Realistic measurement uncertainties for marine macronutrient measurements conducted using gas segmented flow and Lab-on-Chip techniques

A J Birchill; G Clinton-Bailey; R Hanz; E Mawji; T Cariou; C White; S J Ussher; P J Worsfold; E P Achterberg; M Mowlem

doi:10.1016/j.talanta.2019.03.032

Realistic measurement uncertainties for marine macronutrient measurements conducted using gas segmented flow and Lab-on-Chip techniques

Talanta. 2019 Aug 1:200:228-235. doi: 10.1016/j.talanta.2019.03.032. Epub 2019 Mar 8.

Authors

A J Birchill¹, G Clinton-Bailey², R Hanz², E Mawji³, T Cariou⁴, C White⁵, S J Ussher⁵, P J Worsfold⁵, E P Achterberg⁶, M Mowlem²

Affiliations

¹ Ocean Technology and Engineering, National Oceanography Centre, European Way, Southampton SO14 3ZH, United Kingdom. Electronic address: anchill@noc.ac.uk.
² Ocean Technology and Engineering, National Oceanography Centre, European Way, Southampton SO14 3ZH, United Kingdom.
³ Ocean Biogeochemistry and Ecosystems, National Oceanography Centre, European Way, Southampton SO14 3ZH, United Kingdom.
⁴ Sorbonne Universités, UPMC Univ Paris 06, CNRS, Fédération de Recherche (FR2424), Station Biologique de Roscoff, 29680 Roscoff, France.
⁵ School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, United Kingdom.
⁶ GEOMAR Helmholtz Centre for Ocean Research, 24148 Kiel, Germany.

PMID: 31036178
DOI: 10.1016/j.talanta.2019.03.032

Abstract

Accurate and precise measurements of marine macronutrient concentrations are fundamental to our understanding of biogeochemical cycles in the ocean. Quantifying the measurement uncertainty associated with macronutrient measurements remains a challenge. Large systematic biases (up to 10%) have been identified between datasets, restricting the ability of marine biogeochemists to distinguish between the effects of environmental processes and analytical uncertainty. In this study we combine the routine analyses of certified reference materials (CRMs) with the application of a simple statistical technique to quantify the combined (random + systematic) measurement uncertainty associated with marine macronutrient measurements using gas segmented flow techniques. We demonstrate that it is realistic to achieve combined uncertainties of ~1-4% for nitrate + nitrite (ΣNOx), phosphate (PO₄^3-) and silicic acid (Si(OH)₄) measurements. This approach requires only the routine analyses of CRMs (i.e. it does not require inter-comparison exercises). As CRMs for marine macronutrients are now commercially available, it is advocated that this simple approach can improve the comparability of marine macronutrient datasets and therefore should be adopted as 'best practice'. Novel autonomous Lab-on-Chip (LoC) technology is currently maturing to a point where it will soon become part of the marine chemist's standard analytical toolkit used to determine marine macronutrient concentrations. Therefore, it is critical that a complete understanding of the measurement uncertainty of data produced by LoC analysers is achieved. In this study we analysed CRMs using 7 different LoC ΣNOx analysers to estimate a combined measurement uncertainty of < 5%. This demonstrates that with high quality manufacturing and laboratory practices, LoC analysers routinely produce high quality measurements of marine macronutrient concentrations.

Keywords: Intercomparison; Lab-on-Chip; Macronutrient; Measurement uncertainty; Nitrate; Phosphate; Segmented flow.