Pseudopolarography of lead (II) in sediment and in interstitial water measured with a solid microelectrode

Abstract

Pseudopolarograms of lead (II) constructed from the voltammograms measured in situ in the sediment and in the interstitial water by using an Ir solid microelectrode with a thin mercury film have shown as a kind of fingerprints of the sample. Despite shortcomings when compared to measurements with the mercury drop electrode and in model solutions, the measurement procedure was adapted for enough signal repeatability, avoiding to a reasonable extent the memory effect and electrode surface blocking. To make the best use of the information available, besides the classical pseudopolarograms, i.e. besides the dependence of the peak-height on the deposition potential, it is necessary to analyze the peak-area, the peak-position and the half-peak width versus deposition potential, and combine them with the knowledge from various theoretical and model situations. They have shown to contain interesting information about speciation. This information is not always unambiguous, it is often semi-quantitative, and cannot be reached by other methods, however, in combination with other methods it could be useful for the characterization of the sample solution. Pseudopolarograms of lead (II) in different liquid fractions of the sediment were measured and compared, the electrode sensitivity varying from 4 to 20 nA/mol L −1 of lead (II). The differences in half-wave potentials recorded were ranging up to 0.6 V and those in the slopes of pseudopolarograms were threefold , having interesting relationships with the peak potentials of single voltammetric curves.

Speciation of trace metals in natural waters: The influence of an adsorbed layer of natural organic matter (NOM) on voltammetric behaviour of copper

“…The height of the first wave at −0.2 V barely reaches 50% of the equivalent wave using the desorption step (curve 2), while the wave at the more negative potential (around −1.3 V) expands from −0.9 to −1.5 V. An additional (third) poorly resolved wave appears at a potential around −0.5 V. Compared to curve 2, a considerable detachment is evident by applying the desorption step. As pointed out in several papers, the position, numbers, and shape of the pseudopolarographic waves is dependent on the metal complexes existing in the sample [10,[12][13][14][15][16][17][18][19][20][21][22][23]37], and stability constants of labile metal complexes can easily be calculated [12][13][14][15]38]. The more negative pseudopolarographic wave that we obtained using the desorption step corresponds to a thermodynamic stability constant of the formed complex in the order of log K ∼39 (estimated according to "chelate scale" previously presented by group of Luther III [12][13][14][15]).…”

Voltammetric procedure for trace metal analysis in polluted natural waters using homemade bare gold-disk microelectrodes

“…Total dissolved metal concentrations in the water sampled on 16 . Considering these values, analysis carried out in the River Deûle samples has focussed on the measurements of Cu, Pb and Zn.…”

“…In this case, a monitoring system is introduced in the water column, though the voltammetric measurements are not really performed in situ because of the necessity for removing oxygen from the sample before analysis. Another attempt with Ir microelectrodes with only traces of mercury was successful for Pb and Cd determination and measurements in box-core sediments [16]. Preparation for in-field measurements has been carried out on gold electrodes in acidic solutions [17,18], solid dental amalgam electrodes [19,20] and alloys [21].…”

Critical review perspective: elemental speciation analysis methods in environmental chemistry - moving towards methodological integration

“…For instance, strong Cd 2+ complexes with log K ML ranging between 21.5 and 32 were detected at different sites in a river and at different times of the year. [46] Similar K ML values were found at the different sites, which suggests that similar ligands, but strong differences were observed between June and September. Recent studies investigated the complexation of Cu and Zn by concentrated marine dissolved natural organic matter (NOM).…”

“…PP has been mainly used in sea water, [44] in freshwater [45] and also directly in situ in an interstitial sediment water. [46] Although the ligand concentration cannot be obtained, the presence and the strength of these complexes are valuable information. For instance, strong Cd 2+ complexes with log K ML ranging between 21.5 and 32 were detected at different sites in a river and at different times of the year.…”