Electrophoresis　on　plastic　microchips　is　an　economic　way　for　rapid　separation　and　determination　of　multiple　analytes,　but　its　application　is　frequently　limited　by　the　unstable　electroosmotic　flow　(EOF)　and　non-specific　adsorption　of　certain　analytes　and　sample　matrices.　In　this　work,　cationic　polymer　poly　(diallyldimethylammonium　chloride)　(PDDA)　was　used　as　the　background　electrolyte　(BGE)　to　eliminate　the　non-specific　adsorption,　control　the　EOF,　regulate　the　viscosity　and　improve　the　separation　efficiency　on　cyclic　olefin　copolymer　microchips　with　75　mu　m　id　microchannels.　Three　rhodamine　dyes　that　are　easily　adsorbed　on　plastics　were　separated　in　the　presence　of　organic　solvents.　Influences　of　the　experimental　conditions　were　systematically　investigated　and　the　performance　was　compared　with　anionic　polymer　polyacrylic　acid　or　neutral　polymer　hydroxypropyl　cellulose.　The　effectiveness　of　ionic　polymers　for　the　modulation　of　EOF　was　demonstrated.　With　PDDA　as　BGE,　three　rhodamine　dyes　were　well　separated　and　baseline　separation　could　be　achieved　in　20　s　with　a　voltage　as　low　as　400　V　using　a　microchannel　of　1　cm　long　and　75　mu　m　id.　The　determination　of　rhodamine　dyes　in　foods　and　lipsticks　was　performed　to　verify　the　robustness　and　applicability　of　the　proposed　methods,　Separation　of　peptides　and　proteins　labeled　by　rhodamine　B　isothiocyanate　was　also　performed　with　the　proposed　running　medium.　(C)　2017　Elsevier　B.V.　All　rights　reserved.