Combination of flow injection with capillary electrophoresis. Part 3. On-line sorption column preconcentration capillary electrophoresis system

A combined flow injection (FI)–capillary electrophoresis (CE) system with a split-flow interface reported previously was used for on-line preconcentration of pseudoephedrine by solid phase extraction on a micro-column packed with C18. Aqueous samples were loaded on the column at 1.0 ml min−1 for 90 s and eluted by a mixed eluent of 40% 62.5 mM acetate buffer (pH 4.0) and 60% acetonitrile at 0.2 ml min−1. A zone-sampling approach was employed to sample 45 μl of the most concentrated zone of the eluate, which was injected into the FI–CE split-flow interface using a phosphate buffer carrier, with a 25 μl water zone preceding the sampled eluate zone to achieve enhanced field amplification effects. Sensitivity enhancements of 60 fold (180 fold with 4 min sample loading) were thus achieved with a sample throughput of 9 h−1 and 4.7% relative standard deviations (n = 10, 2 μg ml−1 pseudoephedrine) for peak area evaluation, without significant degradation of column efficiency.