DETERMINATION OF FERROUS IRON IN NONREFRACTORY SILICATE MINERALS .1. AN IMPROVED SEMI-MICRO OXIDIMETRIC METHOD

Peters' oxidimetric vanadate method for the determination of Fe(II) in silicate minerals was investigated to see if improvements could be made in the accuracy, precision and speed of the analysis. Specific attention was given to the composition of the acid matrix used to dissolve the samples, incubation temperature and period, composition of the acid matrix during the titration step, titration endpoint indicator, calibration of Fe(II) standard, the manner of adding and quantifying the amounts of oxidimetric reagents, and potential interferences. As a result of the investigation, several improvements were made in the method, notably, sample dissolution at 60-degrees-C for 4 hr., gravimetric addition of redox reagents, a sharper titration endpoint, and use of the same container for the entire process. Application of the improved method to the analysis of Fe(II) in 5 geochemical reference samples (BCR-1, G-2, PCC-1, MICA-Fe and MICA-Mg) and 3 mica samples yielded very precise results (S.D. 0.01-0.04% FeO) and very good agreement with reference values.