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A shape factor model for injection analysis of microchip sample electrophoresis

Abstract One key factor that plays a significant role in the efficiency of on-chip electrophoresis separation is the initial shape of the sample plug at injection. For microchips involved in separation, injection is a key step in efficient analysis, however, detailed analysis of the effect of sample plug shape and size at injection on separation efficiency is still lacking. In this article, we quantified sample plug shape at the intersection of injection and separation channels (cross) of a separation microchip by modifying the chip geometry and the injection procedure. To evaluate the injection plug, we introduce a shape factor model, correlated with separation resolution. Numerical simulations are conducted to control the plug shape through applied electric potentials, and the model is validated with experimental results in the literature. Analyzing the results of different injection configurations, we provide a two-step injection model to achieve the ideal rectangular shape and address the separation resolution for potential configurations at separation. Irrespective of the separation configurations, a good initial plug shape, assessed by the shape factor model, show well resolved sample constituents. At the onset of separation, results present higher resolution for higher applied potentials at the side reservoirs of the separation channel.