Electrochemically controlled solid-phase microextraction and preconcentration using polypyrrole coated microarray electrodes in a flow system

Polypyrrole coated microarray electrodes have been used for electrochemically controlled solid-phase microextraction and preconcentration on individually addressable gold microband electrodes. In this study, a flow of analyte solution was maintained over the band electrodes by positioning a capillary in a vertical position over the electrode array during both the extraction and the detection of the desorbed compounds. This experimental set-up was used to evaluate the possibilities of using electrochemically controlled solid-phase microextraction with conducting polymers as a preconcentration step in miniaturised flow systems. The performance of the polymer, which was prepared by electrochemical polymerisation using a solution of 0.05 M pyrrole and 0.1 M LiClO4, was investigated using chloride as a model analyte employing different extraction times and analyte concentrations. It was found that significant preconcentration was possible using extraction times of only a few minutes and that a good linearity between the extraction time and detection response was present both for mM and microM chloride concentrations. Compared to a recent study (Liljegren et al., Analyst, 2002, 127, 591-597), using a more traditional solid-phase microextraction technique under electrochemical control, the preconcentration factor could be increased by a factor of about 210 by using the present flow system based approach. This increase in the preconcentration factor can be explained by the significant decrease in the desorption volume (i.e. reduced dilution of the desorbed analyte) associated with the use of the present flow system. With the present approach, the detection limit for the model analyte chloride could be decreased from 10 microM to 625 nM employing an extraction time of 180 s.