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 |
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Authors: | James Chung Wah Lam Yiu Chung Yip Wai Fong Tong |
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Institution: | (1) Government Laboratory, Ho Man Tin Government Offices, 88 Chung Hau Street, Kowloon, Hong Kong SAR, People’s Republic of China |
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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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Keywords: | Q-ICP-MS ID-ICP-MS Precision Lead isotope ratios Uncertainty |
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