Modified spectrophotometric methods for determination of iron(III) in leaves and pharmaceuticals using salicylic acid

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.