Ionic polymer enhanced electrophoresis in plastic microchips for rapid and robust determination of rhodamine dyes

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   μm 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   μm 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.