Key factors in electromembrane microextraction systems for metals analysis in natural waters

Application of an electric potential to hollow fibre liquid phase microextraction (HF-LPME) systems previously optimised for metals preconcentration from natural waters could improve their analytical performance increasing enrichment factors and reducing operation times. Nevertheless, the effectiveness of the direct application of an electric potential to these systems may be limited due to the effects produced by other operational parameters. In this work, the effect of a variable electric potential on the enrichment factors of four HF-LPME systems used for the analysis of trace metals in natural waters (Cd, Ni, Ag and Cu) has been studied. In addition, the effect of organic phase composition, distance between electrodes and electrodes diameter has been also studied. From the results obtained, composition of organic phase can be considered as the key factor in electromembrane (EME) systems, since its polarity determine the operational range of the applied electric potential and consequently the enrichment factor that could be achieved. EMEs have demonstrated to be a real alternative to preconcentrate Cd, Ag and Cu from natural water samples in very short times (30 min). In fact, enrichment factors increased up to one order of magnitude if compared with HF-LPME methodology without application of an electrical potential.