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 Fe 2 O 3 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 (−200 mesh) using a mixture of NH 4 HF 2 and H 2 SO 4 at 40–80 °C for 10 min on a hot plate. Both Fe( II ) and Fe( III ) could be conveniently estimated sequentially from the same reaction mixture at the μg g −1 to percentage level. The method is better than the existing wet chemical methods, including the commonly used P ratt'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 P ratt's method, as well as for certified/recommended values of a set of eleven certified reference materials having FeO and Fe 2 O 3 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 Fe 2 O 3 compared with the literature values of the certified reference materials studied.