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 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) <2.30%, RSD for Fe(T) <1.75%). Finally, the accuracy of the method was assessed for four monomineral samples using the standard addition method, with recovery percentages of 95.74-104.69% and 95.07-104.56% being obtained for Fe(II) and Fe(T), respectively.