It turns out that the analytical performance of cFI-SE and pFI-SE methods is identical, although cFI-SE technique uses 4.5x2=9mL of reagents and 50 mL of sample per assay, while pFI-SE uses only 1.6mL of sample and 0.6mL of reagents, to perform a double loading cycle (sensitivity of 0.09 AU/ppB P or 2.8 AU/mM P at a rate of 12s/hr.). The cartridge used in cFI-SE method contains 3000 microliters of sorbent, while renewable microcolumn is fully packed with 20 microliters of sorbent.
This comparison should not be viewed as a critique of the pioneering works of Ma and coworkers, who tested the cFI-SE method on board performing sea water assays, while pFI-SE , presented here, is at its early stage of development. However, this comparison provides compelling input for further development of pFi-SE also, because the instrument used for pFI is more advanced, more robust and more reliable than cFI instruments, which have large internal volumes and are burdened by performance and running cost of peristaltic pumping. Furthermore, the pFI-LOV instrument can also be used to automate other nutrient assays (1.2.32.). (Ruzicka 2018, Hatta 2018)
As to the choice of methodology for determination of traces of nutrients in sea water, sorbent extraction is the method of choice, compared to long light path (LWG) flow cell or MAGIC method based on coprecipitation (Ma 2017 section 1)
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