Titration of low levels of Fe2+ with electrogenerated Ce4+ Original Research Article

A fast and accurate method for the determination of Fe2+ (5 μM–100 mM) is based on a coulometric titration with an amperometric end-point detection. The titration is performed in the consecutive-monotonic mode, permitting a fast titration rate (about 20 s per titration). A large number of samples can be titrated (up to 20) in the same electrolyte, thus saving reagents and waste. Due to this fast rate oxygen does not have to be removed from the solution even at the lowest concentrations, since the rate of oxidation is low compared to the rate of the titration. The amperometric titration with a pronounced break at the end point is enabled only due to the total irreversibility of the Fe3+/Fe2+ couple in 3 M H2SO4. The potential for the titration is chosen at the midway of the oxidation and of the reduction iron waves. Due to the fact that at that potential no oxide is formed on the platinum indicating electrode, the response of the indicating system is fast. The coulometric cell is characterized by a great simplicity due to the use of the new principles of non-isolated mini-counter electrode. The interferences caused by using non-isolated counter electrode are circumvented by optimizing the size of the counter and of the generating electrodes.