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Capabilities of inductively coupled plasma mass spectrometry for the measurement of Fe isotope ratios

Frank Vanhaecke UGent, Lieve Balcaen UGent, Günther De Wannemacker and Luc Moens UGent (2002) JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY. 17(8). p.933-943
abstract
Reliable isotopic analysis of Fe by means of inductively coupled plasma mass spectrometry (ICP-MS) is traditionally hindered by spectral overlap of the analyte signals with those of Ar- and Ca-based molecular ions. The merits of several approaches for overcoming spectral interferences-operation of the ICP under cool plasma conditions, membrane desolvation of the sample aerosol, use of a double-focusing sector field mass spectrometer operated at a higher mass resolution and ion-molecule chemistry in a dynamic reaction cell (DRC)-for solving this particular problem were critically compared and the most successful approaches were subsequently used for the determination of Fe isotope ratios in a human serum reference material. Although beneficial to some extent and/or for some of the Fe nuclides, cool plasma conditions and membrane desolvation were shown to offer no sufficient reduction in the intensity of the interfering ions. With DRC-ICP-MS, all reaction gases tested, NH3, CO and N-2, showed a similar behaviour. An excellent performance in terms of both freedom from spectral overlap and isotope ratio precision, not exceeding the theoretical precision calculated on the basis of counting statistics and less than or equal to0.2% RSD for 5 successive measurements, was established for aqueous standard solutions. In the presence of Ca, however, the detrimental influence of spectral interferences precluded accurate determination of Fe-57/Fe-56 at the standard RPq setting. When using a matrix-matched blank in addition to CO as a reaction gas to correct for the remaining overlap, Fe-54/Fe-56 could, however, be accurately and precisely measured in human serum. It was established that, with DRC-ICP-MS, the matrix composition affected the mass discrimination to a significant extent, such that the isotopic standard used for mass discrimination also required matrix-matching. Further optimisation of the RPq value resulted in an improved signal-to-background ratio at a mass-to-charge ratio of 57. Despite a marked increase in mass discrimination, Fe-54/Fe-56 could still be accurately determined under these conditions (deviation from true value <0.1%) while the result for Fe-57/Fe-56 was substantially improved. The total uncertainty on a single determination (5 replicate measurements of 60 s each) of the Fe-54/Fe-56 ratio typically amounted to approximately 0.5%. When using sector field ICP-MS operated at a mass resolution of 3000, the analyte signals could be resolved from those of the above-mentioned molecular ions. For aqueous standard solutions, the isotope ratio precision attainable with sector field ICP-MS, typically 0.2-0.4% for Fe-54/Fe-56 and Fe-57/Fe-56 and &GE;1% for Fe-58/Fe-56, was significantly worse than that obtained with DRC-ICP-MS. The deviation between the experimental values for Fe-54/Fe-56 and Fe-57/Fe-56 in human serum and the corresponding true values, however, was <0.05%, while the total uncertainty on the ICP-MS results was approximately 0.5% (5 replicate measurements of 90 s each). Due to the low isotopic abundance of Fe-58, the uncertainty for Fe-58/Fe-56 deteriorated to similar to2.5%. Conclusions concerning the applicability of ICP-MS for isotopic analysis of Fe are presented and some ideas for further research are discussed.
Please use this url to cite or link to this publication:
author
organization
year
type
journalArticle (original)
publication status
published
subject
keyword
RESOLUTION, ABSORPTION, IRON, HUMAN-SERUM, DYNAMIC REACTION CELL, REACTION CHEMISTRY, TRACE-ELEMENTS, ICP-MS, ISOBARIC INTERFERENCES, PRECISION
journal title
JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY
J. Anal. At. Spectrom.
volume
17
issue
8
pages
933 - 943
Web of Science type
Article
Web of Science id
000177254600029
JCR category
CHEMISTRY, ANALYTICAL
JCR impact factor
4.25 (2002)
JCR rank
4/67 (2002)
JCR quartile
1 (2002)
ISSN
0267-9477
DOI
10.1039/b202409h
language
English
UGent publication?
