An Improved Procedure for the Determination of Ferrous Iron Mass Fraction in Silicate Rocks Using a Schlenk Line-Based Digestion Apparatus to Exclude Oxygen

摘要

Precise and accurate determination of ferrous iron mass fraction in silicate rocks and geological reference materials is still a significant challenge due to the labile nature of the analyte. Here, we report a modified and improved procedure for the determination of ferrous iron mass fraction, capable of yielding moderately accurate and highly precise results in a relatively shorter time than before. This modified technique requires a more convenient operational procedure than the classical method. A sample digestion apparatus was designed that included a Schlenk line to expel air in order to prevent oxidation. The advantages of this procedure over the classical procedure are shorter process flow, higher efficiency and absence of an additional redox indicator. The composition of the acid matrix used to dissolve the samples as well as the incubation temperature and time was investigated. Comparative data for twenty-one reference materials are reported, with five of them reported for the first time by the Schlenk line procedure. A series of experiments were carried out to identify and minimise the main source of error. In addition, the possibility of eliminating the reducing substances before digestion, by pretreatment of the sample by cold 10% methanolic bromine, was also studied.