Sample preparation is an essential step in any bioanalytical procedure and very often the most challenging step in method development. Most of the currently used methods require a relatively large amount of sample and are time consuming. Here, we describe a new approach based on electromembrane extraction (EME) integrated in microfluidic polymer chips. This procedure is fast, requires only small amounts of sample, and may thus be used for monitoring drug metabolism and the formation of metabolites in real time.