Extract of oak bark as a selective natural reagent for the spectrophotometric determination of iron (II) in pharmaceutical preparations and blood serum

Spectrophotometry is widely favored for iron detection due to its simplicity, speed, cost-effectiveness, and versatility. Conventional methods rely on synthetic chromogenic reagents, which often involve toxic chemicals, hazardous solvents, and significant waste generation. Natural plant extracts offer a sustainable solution, being less toxic, easier to prepare, and more environmentally benign than synthetic counterparts. This study introduces a simple, green, and cost-effective spectrophotometric method for iron determination using oak bark extract as a natural, selective reagent. The approach relies on the development of a reddish-brown colored complex (ëmax = 550 nm) when iron ions react with oak bark extract in a neutral acetate buffer solution (pH 7.0). Under optimized conditions, the assay demonstrated excellent linearity in the range of concentrations 0.56 – 5.6 ìg/mL (R2 = 0.998) with high molar absorption coefficient (0.55 × 104 L/mol/cm), good sensitivity (LOD = 57.4 ng/mL, LOQ = 191.5 ng/mL), and precision (RSD < 5%). Statistical validation through t-test and F-test comparisons with 1,10-phenanthroline method confirmed the accuracy and reliability of the proposed method at 95% confidence levels. The assay showed remarkable selectivity for Fe (II) against various interfering cations. The proposed method was successfully applied for iron determination in blood serum and various pharmaceutical preparations, with a high recovery rate ranging from 98.01 to 103.38%.