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Separation is a critical process for both posttreatment of synthesis and sample pretreatment of instrumental analysis.While shrinking separation columns to micro-or nano-scale,separation speeds and efficiencies can be increased significantly along with less sample and buffer consumption.However,throughput mismatch with regular size sample preparation and/or downstream analysis procedures limits further application of microfluidic separation technique.Continuous-flow microfluidics offers a possible solution for the throughput mismatch issue.For example,micro free flow electrophoresis(μFFE)is a valuable technique capable of high throughput rapid microscale electrophoretic separation along with mild operating conditions.Unfortunately,the stream flow separation nature of free flow electrophoresis affects its separation performance with additional stream broadening due to sample stream deflection.To reduce stream broadening and enhance separation performance of μFFE,we presented a simple microfluidic device that enables injection bandwidth control [1].In this talk,we report the formation of pinched injections in a μFFE system using operating buffer and sample flow rate ratio(r)setting.Initial bandwidth at the entrance of separation chamber can be shrunk from 800 to 30 μm when r increased from 1 to 256 as showing in Figure 1 A and B.Stream broadening at the exit of separation chamber can be reduced by about 96%when r increased from 4 to 128,according to both theoretical and experimental results.Moreover,the separation resolution for a dye mixture,showing in Figure 1 C and D,was enhanced by a factor of 4 when r increased from 16 to 128,which corresponded to an 80%reduction in sample initial bandwidth.This enhancement can be further amplified by combination with other resolution improving approaches and will extend the application of μFFE technique.For example,isolating electrodes from the separation chamber can improve the stability of μFFE separation and adopting multichannel at the end of separation chamber may increase efficiency of separation components collection in the reported device.Additionally,the reported chip device is easily fabricated and operated,as well as readily integrated into regular size sample preparation and/or downstream analysis procedures.