The paper describes a comprehensive study of the importance of cations to improve the efficiency and mass transfer in the electromembrane extraction for the determination of non-steroidal antiinflammatory. The procedure has been demonstrated to be adequate for the analysis of the selected non-steroidal anti-inflammatory drugs in human urine samples. Effects of donor and acceptor solution composition were examined studying the presence of different counter-ions in both aqueous solutions demonstrating to be an important parameter in the transference of the analytes across the membrane. Other parameters that are also critical for electromembrane, such as the organic solvent, the voltage, the extraction time and the donor solution volume were also optimized. The extracts were analyzed by high performance liquid chromatography with diode array and fluorescence detection. The highest enrichment factor was achieved using a pH 7 donor composition adjusted with KOH and an acceptor composition at pH 12 adjusted with NaOH. The enrichment factors were within the range of 85 and 133 for all compounds after 20 min extraction, using a voltage of 60 V, a stirring speed of 600 rpm and 1-octanol as support liquid membrane. Detection and quantitation limits were within 0.1-1.5 ng mL(-1) and 0.3-3.0 ng mL(-1), respectively. The presence of K+ and Na+ as counter ions in the donor and the acceptor solution, respectively, demonstrated a higher enrichment compared to previous reported methods for the determination of non-steroidal antiinflammatory by electromembrane extraction using NaOH/NaOH as counter-ions.