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

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/μmol 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 three-fold, having interesting relationships with the peak potentials of single voltammetric curves.