On-line spectrophotometric determination of ferrous and total iron in monominerals by flow injection combined with a Schlenk line-based digestion apparatus to exclude oxygen

•An automatic on-line method was proposed for the determination of both ferrous iron and total iron contents in monominerals.•A Schlenk line was used to provide an inert atmosphere to prevent oxidation of the ferrous iron during digestion.•Customized digestion vessels and heating plates were used to dissolve the samples and dilute the digestion solution in situ. An on-line photochemical method for measuring the ferrous iron [Fe(II)] and total iron [Fe(T)] contents in monominerals is described herein. A special digestion apparatus connected with a Schlenk line was designed to exclude oxygen during sample digestion. Subsequently, a spectrophotometric flow injection analysis (FIA) system was employed to automate the determination. As a result, a facile, reliable, and accurate analytical procedure was obtained, and both the sample and reagent consumption were reduced compared with traditional spectrophotometric procedures. In addition, the concentrations of the reductant and the chromogenic agent were optimized along with the sample leaching conditions (e.g., the amounts of H2SO4 and HF). Furthermore, the method precision was assessed by comparing the obtained results with those of four geological reference materials (relative standard deviation (RSD) for Fe(II)