Revisiting type-A uncertainties relating to the measurement of mass fraction of lead using isotope-dilution inductively coupled plasma mass spectrometry: a way of improving measurement precision and expanded uncertainty

Abstract

A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) has been used for determination of lead in plant materials using isotope-dilution inductively coupled plasma mass spectrometry. The accuracy of the method was demonstrated by analysis of a matrix certified reference material, NIST SRM 1547 Peach Leaves. Specific instrumental parameters of Q-ICP-MS, including isotope analysis mode, integration time per point, number of points per mass, and number of measurements, were optimized to obtain the best measurement precision. The precision (expressed as relative standard deviation) associated with replicate measurement of the 208Pb/206Pb isotope ratio and its mass-bias correction factor was <0.2%. Following “Example A7” of the Eurachem/CITAC Guide, the relative expanded uncertainty, U rel, (coverage factor k = 2) was found to be ±1.1%, which fulfilled the target value of ±2% maximum and was lower than the uncertainty of ±3.4% reported by NIST based on isotope-dilution thermal ionization mass spectrometry. Sample recovery of 99% was obtained.

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Acknowledgments

The authors are indebted to Dr T.L. Ting (Government Chemist) and Ms S.Y.K. Tam for their encouragement, advice and help. We would like to thank Mr K.K. Chan for laboratory assistance. The contents of this article do not necessarily reflect the views of the Government of the Hong Kong Special Administrative Region, nor does mention of trade names or commercial products constitute endorsement or recommendations of use.

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Correspondence to Wai Fong Tong.

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Lam, J.C.W., Yip, Y.C. & Tong, W.F. Revisiting type-A uncertainties relating to the measurement of mass fraction of lead using isotope-dilution inductively coupled plasma mass spectrometry: a way of improving measurement precision and expanded uncertainty. Accred Qual Assur 13, 311–319 (2008). https://doi.org/10.1007/s00769-008-0384-8

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Keywords

  • Q-ICP-MS
  • ID-ICP-MS
  • Precision
  • Lead isotope ratios
  • Uncertainty