An analysis of distinguishing composite dissolved metal–ligand systems measurable by stripping voltammetry

Abstract

International audienceVoltammetry is a method able to distinguish in certain degree the speciation of dissolved metals. An analysis of its ability to discern composite and more complex dissolved metal–ligand systems has been carried out by simulating the experiments for determination of metal–ligand complexing parameters. Logarithmic equidistant addition of metal was presumed, covering 2.5 decades. The data obtained with the preset parameter values were subsequently fitted to the presumed models. Data points under the detection limit DL = 10 −10 mol L −1 were eliminated and random noise following a realistic shape was added to the points to approach them to the real experiment. Four models were applied for simulation and up to five models for fitting. The analysis of the results shows that with the nowadays state-of-the-art measurement and data treatment techniques, in most of the cases it was possible to distinguish more complex and also more probable bi-ligand and mixed metal–ligand complexes from the simpler 1:1 metal–ligand systems. Statistical evidences to validate the right model were given. Its applicability has been confirmed by generating a similar data mining server (DMS) rule

Interpretation of complexometric titration data: An intercomparison of methods for estimating models of trace metal complexation by natural organic ligands

“…Significantly, this form of the speciation model variables almost exactly inverts the true independent ([M] T ) and dependent ([M f ]) variables of a titration, a trait shared by every linear and non-linear regression approach to varying extents (Table 1). Several studies have already discussed the problems these methods have with specific types of data (Apte et al, 1988;Garnier et al, 2004bGarnier et al, , 2005. For example, Gerringa et al (1995) showed that the VDBR linearization is more susceptible to outliers than the LG non-linear regression approach.…”

Characterisation and modelling of marine dissolved organic matter interactions with major and trace cations

“…However, due to experimental and fitting uncertainties, it has been shown in a theoretical study that the corresponding binding parameters are often inaccurately determined (Garnier et al, 2005). So, in this study DNOM binding properties towards cations were modelled using a discrete distribution of mono-dentate binding ligands (L Mi ), each defined by four parameters: a site density (L MiT in meq mol À1 C ) and stability constants (referring to the free cation concentrations) towards copper (K CuLi ), calcium (K CaLi ) and proton (pKa i ) (Garnier et al, 2004a;Sposito, 1981).…”

“…Obtained experimental potentiometric data were fitted using the software PROSECE (available on request, free of charge) which has already been successfully applied for potentiometric studies (Garnier et al, 2004c(Garnier et al, , 2005Lenoble et al, 2008). The fitting resulted in the determination of the optimal number of acidic sites with corresponding optimised protonation/stability constant (pKa) and density (L T ) values.…”

“…These sites are parameterized by fitting of the titration data using linear methods (Scatchard, 1949;Chau and Lum-Shue-Chan, 1974;Ružić , 1982) or more appropriate non-linear ones (Sposito, 1981;Kinniburgh et al, 1996;Tipping et al, 1998;Woolard and Linder, 1999;Town and Filella, 2002;Dudal and Gerard, 2004;Garnier et al, 2005). Due to low organic carbon content (0.1-1 mg C L À1 ; Vetter et al, 2007) associated with trace levels of metals (rarely higher than some nmol L À1 ), study of DNOM binding properties in unpolluted marine waters still remains a challenge.…”

Significance of data treatment and experimental setup on the determination of copper complexing parameters by anodic stripping voltammetry

“…For this purpose linearization method proposed by Ružić and vandenBerg is widely used [16,17], although non-linear fitting approaches were practiced and shown to be superior [3,7,18]. Distinguishing of more complex and also more probable bi-ligand and mixed metal-ligand complexes than simple 1:1 metal-ligand systems is shown to be achievable too [19]. One of the major factors obstructing the calculation of more complex metal-ligand system is the precision of measurements.…”