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Various industries depend on knowing the exact concentrations of different iron species in their water. Traditional analytical methods often have difficulty to accurately distinguish between Fe(II) and Fe(III) because they have similar chemical properties. This leads to errors and incorrect data, hindering advancements in critical fields like energy generation/storage and research into chemical or electrochemical processes.

Cathodic sweeping voltammetry (CSV) overcomes these challenges and offers a robust, cost-effective, and convenient alternative to other techniques. Its ability to distinguish between ferrous and ferric iron is unparalleled. This improved accuracy enables scientists to make significant steps in technological research and industrial efficiency. In this Application Note, the Multi-Mode Electrode pro is used to simultaneously determine Fe(II) and Fe(III) in water.

Check standard solutions

884 Professional VA manual for MME.
Figure 1. 884 Professional VA manual for MME.

Add the water sample to a vessel filled with degassed electrolyte. Use two standard additions with separate Fe(II) and Fe(III) standard solutions to perform the quantification.

Table 1. Parameters
Parameter Setting
Mode DME
Start potential 0.0 V
End potential -1.5 V
Sweep rate 30 mV/s
Peak potential Fe(II) -0.25 V
Peak potential Fe(III) -0.8 V
  • Multi-Mode Electrode pro
Results of iron speciation determination in a check  standard solution by CSV.
Figure 2. Results of iron speciation determination in a check standard solution by CSV.

The voltammogram shown in Figure 2 illustrates the successful determination of Fe(II) and Fe(III) species in a solution containing 0.5 mg/L of each. The clear resolution of the two peaks demonstrates the capability of the method to differentiate and quantify Fe(II) and Fe(III) in a mixed solution.

Table 2. Result
Sample Fe(II) (mg/L) Fe(III) (mg/L)
Check standard solution 0.507 0.516

Metrohm AG

9100 Herisau


Internal references: AW VA CH4-0543-112015