Fast analysis of phenolic acids by electrokinetic supercharging-nonaqueous capillary electrophoresis

A method was developed to analyze phenolic acids by nonaqueous CE after online concentration with electrokinetic supercharging. The EOF was reversed using a polyelectrolyte multilayer approach based on the successive adsorption of poly(diallyldimethylamonium chloride) and poly(styrenesulfonate) to reduce the analysis time. The results showed that the coatings were stable during 40 consecutive injections. Four phenolic acids were separated within 8 min using 30 mM ammonium acetate (pH* 8.0). The electrokinetic injection time and terminator length of the electrokinetic supercharging method were optimized to improve the detection sensitivity. Under the optimized conditions (electrokinetic injection of 100 s, -10 kV; terminator of 20 mM 2-(cyclohexylamino) ethanesulfonic acid, 22 s, 0.5 psi), the sensitivity was enhanced from 300- to 440-fold. The detection limits, based on three times noise, were in the range 1.0-2.5 ng/mL.