A Sheath Flow Gating Interface For The On-line Coupling Of Solid-phase Extraction With Capillary Electrophoresis

An interface, named sheath flow gating interface (SFGI), is presented for the on–linecoupling of solid-phase extraction (SPE) with capillary electrophoresis (CE). The design,construction and operation of the SFGI are described in detail. The SFGI originally adopts asheath flow design based on the flow gating principle. This design allows the void volume ofthe SFGI to be minimized to nanolitres. The SFGI allows for direct observation and routinemanipulation of the SPE and CE capillaries, and works well over a wide range of SPE eluentflow rates with the operation conditioned simply. The SFGI is evaluated in terms of dilutioneffect, peak symmetry, column efficiency, reproducibility and long-term stability with asimplified SPE–CE–UV system using two organic acids as the test analytes. The injectionefficiency, defined as the ratio of the peak height obtained using the SFGI to that by directelectrokinetic injection, is up to98%, indicating that almost no dilution effect occurs duringinjections in the SFGI. The data on peak symmetry and plate numbers obtained using theSFGI are comparable to those obtained by direct injection, demonstrating that the SFGIhardly introduces extra-column effects into CE separations. The precisions (RSD%) obtainedthrough100repeat injections over a3.5h period are2.4%,5.4%and3.1%for peak height,peak area and migration time, respectively. Other features of the SFGI include simplicity ofconstruction and ease of operation. The above merits of the SFGI suggest a great potential forroutine use of the SFGI in coupling SPE with CE.