4200-a09d-92ddf1616058
Michalik, Agnieszka
f117a40f-0df7-4130-8a18-2b37cad5bbef
Milton, J. Andrew
9e183221-d0d4-4ddb-aeba-0fdde9d31230
Croudace, Ian W.
24deb068-d096-485e-8a23-a32b7a68afaf

Taylor, Rex N., Ishizuka, Osamu, Michalik, Agnieszka, Milton, J. Andrew and Croudace, Ian W. (2015) Evaluating the precision of Pb isotope measurement by mass spectrometry. Journal of Analytical Atomic Spectrometry, 30 (1), 198-213. (doi:10.1039/C4JA00279B).

Record type: Article

Abstract

Analytical precision for Pb isotope measurement by thermal and plasma source mass spectrometry has improved by an order of magnitude in the last 20 years. Much of this improvement relates to a shift away from the external method of correcting instrumental mass fractionation – where samples are assumed to fractionate to the same extent as an average value of a working measurement standard. Implementation of a variety of techniques, including thallium spiking, sample–standard bracketing and double/triple spiking has provided more robust methods of fractionation correction. Isotope laboratories use one or more of these procedures, but an assessment of the measurement precision and relative merits of each system is needed to determine which is the most appropriate for the purpose. This study reviews each of these methods and provides a comparison based on an extensive analytical record covering 18 years, and using a variety of mass spectrometers. As two or three of the methods have been applied to most measurements, direct and robust comparisons can be made between correction protocols. In particular the effects of sample purity and variable sample matrices on measurement precision and accuracy have been examined. Data acquired from the measurement of rock, soil and metal are used to provide a statistical comparison of the analytical uncertainty of each technique, guiding the choice of the most appropriate method. Isotope standard data acquired over this period is also compared with other high-precision laboratories to generate a set of concordant working ratios for the NIST SRM 981 Pb standard: 206Pb/204Pb = 16.9412; 207Pb/204Pb = 15.4988; 208Pb/204Pb = 36.7233.

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More information

e-pub ahead of print date: 3 October 2014
Published date: January 2015
Organisations: Geochemistry

Identifiers

Local EPrints ID: 373267
URI: http://eprints.soton.ac.uk/id/eprint/373267
ISSN: 0267-9477
PURE UUID: 81f154de-0e8d-4960-8aa5-f7121b71f040

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Date deposited: 12 Jan 2015 15:42
Last modified: 24 Oct 2018 16:31

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