The most powerful tools for optimizing SI based assay is the combination of stopping the flow, and controlling the temperature, while the desired chemical reactions are proceeding. The incubation can take place either in the holding coil(SHC) or in the flow cell (SFC), while either the holding coil or the flow cell is thermostated at an elevated temperature.
The readout in SHC mode resembles the flow injection response, since the reaction product flows interruptedly trough a flow cell. This is the, fast SI suitable for serial assays.
High sensitivity SI is performed in SFC mode, when the reaction product is arrested in the flow cell, yielding reaction rate curve.
These widely used nutrient assays, were chosen not only for their importance, but also because they represent a wide variety of chemistries, from very fast (nitrite) to very slow (silicate) reaction rates, and diverse reaction conditions and reagent composition.