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The effect of isotopic composition on the uncertainty of routine metal mass concentration measurements in ambient air.

Brown RJ, Goddard SL, Brown AS, Yardley RE - J Autom Methods Manag Chem (2009)

Bottom Line: It is observed that the uncertainty contribution from possible variation in the isotopic composition of the sample depends on the element in question, but can be significant (e.g., for Pb, Cd, and Hg).Therefore, in order to confirm the validity of this quantification methodology and its uncertainty budget, the isotopic composition of the calibration standards used for quantification has been determined.The results of this analysis are presented here.

View Article: PubMed Central - PubMed

Affiliation: Analytical Science Team, National Physical Laboratory, Teddington, Middlesex TW11 0LW, UK.

ABSTRACT
The main sources of uncertainty encountered during the analysis of the mass concentration of metals in ambient air as part of the operation of the UK Heavy Metals Monitoring Network are presented. It is observed that the uncertainty contribution from possible variation in the isotopic composition of the sample depends on the element in question, but can be significant (e.g., for Pb, Cd, and Hg). The working curve method for the ICP-MS analysis of metals in solution, with a low resolution, high throughput instrument measuring at one m/z ratio per element, relies on the relative abundance of the isotopes under consideration being the same in both the sample and the calibration solution. Calculation of the uncertainty in this analysis assumes that the isotopic composition variation within the sample and calibration solution is limited to a defined range. Therefore, in order to confirm the validity of this quantification methodology and its uncertainty budget, the isotopic composition of the calibration standards used for quantification has been determined. The results of this analysis are presented here.

No MeSH data available.


(a) V, Cr, Fe, Ni, Cu, and Zn: comparison ofthe measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass number isdisplayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart. (b) Cd, Pt, Hg, and Pb: comparisonof the measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass numberis displayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart.
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fig3: (a) V, Cr, Fe, Ni, Cu, and Zn: comparison ofthe measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass number isdisplayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart. (b) Cd, Pt, Hg, and Pb: comparisonof the measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass numberis displayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart.

Mentions: The summary uncertainty budgetpresented in Figures 1 and 2 (and the measurement equation from which this hasbeen developed) is only valid if the abundance of the isotope used forquantification in the calibration standards also falls within this rangeallowed for the samples. If it does not,then an additional uncertainty contribution, or a correction factor, may needto be applied. This is not something that may be taken for granted since thecalibration standards may often have been prepared from isotopically enrichedpure materials, and must be measured in order to determine whether an increasein the uncertainty estimate for the overall determination was required. Theresults of the determination of the isotopic composition of the calibrationstandards used are shown in Figures 3(a) and 3(b) which show that the majorityof isotopes demonstrated good agreement between the measured value and theexpected range of isotopic abundances. Table 1 highlights the level of thisagreement for the isotopes used for quantification.


The effect of isotopic composition on the uncertainty of routine metal mass concentration measurements in ambient air.

Brown RJ, Goddard SL, Brown AS, Yardley RE - J Autom Methods Manag Chem (2009)

(a) V, Cr, Fe, Ni, Cu, and Zn: comparison ofthe measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass number isdisplayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart. (b) Cd, Pt, Hg, and Pb: comparisonof the measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass numberis displayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2637369&req=5

fig3: (a) V, Cr, Fe, Ni, Cu, and Zn: comparison ofthe measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass number isdisplayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart. (b) Cd, Pt, Hg, and Pb: comparisonof the measured relative isotopic abundance of the calibration standards (blackcircles, with the grey bars representing the standard error of the mean)against the expected range in natural, or representative, isotopic compositions(whichever is the larger range) (black bars). The relative atomic mass numberis displayed for each isotope, with the boxed number being the isotope used forthe quantification of the samples. Values are normalised to the centre of thenatural (or representative) composition range for each isotope. The relativeabundance is displayed for each element in the separate plot beneath the mainchart.
Mentions: The summary uncertainty budgetpresented in Figures 1 and 2 (and the measurement equation from which this hasbeen developed) is only valid if the abundance of the isotope used forquantification in the calibration standards also falls within this rangeallowed for the samples. If it does not,then an additional uncertainty contribution, or a correction factor, may needto be applied. This is not something that may be taken for granted since thecalibration standards may often have been prepared from isotopically enrichedpure materials, and must be measured in order to determine whether an increasein the uncertainty estimate for the overall determination was required. Theresults of the determination of the isotopic composition of the calibrationstandards used are shown in Figures 3(a) and 3(b) which show that the majorityof isotopes demonstrated good agreement between the measured value and theexpected range of isotopic abundances. Table 1 highlights the level of thisagreement for the isotopes used for quantification.

Bottom Line: It is observed that the uncertainty contribution from possible variation in the isotopic composition of the sample depends on the element in question, but can be significant (e.g., for Pb, Cd, and Hg).Therefore, in order to confirm the validity of this quantification methodology and its uncertainty budget, the isotopic composition of the calibration standards used for quantification has been determined.The results of this analysis are presented here.

View Article: PubMed Central - PubMed

Affiliation: Analytical Science Team, National Physical Laboratory, Teddington, Middlesex TW11 0LW, UK.

ABSTRACT
The main sources of uncertainty encountered during the analysis of the mass concentration of metals in ambient air as part of the operation of the UK Heavy Metals Monitoring Network are presented. It is observed that the uncertainty contribution from possible variation in the isotopic composition of the sample depends on the element in question, but can be significant (e.g., for Pb, Cd, and Hg). The working curve method for the ICP-MS analysis of metals in solution, with a low resolution, high throughput instrument measuring at one m/z ratio per element, relies on the relative abundance of the isotopes under consideration being the same in both the sample and the calibration solution. Calculation of the uncertainty in this analysis assumes that the isotopic composition variation within the sample and calibration solution is limited to a defined range. Therefore, in order to confirm the validity of this quantification methodology and its uncertainty budget, the isotopic composition of the calibration standards used for quantification has been determined. The results of this analysis are presented here.

No MeSH data available.