Determination of iron(III)-iron(II) mixtures by differential-pulse polarography in solutions containing ammonium tartrate and a good buffer

Abstract

An investigation into the determination of Fe^III and Fe^II by differential-pulse polarography (DPP) has been carried out using supporting electrolyte solutions containing ammonium tartrate (0.10 M) and sodium chloride (0.15 M) and buffered by zwitterionic Good buffers from pH 5.4 to 8.2. At a low pH a high proportion of the analyte, Fe^III, was reduced to Fe^II, while at a high pH, trace amounts of oxidants converted the Fe^II into Fe^III. However, by carrying out a DPP scan in the cathodic direction in solutions buffered by 3-(N-morpholino)-1-propanesulphonic acid (MOPS)(0.10 M) or N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulphonic acid)(HEPES)(0.10 M) at pH 7.4, reasonably stable, well separated maxima corresponding to Fe^II oxidation and Fe^III reduction were produced. These maxima were considerably more stable than those of the previously reported method using pyrophosphate as a supporting electrolyte and form the basis of a more reliable method for the determination of Fe^III-Fe^II mixtures.