Improvement of Reliability for Microchip Electrophoresis with Pinched Sample Injection Through Branched Microchannels
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KeyWord:microchip electrophoresis  pinched injection  microchannel  organophosphorus herbicide  repeatability
WEI Xuan,WANG Yan,WANG Zhao-yan,PU Qiao-sheng 1.College of Chemistry and Chemical Engineering,Lanzhou University;2.Tonghua Normal University;3.School of Pharmacy,Lanzhou niversity
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      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.