Analytica Chimica Acta 569 (2006) 244–249 Application of a simple voltammetric method to the determination of refractory organic substances in freshwaters Vincent Chanudet a,b , Montserrat Filella b , Franc ¸ois Quentel c,∗ a Institut F.A. Forel, University of Geneva, Route de Suisse 10, CH-1290 Versoix, Switzerland b Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, Quai Ernest-Ansermet 30, CH-1211 Geneva 4, Switzerland c Laboratoire de Chimie Analytique, UMR-CNRS 6521, Universit´ e de Bretagne Occidentale, 6 avenue V. Le Gorgeu, CS 93837; F-29238 Brest Cedex 3, France Received 7 December 2005; received in revised form 28 March 2006; accepted 29 March 2006 Available online 4 April 2006 Abstract A method based on the peak obtained by adsorptive stripping voltammetry for the complex formed by organic matter in the presence of trace amounts of molybdenum(VI) has been tested for the determination of refractory organic matter, the so-called humic substances, in freshwaters. The method is rapid and particularly well-adapted to the determination of low amounts of refractory organic matter. It has a detection limit of 2.4 gCL -1 for 3 min deposition time. The effect of the presence of other types of natural organic matter has been tested. The method has been applied to a wide variety of freshwaters at different trophic states. © 2006 Elsevier B.V. All rights reserved. Keywords: AdSV; Fulvic acids; Freshwaters; Humic acids; Molybdenum(VI); Refractory organic matter 1. Introduction Different types of natural organic matter (NOM), produced in various environmental compartments, are present in surface freshwaters. NOM can be leached from soils or peat bogs, dif- fused from sediments, and released by plankton and bacteria. The NOM in any ecosystem can be roughly divided into two parts, the larger of which is quickly reused for the growth of organisms while a smaller part, which is not easily degraded, is accumulated in aquatic systems (refractory organic matter, ROM). Thus, a significant proportion of the NOM present in unpolluted surface freshwaters is composed of fairly stable compounds produced either in the soil (pedogenic) or in the water body (aquagenic). The pedogenic refractory organic mat- ter (PROM) is basically made up of fulvic acid (FA) molecules. Other pedogenic refractory macromolecules, such as humic acids (HA), are mostly retained by soil particles. The aqua- genic refractory organic matter (AROM) is mainly produced by the macrophytes and by plankton decomposition. The other compounds present in freshwaters are individual pedogenic and ∗ Corresponding author. E-mail address: Francois.Quentel@univ-brest.fr (F. Quentel). aquagenic proteinaceous compounds and polysaccharides. The majority belong to the pool of quickly degraded NOM, but some proteins and polysaccharides remain for significant amounts of time in aquatic systems. At present, there is no method for identifying and quantifying all types of NOM. Studies have focused mainly on the refrac- tory fraction of NOM, both in soils and in freshwaters, mainly because of the key role that it plays in trace metal fate. It is common practice to isolate the hydrophobic fraction of ROM in freshwaters by adsorption onto non-ionic resins and elution with alkali [1–4]. After isolation, characterisation is carried out by a variety of methods [5–13]. However, quantitative determination of ROM is rare. For instance, direct quantitative applications of the resin-based isolation method do exist [14,15] but the pro- cedure is time-consuming and there are very few examples of it. Various spectroscopic and chromatographic techniques have been used mainly to study ROM properties [16–31] but again their use as quantification tools is not widespread [32]. There is a clear demand for a rapid, reliable, non-time and non-sample consuming method for ROM determination. This study looks at the application of a fast, non-perturbing method to the determination of the refractory fraction of NOM, often known as the fulvic and/or humic fraction, in freshwaters. Although, strictly speaking, these terms should refer only to 0003-2670/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2006.03.097