On-column sample preconcentration in electrokinetic chromatography by sweeping with polymeric pseudo-stationary phases

This paper demonstrates in a practical manner the on-column preconcentration of hydrophobic solutes, such as quinine, alkyl phenones, and progesterone, by the sweeping mechanism using polymeric surfactants with highly acidic ionic head groups. The sulfonated and sulfated copolymers used showed high electrophoretic mobilities, high solubility, and good stability in organic/aqueous solutions with low pH values. More than 1000-fold increase in signal was observed for quinine, heptanophenone, and progesterone using sweeping in reversed-flow electrokinetic chromatography at low pH. The detection limit of quinine can be lower than 42 ppb (ng/mL) using a diode array UV detector. Quinine, a cationic hydrophobic solute with a relatively high retention factor, can be concentrated 5800 to 10,000-fold and separated from other hydrophobic solutes using a separation buffer containing a relatively high concentration of organic modifier. Under these conditions, detection of 12.5 ppb of quinine with a signal-to-noise ratio of 15 is achieved. The retention times and peak heights of hydrophobic solutes are shown to be reproducible.