Ionic liquids as modifiers for glass and SU-8 electrochemical microfluidic chips

Ionic liquids have been attracting attention as background additives to improve separations in the last years. This work reports about the use of four ionic liquids (ILs): 1-butyl-4-methylpyridinum tetrafluoroborate (BMPyBF4), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), 1-butyl-3-methylimidazolium hydrogen sulfate (BMIMHSO4) and 1-ethyl-3-methylimidazolium methyl sulfate (EMIMMeSO4) as dynamic modifiers in glass and SU-8 microchip electrophoresis (ME). The influence of varying pH values and ILs concentration on the detection system was investigated. Moreover, ionic liquids with different cations and counterions were evaluated as background additives choosing two catecholamines (dopamine, DA and epinephrine, E) as model analytes. Dynamic modification with ILs proved to be necessary to obtain enhanced mixture separation in both 30 mm glass and SU-8 MEs. Good precision in terms of migration times and resolution was obtained for both kinds of MEs when ILs were employed. In addition, baseline resolution with good reproducibility over time (RSD values of 0.5% and 0.8% for migration times in one experiment and three days, respectively) was achieved in glass MEs with 60 mm effective separation length.