The influence of sample matrix on sample sweeping in MEKC was examined in the presented manuscript. Significant focusing effect was observed for relatively hydrophobic cationic compounds (emetine, strychnine and quinine) using high ionic strength sample matrix (900mM H3PO4/720mMTris) which conductivity was about ninefold higher than utilized BGE. Moreover, the results were obtained using BGE composed of comparatively low surfactant concentration (10 mM SDS) and 40 mM H3PO4/32 mM Tris buffer solution. About 200 to 300-fold preconcentration of analytes was reached with the presented method. Basing on experimental results and computer simulation using Simul5 software, hypothetical mechanism of observed phenomenon was proposed.