Microchip electrophoresis has shown its potential of application in many fields

but its utilization in real world is still limited.To achieve a successful separation on a microchip through electrophoresis

many details have to be carefully taken into account

such as the liquid levels of each reservoir

the exact location of each electrode etc.

skillful operation is therefore required.In this paper

branched microchannels were introduced at the inlet end of the sampling channel and the outlet of the separation channel of traditional microchips for electrophoresis with a cross configuration.Additional reservoirs were made

and the liquid levels of these two reservoirs were lower than that of the sample reservoir and the buffer waste reservoir

maintaining continuous refreshing at the branched points through siphoning.With 2 fluorescein isothiocyanate labeled organophosphorus herbicides

ie.glyphosate and glufosinate

and a degradation product

(aminomethyl)phosphonic acid

the applicability of the proposed microchip was investigated.Results showed that with this kind of microchips

several improvements could be achieved.Firstly

the injection time for the consecutive analysis with pinched injection could be shortened due to its effectiveness to prevent the dilution of the sample in the sampling channel by the buffer during the separation periods.Secondly

the baseline drift due to the entrance of separation waste back to the detection point during the injection periods could be effectively eliminated.Thirdly

the repeatability of the consecutive analysis was therefore significantly improved

120 times of consecutive injection gave a relative standard deviation(RSD) of peak height as low as 056%(calculated for(aminomethyl)phosphonic acid) with replenishing of the buffer and sample every 40 injections.More importantly

by using the proposed microchip

a pre separation could be performed by controlling the injection time.Components migrating slower in the sample could be excluded from the injection into the separation channel

making it possible to get rid of most of sample matrix by tuning the separation condition to make analytes migrate faster than the matrix components.This kind of pre separation could simplify the electropherogram and avoid possible contamination of the separation microchannel

which is also beneficial to the reliability of microchip electrophoresis.