title: Reagentless and calibrationless silicate measurement in oceanic waters.
abstract: Determination of silicate concentration in seawater without addition of liquid reagents was the key prerequisite for developing an autonomous in situ electrochemical silicate sensor (Lacombe et al., 2007) [11]. The present challenge is to address the issue of calibrationless determination. To achieve such an objective, we chose chronoamperometry performed successively on planar microelectrode (ME) and ultramicroelectrode (UME) among the various possibilities. This analytical method allows estimating simultaneously the diffusion coefficient and the concentration of the studied species. Results obtained with ferrocyanide are in excellent agreement with values of the imposed concentration and diffusion coefficient found in the literature. For the silicate reagentless method, successive chronoamperometric measurements have been performed using a pair of gold disk electrodes for both UME and ME. Our calibrationless method was tested with different concentrations of silicate in artificial seawater from 55 to 140×10(-6) mol L(-1). The average value obtained for the diffusion coefficient of the silicomolybdic complex is 2.2±0.4×10(-6) cm(2) s(-1), consistent with diffusion coefficient values of molecules in liquid media. Good results were observed when comparing known concentration of silicate with experimentally derived ones. Further work is underway to explore silicate determination within the lower range of oceanic silicate concentration, down to 0.1×10(-6) mol L(-1).
authors: Laboratoire d'Etudes en Géophysique et Océanographie Spatiales, Centre National de la Recherche Scientifique, UMR CNRS 5566, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France.
authors: William
authors: W
authors: Giraud
authors: Ludovic
authors: L
authors: Lesven
authors: Justyna
authors: J
authors: Jońca
authors: Carole
authors: C
authors: Barus
authors: Margaux
authors: M
authors: Gourdal
authors: Danièle
authors: D
authors: Thouron
authors: Véronique
authors: V
authors: Garçon
authors: Maurice
authors: M
authors: Comtat