Design And Evaluation Of An Electroosmosis-driven Flow Gating Interface For The On-line Coupling Of Solid-phase Extraction With Capillary Electrophoresis

We present a new interface for the on-line coupling of solid-phase extraction(SPE)with capillary electrophoresis(CE).The construction and operation of the interface are introduced in detail.The interface is designed based on the principle of the flow gating,and the background buffer flow is driven by electroosmosis in the new interface instead of the pressure in the interfaces reported previously.The dead volume of the interface is approximately 15.7 nL.The operation conditions are investigated and selected using phenol as the test analyte.The ratio of peak height obtained through the electrokinetic injection via the interface to that obtained by direct electrokinetic injection is up to 99%,indicating that almost no dilution effect happens during injection in this interface.The reproducibility of injection via the interface was measured within 5 hours.The relative standard deviations of peak height,peak area and migration time are 4.1%,1.6% and 0.5%,respectively,indicating that the interface has good stability.An on-line coupling system of SPE-CE-UV was constructed using the new interface.The on-line coupling system was evaluated using a homemade MAA-co-EDMA monolithic column as the SPE column and using phenol and 4-nitrophenol as the test analytes under optimized extraction and interface operation conditions.The enrichment factors of phenol are 659 and 664 using the SPE-CE-UV system and SPE-UV part,respectively.The enrichment factors of 4-nitrophenol are 574 and 588 using the SPE-CE-UV system and SPE-UV part,respectively.This data shows that this interface does not degrade the enrichment factors of SPE.The SPE-CE-UV system was used to determine the content of phenol and 4-nitrophenol in river water.At three different spiked concentration levels,the recoveries of phenol range from 91.3% to 104.1%,the precisions are from 2.4% to 4.3%(RSD%,n=3),and the relative detection limit is 1.9 ?g/L.The recoveries of 4-nitrophenol are from93.8% to 103.5%,the precisions are from 2.7% to 3.1%(RSD%,n=3),and the detection limit is 2.1 ?g/L.These results show that the system has good accuracy,precision and detection ability.In addition,the SPE-CE-UV system has some good merits such as the low sample consumption,high automation,high sample throughput and easy operation.