An Optimised 1,10-Phenanthroline Method for the Determination of Ferrous and Ferric Oxides in Silicate Rocks, Soils and Minerals

A precise, accurate and rapid method for the sequential determination of FeO and Fe2O3 in rocks, soils and some non-refractory minerals by 1,10-phenanthroline spectrophotometry is described. Fe(II) and Fe(III) were leached from the sample (-200mesh) using a mixture of NH4HF2 and H2SO4 at 40-80 degrees C for 10min on a hot plate. Both Fe(II) and Fe(III) could be conveniently estimated sequentially from the same reaction mixture at the gg-1 to percentage level. The method is better than the existing wet chemical methods, including the commonly used Pratt's titrimetric redox method, for Fe(II) and Fe(III) determinations in rock and soil samples in terms of precision, accuracy and rapidity. The throughput of the method was very high; at least forty to fifty samples could be estimated easily in a day. The results obtained compare favourably with those obtained by Pratt's method, as well as for certified/recommended values of a set of eleven certified reference materials having FeO and Fe2O3 contents in the range 0.21-14.63% and 0.58-8.48%, respectively. The optimised 1,10 phenanthroline method was found to be accurate to within 0.21% m/m FeO and 0.30% m/m Fe2O3 compared with the literature values of the certified reference materials studied.