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.


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

Constraining Oceanic Copper Cycling through Artificial Intelligence and Ocean Circulation Inverse Model

Using available observations of dissolved copper, artificial neural networks, and an ocean circulation inverse model, authors calculated a global estimate of the 3-dimensional distribution and cycling of dissolved copper in the ocean


Science Highlights

Particulate rare earth elements distributions, processes and characterisation of nepheloids in the North Atlantic

Lagarde et al. realised the first basin scale section of particulate rare earth elements concentrations across the North Atlantic Ocean.


Science Highlights

Isopycnal mixing controls protactinium and thorium distributions in the Pacific Southern Ocean

Pavia and co-workers determined the physical and chemical speciation as well as the vertical distribution of Protactinium-231 and Thorium-230 at 12 stations across the Southern Pacific Antarctic Circumpolar Current…


Science Highlights

Time series thorium-230 data reveal scavenging intensification over the last 15 years in the Arctic Ocean

Authors demonstrate that the later hypothesis is likely explaining thorium-230-depletion in intermediate layers of the Amundsen basin.