Capillary electrochromatography using a strong cation-exchange column witha dynamically modified cationic surfactant

A novel mode of capillary electrochromatography (CEC), called dynamically m odified strong cation-exchange CEC (DMSCX-CEC), is described in this paper. A column packed with a strong cation-exchange (SCX) packing material was d ynamically modified with a long-chain quaternary ammonium salt, cetyltrimet hylammonium bromide (CTAB), which was added to the mobile phase. CTAB ions were adsorbed onto the surface of the SCX packing material, and the resulti ng hydrophobic layer on this packing was used as the stationary phase. Usin g the dynamically modified SCX column, neutral solutes were separated with the CEC mode. The highest number of theoretical plates obtained was about 1 90 000/m, and the relative standard deviations (RSD's) for migration times and capacity factors of alkylbenzenes were less than 1.0% and 2.0% for five consecutive runs, respectively. The effects of CTAB and methanol concentra tions and the pH value of the mobile phase on the electroosmotic flow and t he separation mechanism were investigated. Excellent simultaneous separatio n of the basic and neutral solutes in DMSCX-CEC with a high-pH mobile phase was obtained, A mixture containing the acidic, basic, and neutral compound s was well separated in this mode with a low-pH mobile phase; however, peak tailing for basic compounds was observed in this mobile phase.