We report the dynamical migration behavior of rigid polystyrene microparticles at an interface of coflowing streams of primary CP1 (aqueous) and secondary CP2 (oils) immiscible phases at low Reynolds numbers (Re) in a microchannel. The microparticles initially suspended in the CP1 either continue to flow in the bulk CPI or migrate across the interface into CP2, when the stream width of the CP1 approaches the diameter of the microparticles. Experiments were performed with different secondary phases and it is found that the migration criterion depends on the sign of the spreading parameter S and the presence of surfactant at the interface. To substantiate the migration criterion, experiments were also carried out by suspending the microparticles in CP2 (oil phase). Our study reveals that in case of aqueous silicone oil combination, the microparticles get attached to the interface since S < 0 and the three phase contact angle, 0 > 90 degrees. For complete detachment of microparticles from the interface into the secondary phase, additional energy AG is needed. We discuss the role of interfacial perturbation, which causes detachment of microparticles from the interface. In case of mineral and olive oils, the surfactants present at the interface prevents attachment of the microparticles to the interface due to the repulsive disjoining pressure. Finally, using a aqueous-silicone oil system, we demonstrate size based sorting of microparticles of size 25 gm and 15 gm respectively from that of 15 gm and 10 gm and study the variation of separation efficiency eta with the ratio of the width of the aqueous stream to the diameter of the microparticles rho. (C) 2017 Elsevier Inc. All rights reserved.