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Lookup NU author(s): Dr Philippa RickardORCiD, Dr Guenther Uher, Professor Robert Upstill-GoddardORCiD
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).
Surfactants, or surface-active substances (SAS), are amphipathic organic substances thatadsorb on aquatic phase boundaries, including the air-sea interface that covers ~70% ofEarth’s surface. SAS thus mediate all mass transfer across the air-sea interface and arecentral to planetary scale biogeochemical processes. SAS are routinely quantified inseawater and freshwater in terms of total surfactant activity (SA), using alternating current(AC) out-of-phase voltammetry with a hanging mercury drop electrode (HMDE). Althoughthis technique is well established, method modifications have been implemented anddiffering calibration procedures adopted in individual research laboratories. Increasinginterest in the environmental roles of SAS prompts a timely inter-comparison of thesevarying analytical approaches. Using sea-surface microlayer (SML: uppermost 80 μm layersampled) and sub-surface (SSW: 1 m depth sampled) seawater from Jade Bay (southeasternNorth Sea), we carried out the first inter-laboratory comparison for SA, usingmethods and calibration protocols previously established in three participating laboratories.Internal calibration protocol follows direct calibrations of individual samples against themodel surfactant Triton-X-100 during analysis, whereas external calibration producesindependent Triton-X-100 calibration curves; both protocols express SAS concentrations inTriton-X-100 equivalents (T-X-100 eq.). There was no significant difference between SAderived via internal or external calibration protocols, or by using different analyticalinstruments (range in Kruskall-Wallis and Dunn-Bonferroni post-hoc test p-values: 0.062-1.000), except where freeze/thaw degradation was suspected to have occurred during transit(p < 0.001). We recommend using discrete calibration standards during external calibration.Irrespective of any differences in SA determined by the three laboratories, the SAenrichment factor (EF: = SASML/SASSW) was not affected for any sample; the root meansquare error (± one standard deviation) between all laboratories was 0.156 ± 0. 226 (n = 45).We present and discuss recommendations for a standard analytical protocol to ensure theinter-laboratory compatibility of SAS measurements into the future.
Author(s): Rickard PC, Uher G, Upstill-Goddard RC, Frka S, Mustaffa NIH, Banko-Kubis HM, Kusan AC, Gasparovic B, Stolle C, Wurl O, Ribas-Ribas M
Publication type: Article
Publication status: Published
Journal: Marine Chemistry
Year: 2019
Volume: 208
Pages: 103-111
Print publication date: 20/01/2019
Online publication date: 03/12/2018
Acceptance date: 30/11/2018
Date deposited: 04/12/2018
ISSN (electronic): 0304-4203
Publisher: Elsevier
URL: https://doi.org/10.1016/j.marchem.2018.11.012
DOI: 10.1016/j.marchem.2018.11.012
Notes: Co-authored with RC Upstill-Goddard, School of Natural and Environmental Sciences
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