Determination of Iron and Its Redox Speciation in Seawater Using Catalytic Cathodic Stripping Voltammetry

Existing electrochemical methods for the determination of iron require long deposition times to determine low iron levels. Here a new method, based on catalytic cathodic stripping voltammetry, is described to determine subnanomolar levels of iron in seawater. The new method has a better baseline and is generally simplified, leading to a lower reagent blank and minimized sample handling compared to a previous catalytic method [1]. Optimized conditions include the addition of 20 μM 1-nitroso-2-naphthol (NN), 40 mM bromate, and 0.01 M HEPPS pH buffer, giving measurements in pH 8 seawater. The detection limit is 0.08 nM Fe after an adsorption time of 30 s; the detection limit is lowered by increasing the adsorption time. The method can also be used to determine the redox speciation of iron: FeIII is determined specifically by masking FeII with 2,2-bipyridyl (Bp). The concentration of FeII can then be calculated by difference from the total iron concentration.