yes
classification
A1
id
162694
handle
http://hdl.handle.net/1854/LU-162694
date created
2004-01-14 13:39:00
date last changed
2012-11-14 10:51:47
@article{162694,
  abstract     = {Reliable isotopic analysis of Fe by means of inductively coupled plasma mass spectrometry (ICP-MS) is traditionally hindered by spectral overlap of the analyte signals with those of Ar- and Ca-based molecular ions. The merits of several approaches for overcoming spectral interferences-operation of the ICP under cool plasma conditions, membrane desolvation of the sample aerosol, use of a double-focusing sector field mass spectrometer operated at a higher mass resolution and ion-molecule chemistry in a dynamic reaction cell (DRC)-for solving this particular problem were critically compared and the most successful approaches were subsequently used for the determination of Fe isotope ratios in a human serum reference material. Although beneficial to some extent and/or for some of the Fe nuclides, cool plasma conditions and membrane desolvation were shown to offer no sufficient reduction in the intensity of the interfering ions. With DRC-ICP-MS, all reaction gases tested, NH3, CO and N-2, showed a similar behaviour. An excellent performance in terms of both freedom from spectral overlap and isotope ratio precision, not exceeding the theoretical precision calculated on the basis of counting statistics and less than or equal to0.2\% RSD for 5 successive measurements, was established for aqueous standard solutions. In the presence of Ca, however, the detrimental influence of spectral interferences precluded accurate determination of Fe-57/Fe-56 at the standard RPq setting. When using a matrix-matched blank in addition to CO as a reaction gas to correct for the remaining overlap, Fe-54/Fe-56 could, however, be accurately and precisely measured in human serum. It was established that, with DRC-ICP-MS, the matrix composition affected the mass discrimination to a significant extent, such that the isotopic standard used for mass discrimination also required matrix-matching. Further optimisation of the RPq value resulted in an improved signal-to-background ratio at a mass-to-charge ratio of 57. Despite a marked increase in mass discrimination, Fe-54/Fe-56 could still be accurately determined under these conditions (deviation from true value {\textlangle}0.1\%) while the result for Fe-57/Fe-56 was substantially improved. The total uncertainty on a single determination (5 replicate measurements of 60 s each) of the Fe-54/Fe-56 ratio typically amounted to approximately 0.5\%. When using sector field ICP-MS operated at a mass resolution of 3000, the analyte signals could be resolved from those of the above-mentioned molecular ions. For aqueous standard solutions, the isotope ratio precision attainable with sector field ICP-MS, typically 0.2-0.4\% for Fe-54/Fe-56 and Fe-57/Fe-56 and \&GE;1\% for Fe-58/Fe-56, was significantly worse than that obtained with DRC-ICP-MS. The deviation between the experimental values for Fe-54/Fe-56 and Fe-57/Fe-56 in human serum and the corresponding true values, however, was {\textlangle}0.05\%, while the total uncertainty on the ICP-MS results was approximately 0.5\% (5 replicate measurements of 90 s each). Due to the low isotopic abundance of Fe-58, the uncertainty for Fe-58/Fe-56 deteriorated to similar to2.5\%. Conclusions concerning the applicability of ICP-MS for isotopic analysis of Fe are presented and some ideas for further research are discussed.},
  author       = {Vanhaecke, Frank and Balcaen, Lieve and De Wannemacker, G{\"u}nther and Moens, Luc},
  issn         = {0267-9477},
  journal      = {JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY},
  keyword      = {RESOLUTION,ABSORPTION,IRON,HUMAN-SERUM,DYNAMIC REACTION CELL,REACTION CHEMISTRY,TRACE-ELEMENTS,ICP-MS,ISOBARIC INTERFERENCES,PRECISION},
  language     = {eng},
  number       = {8},
  pages        = {933--943},
  title        = {Capabilities of inductively coupled plasma mass spectrometry for the measurement of Fe isotope ratios},
  url          = {http://dx.doi.org/10.1039/b202409h},
  volume       = {17},
  year         = {2002},
}

Chicago
Vanhaecke, Frank, Lieve Balcaen, Günther De Wannemacker, and Luc Moens. 2002. “Capabilities of Inductively Coupled Plasma Mass Spectrometry for the Measurement of Fe Isotope Ratios.” Journal of Analytical Atomic Spectrometry 17 (8): 933–943.
APA
Vanhaecke, Frank, Balcaen, L., De Wannemacker, G., & Moens, L. (2002). Capabilities of inductively coupled plasma mass spectrometry for the measurement of Fe isotope ratios. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, 17(8), 933–943.
Vancouver
1.
Vanhaecke F, Balcaen L, De Wannemacker G, Moens L. Capabilities of inductively coupled plasma mass spectrometry for the measurement of Fe isotope ratios. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY. 2002;17(8):933–43.
MLA
Vanhaecke, Frank, Lieve Balcaen, Günther De Wannemacker, et al. “Capabilities of Inductively Coupled Plasma Mass Spectrometry for the Measurement of Fe Isotope Ratios.” JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 17.8 (2002): 933–943. Print.