Investigation of  Phosphomolybdenum Blue Method
By Programmable Flow Injection

There are two objectives of this study. The first one is to show how Flow Injection, programmed to function in a batch mode, can be used to investigate reagent based assay by monitoring reaction rates and spectra of ongoing chemical reactions.

The second aim is to optimize the phosphate assay based on formation of phosphomolybdenum blue (PMoB) – a widely used, yet still  rather unexplored method, the complexity of which was recently compared to “black box” (Nagul 2015)

Determination of phosphate by the molybdenum blue method (PMoB) is based on two step reaction. The first one is formation of a polymolybdate structure around the phosphate anion, while during the second step, the yellow phosphomolybdate is reduced to phosphomolybdenum blue:

Reduction by  ascorbic acid in the presence of Sb (Murphy, Riley 1962), is most frequently used, because  it enhances the rate of formation of PMoB, thus making  the method suitable for automation by Flow Injection. Absorbance  of thus formed PMoB measured at  880nm, yields detection limit well below  micro molar phosphate concentrations, thus making the PMoB method widely used in oceanography and environmental studies.

This section is organized along the following topics:

1.5.7.    PMoB method – what we know and what we do not know.
1.5.8.    Instrumentation and reagents.
1.5.9.    Flow programming and data collection.
1.5.10.  [H+] diagrams: acidity and molybdate concentrations
1.5.13.  Molar absorptivity of PMoB and  [H+] diagrams.
1.5.14.  How to optimize the PMoB assay.
1.5.15.  SUMMARY

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