Development of a tubular sensor based on a polypyrrole-doped membrane for the potentiometric determination of the dodecylsulfate anion in a FIA system

Potentiostatic polymerization of polypyrrole doped with dodecylsulfate anion (DS-) was carried out in situ over a tubular composite (graphite-epoxy resin) support in order to develop a potentiometric DS- sensor (TISE) suitable for flow injection analysis (FIA). The sensibility of the TISE was maximized using the SIMPLEX algorithm in terms of the concentration of the pyrrole monomer, the concentration of DS-, the potential imposed and polymerization time. Response times between 2 and 4 minutes were observed. The analytical parameters obtained with the flow system were compared with those obtained in batch studies. In both, flow and batch analysis, potential vs. DS- concentration curves displayed two linear regions with different slopes. Flow analysis for DS- ion brings a total linear range of 1.58 x 10(-5) M to 3.88 x 10(-3) M with a maximum sensibility of 36.4 mV/concentration decade, meanwhile in batch studies the total linear range found was of 6.31 x 10(-6) M to 1.0 x 10(-3) M with a maximum sensibility of 54.49 mV The flow system response pH range was from 5 to 8. The reproducibility in terms of the relative error of the mean of different experiments was 1.58%. Two salient features of the system designed and built are worthy of mention: the sensor presented high selectivity to the dodecyl sulfate ion as compared to other inorganic anions including other anionic surfactants. The sensor lifetime in the FIA system by means of the sensibility changes was found to be of approximately four months.