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 (PO 4 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.

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or of alkyl phenyl phosphite, respectively. Methods applicable to phosphorus and nitrogen [Kolb et al. (94K) and ] and two methods applicable to phosphorus and sulfur [Patterson (136K) and Patterson and Howe (137K)] are described in the sulfur and nitrogen portions of this review.The determination of arsenic in catalytic reformer feedstocks by flameless atomic adsorption published by La Villa and Queraud (103K) involves adding 5 mL of 1% iodine in toluene, extracting twice with 10 mL of 1% nitric acid, evaporating the extract to dryness, adding 2 mL of 1% nitric acid, running the sample in the spectrometer, and comparing the results with those for a blank and for standard solutions of arsenic and magnesium. Michelot (114K) determined silicon in coking naphthas contaminated with siloxane antifoam agents by using a direct reading emission spectrometer equipped with a graphite rotating-disk electrode; the naphtha is diluted with mineral oil sufficient to reduce the combustion rate but not to affect the sensitivity.

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