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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.


Relative contributions to thestandard uncertainty of the determination of metal mass concentration inambient air, as part of the UK Heavy Metals Monitoring Network. This exampleshows a measurement with an overall expanded uncertainty at the 95% confidenceinterval of approximately 20%. The changing uncertainty contribution from thevariation in the sample isotopic composition for the different metals measuredby the “network” is indicated by the additional lines and labelling on thebottom bar.
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Related In: Results  -  Collection


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fig1: Relative contributions to thestandard uncertainty of the determination of metal mass concentration inambient air, as part of the UK Heavy Metals Monitoring Network. This exampleshows a measurement with an overall expanded uncertainty at the 95% confidenceinterval of approximately 20%. The changing uncertainty contribution from thevariation in the sample isotopic composition for the different metals measuredby the “network” is indicated by the additional lines and labelling on thebottom bar.

Mentions: Rather than assess theisotopic composition of each individual sample, the uncertainty budgetdeveloped for this measurement includes a component of uncertainty to recognisethat the isotopic composition of the sample may fall anywhere within the rangeof natural variations, or the representative isotopic composition, whichever isthe larger range [17]. (The actual range of isotopiccomposition in environmental samples may be considerably narrower [18].)In practice, this assumption assigns δX = 1 but imposes a relative uncertainty on thisvalue equal to the possible range of isotope abundances expected for theisotopes used for quantification. Relatively little detail exists in theliterature on the isotopic composition of metals in ambient air particulates. The vast majority of the work that has been published has been on Pb isotopiccomposition, where the greatest variation is expected. Determination of isotoperatios has been mostly used as a route to determining the origin of the Pbsampled, particularly with regard to specific industrial processes orlong-range pollutant transport [14]. One study [19]has examined the Pb isotopic composition in deposition in order to compare howthis changed before and after the closure of a local Pb mine. Others studies [20, 21]have used the changing Pb isotope ratios in ambient particulate matter todemonstrate the seasonal variation long-range transport of pollutants acrossthe Asian continent. Measured Pb isotope ratios have also been used as a routeto determine the changing origins of Pb emissions in an urban environmentduring and after the phasing out of leaded petrol [22]. Cu and Zn isotopes ratios have been analysed near a large Zn refinery [23]as a means of determining the origin of metallic ores, and Sr and Nd isotoperatios have been used in the discrimination of emissions from variousindustrial sources and traffic emissions, respectively [24]. In all cases, the observed ranges of the isotopic compositions fell well withinthe natural ranges predicted [17] and these natural ranges have been used to constructthe uncertainty budget presented in this paper. Moreover, when the isotopiccomposition of samples under consideration in this study has been measuredperiodically, the abundance of the isotope used for quantitation has alwaysbeen well within these ranges as well [25]. The major contributions to the overall measurement uncertainty for thedetermination of the mass concentration of metal in ambient air are shown inFigure 1.


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)

Relative contributions to thestandard uncertainty of the determination of metal mass concentration inambient air, as part of the UK Heavy Metals Monitoring Network. This exampleshows a measurement with an overall expanded uncertainty at the 95% confidenceinterval of approximately 20%. The changing uncertainty contribution from thevariation in the sample isotopic composition for the different metals measuredby the “network” is indicated by the additional lines and labelling on thebottom bar.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2637369&req=5

fig1: Relative contributions to thestandard uncertainty of the determination of metal mass concentration inambient air, as part of the UK Heavy Metals Monitoring Network. This exampleshows a measurement with an overall expanded uncertainty at the 95% confidenceinterval of approximately 20%. The changing uncertainty contribution from thevariation in the sample isotopic composition for the different metals measuredby the “network” is indicated by the additional lines and labelling on thebottom bar.
Mentions: Rather than assess theisotopic composition of each individual sample, the uncertainty budgetdeveloped for this measurement includes a component of uncertainty to recognisethat the isotopic composition of the sample may fall anywhere within the rangeof natural variations, or the representative isotopic composition, whichever isthe larger range [17]. (The actual range of isotopiccomposition in environmental samples may be considerably narrower [18].)In practice, this assumption assigns δX = 1 but imposes a relative uncertainty on thisvalue equal to the possible range of isotope abundances expected for theisotopes used for quantification. Relatively little detail exists in theliterature on the isotopic composition of metals in ambient air particulates. The vast majority of the work that has been published has been on Pb isotopiccomposition, where the greatest variation is expected. Determination of isotoperatios has been mostly used as a route to determining the origin of the Pbsampled, particularly with regard to specific industrial processes orlong-range pollutant transport [14]. One study [19]has examined the Pb isotopic composition in deposition in order to compare howthis changed before and after the closure of a local Pb mine. Others studies [20, 21]have used the changing Pb isotope ratios in ambient particulate matter todemonstrate the seasonal variation long-range transport of pollutants acrossthe Asian continent. Measured Pb isotope ratios have also been used as a routeto determine the changing origins of Pb emissions in an urban environmentduring and after the phasing out of leaded petrol [22]. Cu and Zn isotopes ratios have been analysed near a large Zn refinery [23]as a means of determining the origin of metallic ores, and Sr and Nd isotoperatios have been used in the discrimination of emissions from variousindustrial sources and traffic emissions, respectively [24]. In all cases, the observed ranges of the isotopic compositions fell well withinthe natural ranges predicted [17] and these natural ranges have been used to constructthe uncertainty budget presented in this paper. Moreover, when the isotopiccomposition of samples under consideration in this study has been measuredperiodically, the abundance of the isotope used for quantitation has alwaysbeen well within these ranges as well [25]. The major contributions to the overall measurement uncertainty for thedetermination of the mass concentration of metal in ambient air are shown inFigure 1.

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.