Author: Alfonso Lcdo. en Químicas Berduque

Publisher:

Published: 2006

Total Pages: 238

ISBN-13:

This thesis presents investigations into the use of electrochemistry at liquidliquid interfaces in different areas of analytical chemistry: extraction chemistry and detection chemistry. The electrochemistry of different generations of poly(propylenimine), (DAB-AM-n) and poly(amidoamine) (PAMAM) dendrimers was studied, with no need for dendrimer labelling with electroactive functionalities to enable the detection. The detection was based on the transfer across the Interface between Two Immiscible Electrolyte Solutions (ITIES) of low concentrations of dendrimers presenting a net charge in solution. The electrochemical behaviour of the dendrimers was observed to be quite different depending on the dendrimer family, the generation number and the experimental pH. The electrochemical detection of the lower dendrimer generations presented similar behaviour to that observed for traditional ion transfer of simple ionic species. However, the increase of the generation number resulted in very distorted voltammograms. The formal transfer polential, Gibbs free energies of transfer and the net charge of the dendrimers were determined using cyclic voltammetry. Electrochemistry at the ITIES is presented as a method of electrochemically modulated liquidliquid extraction of ions, where ions in a mixture can be selectively partitioned as a function of the applied interfacial potential difference. A hydrodynamic flow-injection system was designed for the potentiostatic extraction of non-redox-active species from a flowing aqueous phase into a stationary organogel phase. The ions tetraethylammonium (TEA+), 4-octylbenzenesulfonate (4-OBSA-), and p-toluenesulfonate (p-TSA-) were studies as model analytes. The extraction study comprised examination of the influence of extraction potentials, aqueous phase flow rate and target species concentration. The extraction process can be monitored in situ by means of the ion transfer current, which has opposing signs for anions and cations. Hydrodynamic voltammograms were obtained from these experiments. The selective extraction of 4-OBSA- from its mixture with p-TSA-, as well as co-extraction of both anions is demonstrated. Mixtures comprising 4-OBSA- and TEA+ ions were also evaluated. The application of negative potential differences enabled the selective extraction of 4-OBSA- into the organic phase, and more positive potential differences enabled the selective extraction of TEA+. However, intermediate potentials lead to the co-extraction of both ions into the organic phase, with apparent selectivity for TEA+ over 4-OBSA-. An increased concentration of either ion in the mixture inhibited the extraction response of the other ion, but the order of the extraction at these intermediate potentials was always TEA+ followed by 4-OBSA-. The reasons for the selectivity for the cation over the anion are discussed.