Channel Length & Flowrate
Increasing the length of a tubular channel decreases the peak height, while the peak shape changes from asymmetrical to symmetrical. At the same time, the resident time of the peak maximum increases with the distance traveled, and the peak base broadens.

This is the principal limitation of a system based on constant forward flow, since  the only way how to increase the incubation time is to increase the length of conduit ( cFI). Thus the incubation time  available for chemical reaction is about 20 seconds, when the  conduit length is 250 cm, and combined flow rates 3 mL/min. (The recording here was obtained at a flow rate of 1.4 mL/min as in slide 1.2.12.)

The use of programmable instead of continuous flow (pFI and SI) allows the incubation time to be prolonged by slowing or by stopping the flow, and speeds up the system wash by accelerating the flow. Programming the flow makes  both Flow Injection and Sequential Injection  more  efficient since it allows to minimize the volume of the flow channel and thus reagent consumption and waste generation.