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Uncertainty evaluation of the diffusive gradients in thin films technique.

Kreuzeder A, Santner J, Zhang H, Prohaska T, Wenzel WW - Environ. Sci. Technol. (2015)

Bottom Line: While several factors considerably contribute to the uncertainty of bulk DGT, the uncertainty of DGT LA-ICP-MS mainly depends on the signal variability of the ablation analysis.The combined uncertainties determined in this study support the use of DGT as a monitoring instrument.It is expected that the analytical requirements of legal frameworks, for example, the EU Drinking Water Directive, are met by DGT sampling.

View Article: PubMed Central - PubMed

Affiliation: University of Natural Resources and Life Sciences, Vienna , Department of Forest and Soil Sciences, Institute of Soil Research, Konrad-Lorenz-Strasse 24, 3430 Tulln, Austria.

ABSTRACT
Although the analytical performance of the diffusive gradients in thin films (DGT) technique is well investigated, there is no systematic analysis of the DGT measurement uncertainty and its sources. In this study we determine the uncertainties of bulk DGT measurements (not considering labile complexes) and of DGT-based chemical imaging using laser ablation - inductively coupled plasma mass spectrometry. We show that under well-controlled experimental conditions the relative combined uncertainties of bulk DGT measurements are ∼10% at a confidence interval of 95%. While several factors considerably contribute to the uncertainty of bulk DGT, the uncertainty of DGT LA-ICP-MS mainly depends on the signal variability of the ablation analysis. The combined uncertainties determined in this study support the use of DGT as a monitoring instrument. It is expected that the analytical requirements of legal frameworks, for example, the EU Drinking Water Directive, are met by DGT sampling.

No MeSH data available.


Related in: MedlinePlus

Relative uncertainty(k = 2) plotted against increasing cDGT values for P (lower axis) and eluate concentration(top axis) in a 12 h deployment in a cDGT-range from 1.3 μg L–1 to 242 μg L–1 (Δgdl = 0.093 cm, D (P) = 6.01 × 10–6 cm2 s–1).
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fig1: Relative uncertainty(k = 2) plotted against increasing cDGT values for P (lower axis) and eluate concentration(top axis) in a 12 h deployment in a cDGT-range from 1.3 μg L–1 to 242 μg L–1 (Δgdl = 0.093 cm, D (P) = 6.01 × 10–6 cm2 s–1).

Mentions: Figure 1 shows that theeluate concentration strongly influences the uncertainty of a DGTmeasurement. The relative uncertainty for a cDGT value of 1.3 μg L–1 P is 41.2%(k = 2) while this uncertainty sharply decreasesto 8.2% at a cDGT value of 13.3 μgL–1 P and further slowly decreases to 7.2% at a cDGT-concentration of 242 μg L–1 of P. An extreme example is a cDGT-valueof 1.7 μg L–1 Cd resulting in a relative uncertaintyof 80.2% while at a cDGT-concentrationof 470 μg L–1 Cd the uncertainty is 7.9% (k = 2, Table 2). In this case theuncertainty of the intercept of the calibration curve contributesexcessively to the combined uncertainty. When measurements are performedat low eluate concentrations, the major contributors to the uncertaintyare predominantly the calibration parameters, especially the uncertaintyof the intercept (bcal). At elevated concentrationsthe major contributors are fe and Dgel, resulting in relative uncertainties of7.0–12.9% (k = 2, Table 2). This clearly illustrates, that measurements of eluate concentrationsclose to the PQL lead to increased uncertainties. In such cases theuncertainty could be considerably reduced by increasing the eluateconcentration, for example, by using longer DGT deployment times,by the use of a thinner diffusion layer or by using smaller eluatevolumes. Furthermore, a change in analytical instrumentation, e.g.,P measurement on an ICP-MS instrument instead of a photometer, canlead to better sensitivities and lower LODs.


Uncertainty evaluation of the diffusive gradients in thin films technique.

Kreuzeder A, Santner J, Zhang H, Prohaska T, Wenzel WW - Environ. Sci. Technol. (2015)

Relative uncertainty(k = 2) plotted against increasing cDGT values for P (lower axis) and eluate concentration(top axis) in a 12 h deployment in a cDGT-range from 1.3 μg L–1 to 242 μg L–1 (Δgdl = 0.093 cm, D (P) = 6.01 × 10–6 cm2 s–1).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4319404&req=5

fig1: Relative uncertainty(k = 2) plotted against increasing cDGT values for P (lower axis) and eluate concentration(top axis) in a 12 h deployment in a cDGT-range from 1.3 μg L–1 to 242 μg L–1 (Δgdl = 0.093 cm, D (P) = 6.01 × 10–6 cm2 s–1).
Mentions: Figure 1 shows that theeluate concentration strongly influences the uncertainty of a DGTmeasurement. The relative uncertainty for a cDGT value of 1.3 μg L–1 P is 41.2%(k = 2) while this uncertainty sharply decreasesto 8.2% at a cDGT value of 13.3 μgL–1 P and further slowly decreases to 7.2% at a cDGT-concentration of 242 μg L–1 of P. An extreme example is a cDGT-valueof 1.7 μg L–1 Cd resulting in a relative uncertaintyof 80.2% while at a cDGT-concentrationof 470 μg L–1 Cd the uncertainty is 7.9% (k = 2, Table 2). In this case theuncertainty of the intercept of the calibration curve contributesexcessively to the combined uncertainty. When measurements are performedat low eluate concentrations, the major contributors to the uncertaintyare predominantly the calibration parameters, especially the uncertaintyof the intercept (bcal). At elevated concentrationsthe major contributors are fe and Dgel, resulting in relative uncertainties of7.0–12.9% (k = 2, Table 2). This clearly illustrates, that measurements of eluate concentrationsclose to the PQL lead to increased uncertainties. In such cases theuncertainty could be considerably reduced by increasing the eluateconcentration, for example, by using longer DGT deployment times,by the use of a thinner diffusion layer or by using smaller eluatevolumes. Furthermore, a change in analytical instrumentation, e.g.,P measurement on an ICP-MS instrument instead of a photometer, canlead to better sensitivities and lower LODs.

Bottom Line: While several factors considerably contribute to the uncertainty of bulk DGT, the uncertainty of DGT LA-ICP-MS mainly depends on the signal variability of the ablation analysis.The combined uncertainties determined in this study support the use of DGT as a monitoring instrument.It is expected that the analytical requirements of legal frameworks, for example, the EU Drinking Water Directive, are met by DGT sampling.

View Article: PubMed Central - PubMed

Affiliation: University of Natural Resources and Life Sciences, Vienna , Department of Forest and Soil Sciences, Institute of Soil Research, Konrad-Lorenz-Strasse 24, 3430 Tulln, Austria.

ABSTRACT
Although the analytical performance of the diffusive gradients in thin films (DGT) technique is well investigated, there is no systematic analysis of the DGT measurement uncertainty and its sources. In this study we determine the uncertainties of bulk DGT measurements (not considering labile complexes) and of DGT-based chemical imaging using laser ablation - inductively coupled plasma mass spectrometry. We show that under well-controlled experimental conditions the relative combined uncertainties of bulk DGT measurements are ∼10% at a confidence interval of 95%. While several factors considerably contribute to the uncertainty of bulk DGT, the uncertainty of DGT LA-ICP-MS mainly depends on the signal variability of the ablation analysis. The combined uncertainties determined in this study support the use of DGT as a monitoring instrument. It is expected that the analytical requirements of legal frameworks, for example, the EU Drinking Water Directive, are met by DGT sampling.

No MeSH data available.


Related in: MedlinePlus