A study on the standardization of phenanthroline spectrophotometry for the determination of ferrous iron content in red layered sandstone

<p indent="0mm">In order to rapidly and efficiently measure the ferrous iron content in red layered sandstone for conveniently determining the degree of rock weathering, this study established a standardized phenanthroline spectrophotometric technique with the standardization of usages, concentrations, and procedures of relevant reagents (HF, H₂SO₄, o-phenanthroline, NH₄HCO₃, boric acid, acetic acid-ammonium acetate, etc.) involved in the analytical process. Using sandstone digestion effectiveness, spike recovery rates, and stability of ferrous iron absorbance as key indicators, single-factor experiments have been conducted on the reagent quantities and concentrations, reagent addition sequences, and water bath durations. Based on the experimental results, the optimal quantities and concentrations of reagents have been determined, and the applicability of the standardized method has been evaluated. The results show that there are significant differences in ferrous iron contents of red layered sandstones measured by using the phenanthroline spectrophotometric technique under various experimental conditions. The standardized method has detection limit of approximately <sc>0.08 mg/L,</sc> with spike recovery rates ranging from 89.04% to 100.8% for the Fe(II) analytical method and from 85.97% to 113.6% for the total iron analytical method, indicating the stability and reliability of the standardized method.