Adaptation of a rFIA-GOF method for measuring Cu concentrations in estuarine waters

In this study, we adapted copper quantification to the CHEMINI instrumentation [1] using the colorimetric method based on reverse flow analysis (rFIA) with liquid core wavelength (GOF) detection, as recently described [2]. This method relies on the reduction of ferricyanide by L-glutathione in acidic media, with copper acting as the reaction catalyst. Various parameters (flow rates, reaction, injection loop and GOF length) were optimized using chemometric experimental designs. By adapting the method to seawater (salinity effect, metal and organic matter interferences), we achieved high-performance analytical limits in the subnanomolar range (detection limit = 0.03 nmol.L^-1, GOF 1 m). The first application of the method was conducted along the land-sea continuum from the Aulne estuary towards the Iroise Sea, measuring both soluble and dissolved copper concentrations (FeLINE project, [3]). The average copper concentrations obtained were comparable (5-20 nmol.L^-1) to those reported earlier in this system [4]. Concentrations decreased almost conservatively from the Aulne freshwaters (22.0 nM at S=0) towards the Bay of Brest (8.1 nM at S=34). and slightly increased toward the Iroise Sea (11.2 nM at S=35.2). The soluble copper fraction represented between 72% and 100% of the dissolved copper fraction, indicating a low contribution of high molecular weight colloidal Cu species (0.02-0.45 µm) in the Aulne estuary.

 

Figure : Evolution of dissolved copper DCu (<0.45µm) as a function of salinity along the Aulne estuary

 

[1]         R. Vuillemin et al., “CHEMINI: A new in situ CHEmical MINIaturized analyzer,” Deep. Res. Part I Oceanogr. Res. Pap., vol. 56, no. 8, pp. 1391–1399, 2009.

[2]         T. Wang et al., “A shipboard method for catalytic kinetic spectrophotometric determination of trace Cu(II) concentrations in seawater using reverse flow injection analysis coupled with a long path length liquid waveguide capillary cell,” Microchem. J., vol. 179, no. April, p. 107441, 2022.

[3]         A. Laes-Huon et al., “Rapid and simple determination of iron-porphyrin-like complexes ( Fe-Py ) in estuarine and marine waters,” vol. 244, no. May, 2022.

[4]         G. Bordin, “Distribution et évolution saisonnière du cuivre dissous dans un écosystème estuarien macrotidal d’Europe occidentale (estuaire de l’Aule, France),” Oceanol. Acta, vol. 14, no. 5, pp. 445–457, 1991.