Important warning about the uncertainties affecting results of dissolved iron concentration measurements in seawater using flow-injection with chemiluminescence detection

Flow-Injection with Chemiluminescence (FI-CL) is a procedure commonly applied in the framework of the GEOTRACES cruises because of its portability and hence suitability for shipboard deployment.

Following the Guide for Uncertainty Measurement (GUM) approach, Floor and colleagues propose dedicated mathematical equations allowing the estimation of measurement uncertainties. They apply their model to estimate combined uncertainties obtained for analyses of seawater reference materials (SAFe and GEOTRACES).

This thorough and rigorous examination shows that the final uncertainty of the measurement results using FI-CL in the present protocol configuration cannot be better than 10–15% for seawater samples containing 0.5–1 nmol/kg of dissolved iron (Fe).

This uncertainty might be larger at sea, under more challenging conditions. The most influential sources of uncertainty are the uncertainty on the calibration slope and the lack of stability during the analytical sequence, see figures below).

Authors clearly consider that uncertainty estimations based on the intensity repeatability alone, as is often done in FI-CL studies, is not a realistic estimation of the overall uncertainty of the measurement procedure.

16 Floor l
Figures: Combined uncertainty budget estimated for measurements corresponding to signal peak height integration (left, rel. U = 12%, k = 2)
and to signal peak area integration (right, rel. U = 10%, k = 2). Click here to download the figures.

Reference:

Floor, G. H., Clough, R., Lohan, M. C., Ussher, S. J., Worsfold, P. J. and Quétel, C. R. (2015), Combined uncertainty estimation for the determination of the dissolved iron amount content in seawater using flow injection with chemiluminescence detection. Limnol. Oceanogr. Methods, 13: 673–686. doi:10.1002/lom3.10057

Latest highlights

Science Highlights

Loss of old Arctic sea ice increases methylmercury concentrations

Researchers from the SCRIPPS, the Stockholm Natural Museum and the Mediterranean Institute of Oceanography show the importance of sea ice composition on methylmercury budgets

02.09.2020

Science Highlights

Estimating Atmospheric Trace Element Deposition Over the Global Ocean

A recently developed method based on the natural radionuclide Be-7 has provided a means to estimate the bulk atmospheric trace element deposition velocity

Science Highlights

Dissolved gallium unravels Pacific and Atlantic waters in the Arctic Ocean

Whitmore and co-workers demonstrate that the dissolved gallium distribution provide a better water source deconvolution than the nutrient tracers

22.07.2020

Science Highlights

Precise estimate of the mercury export from the Arctic to the Atlantic Ocean

Using new observations acquired during GEOTRACES Arctic cruises, a refined arctic mercury budget has been established

21.07.2020

Rechercher