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This clip demonstrates the merging of sample with reagent at a confluence point situated at the central port in two line SIA system. The sequence shows aspiration of 100 microliters of blue indicator dye from sample port into holding coil #1. Next, the valve is turned towards the reagent port (of 0.01 N HCl used as reagent ), and while 200 microliters solution is aspirated at a rate of 50 microliters/second into HC#2, 100 microliter the blue sample zone is pushed from HC#1 at the flow rate of 25 microliters/second, thus forming 1:1 sample/reagent mixture in holding coil#2. Next valve is turned towards the flow cell, flow is reversed and the yellow , acid form of the dye zone is passed through the flow cell. Finally the system is flushed with a burst of rapid flow.

Note that during sample and reagent aspiration in 1:1 confluence mode into the holding coil #2, the mixing is incomplete while the dye retreats into the holding coil. However, when the flow is reversed, the dye zone emerging from holding coil #2 is fully mixed and completely converted ito acid form.