Capillary electrochromatography using a fluoropolymer as the chromatographic support material

Fused-silica capillary columns were packed with ethylene chlorotrifluoroethylene (ECTFE) particles for use in capillary electrochromatography (CEC). Electroosmotic flow (EOF) was generated in these columns using acetonitrile-water mixtures as the mobile phase. Electroosmotic mobilities of 1.6 x 10^-4 cm² V^-1 s^-1 (linear velocities of 1 mm s^{- 1}) were observed using a mobile phase without an electrolyte present. The EOF in the ECTFE-packed columns is enhanced when using trifluoroacetic acid (TFA) as a mobile phase additive; electroosmotic mobilities of 3.65 x 10^-4 cm² V^-1 s^-1 (linear velocity of 2.5 mm s^-1) were observed. This enhancement of EOF is attributed to dynamic coating of the ECTFE particles by TFA. Other electrolytes (i.e., Tris/Tris-HCl buffer and H₃PO₄) in the mobile phase did not have such an enhancement of EOF. However, a slight enhancement of EOF is observed, for example, if small quantities of TFA are added to the mobile phase containing Tris buffer. The potential of ECTFE for CEC is demonstrated by separating a mixture of amino acids.