Optimizing the Pratt-type titrimetric method to determine FeO in geochemical reference materials

Abstract

Copyright © 2020 by The Geochemical Society of Japan. values are validated by comparisons with the measured value of the reference materials. Among various types of wet chemical analyses, titrimetric methods are one of the most classical methods used to measure FeO values. Although titrimetric methods yield accurate FeO values, it is time consuming. Much progress has been made on measuring FeO using analytical instruments; this includes new methods such ion chromatography (Kanai, 1990; le Roex and Watkins, 1995), Mössbauer spectroscopy (Lalonde et al., 1998), phenanthroline spectrophotometry (Husler et al., 2011; Tarafder and Thakur, 2013), X-ray absorption near-edge structure (XANES) spectroscopy (Farges, 2001; Ohta et al., 2006; O’Neill et al., 2006, 2018; Berry et al., 2010, 2018; Cottrell and Kelley, 2011; Zhang et al., 2018), and electron probe microanalysis (EPMA) (Hughes et al., 2018; Li et al., 2019). In each of these developments, it is crucial to compare the results of unknown geological samples with geochemical reference materials; therefore, the importance of geochemical reference materials with certified values is increasing. The certified values of geochemical reference materials have previously been determined mainly by a titrimetric method. During this method, samples are first decomposed by sulphuric acid (H2SO4) and hydrofluoric acid (HF) in crucibles. They are then titrated with a potassium dichromate (K2Cr2O7) solution to allow volumetric calculation of the amounts of FeO. The difficulty arises Optimizing the Pratt-type titrimetric method to determine FeO in geochemical reference materials