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When first conceived, Sequential Injection had to be based on flow programming, since there is no other way how to meter and mix sample and reagent zones, when using only one valve and one pump. And the method did not really gain a wide acceptance in its original, macro, configuration. Only when the flow path was miniaturized in the lab-on-valve platform, the advantages of SI I became recognized, and the importance of pump design became evident.

What was available at the outset was a home made device (A), fabricated from a peristaltic pump – a cam driven syringe pump that generated a sinusoidal flow rate. (Ruzicka and Marshall 1990). While syringe pumps were available at that time, none of existing models could aspirate small discrete volumes at a controlled flow rate. Availability of Cavro pumps (B) facilitated the development of micro SI-LOV technique, which, however, is somewhat limited by the performance of this pump, as it has to be periodically refilled. The advantages of Miligat (C), synchronous refilling, along with a wide range of flow rates, are result of ingenious design, and of meticulous engineering. As shown in the previous pages, the combination of Miligat and LOV technologies leads to significant improvement of Si based assays.

Yet, presently available pumps still do have shortcomings. Cavro has to be periodically refilled, while Miligat is not well suited to pump strong acids or bases, is not transparent to the user, and has to be serviced professionally.

Hopefully, all possibilities for pump design are not yet exhausted, and there is a simple solution to construct of an “ideal” drive for flow based assays.

J. Ruzicka & G.D. Marshall, Anal. Chim. Acta, 237, 329, (1990).