Abstract

Two simple, accurate, precise, sensitive, and pH-selective visible spectrophotometric methods have been developed
and validated for the direct estimation of iron(III) in pure form, leaves, and pharmaceuticals using salicylic acid
(SCA) as a chromogenic agent. The methods are based on complexation reaction between iron(III) and SCA at
pH 2.26 (±0.02) (Method A) and 6.1 (±0.02) (Method B) to yield chromogens with maximum absorption at 520
and 460 nm, respectively. Various factors to yield maximum absorption and sensitivity have been studied and
optimized. In both the methods, the absorbance was found to increase linearly with iron(III) concentration as
shown by the correlation coefficient (r) of 0.9999 and 0.9988 for Method A and Method B, respectively. The
calibration graphs are linear over the concentration ranges of 3.75-37.5 and 2.0-24.0 μg mL−1 in method A and
method B, respectively, with apparent molar absorptivity values of 1.71 × 103 and 3.01 × 103 L mol−1 cm−1. The
stoichiometry between iron(III) and SCA was found as 1:1 and 1:4 in Method A and Method B, respectively. The
methods were validated as per the current ICH guidelines. The methods developed were successfully applied to
determine iron(III) in curry and drumstick leaves, mustard seeds, and pharmaceuticals. The effect of interferents
such as cations, anions, and other organic substances was also studied.