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.

Assay Protocols, Fast and High Sensitivity SI
With aim to demonstrate the efficiency and versatility of SHC and SFC techniques, as compared to other flow based methods, the following reagent based assays have been automated:

  • Nitrite by Gries Reaction (2.2.17.)
  • Nitrate by Cd reduction (2.2.19.)
  • Phosphate  by Molybdenum Blue (2.2.24.)
  • Silicate by Molybdenum Blue (2.2.31.)
  • Ammonia by Salicylate method (2.2.34.)

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.