A New Spectrophotometric Method for Determination of Iron in Herbs, Spices and Beans with 2,6-Diacetylprydine Dioxime and 2-Acetylpyridine Monoxime

Abstract

The reaction of iron (II) with 2, 6-diacetylprydine dioxime (H₂dapd) and 2-acetylprydine monoxime (Hapm) in 10% and 60% v/v ethanol-water solution at pH 2.5 and 7.5, respectively, were studied using direct and first derivative spectrophotometry. Fe (III) is reduced by H₂dapd and gives iron (II) complex. A simple, rapid, selective and sensitive method for the determination of Fe (II), Fe (III) and a mixture of them with the H2dapd reagent in acid water-ethanol medium after the solution attained to stand periods of 30 sec, 4 hr and 4 hr, respectively, are proposed. Hapm also reacts with Fe (II) to form [Fe(Hapm)₃]²⁺ complex with less selectivity and sensitivity than H₂dapm reagent. Calibration graph with [Fe(H₂dapd)₂]²⁺ is linear over the range 0.28 μg mL^ˉ1 with an apparent molar absorptivity of 8.481×10³ L mol^ˉ1cm^ˉ1 at λ_m 428 nm. Linear dynamic ranges are 0.01-11.0 and 0.07-11.0 μg mL^ˉ1 iron (II) as [Fe(H₂dapd)₂]²⁺ complex for direct and derivative modes, respectively. The analytical sensitivity is 4.44×10^-3 μg mL^ˉ1 for direct and 9.15×10^-5 μg mL^ˉ1 for derivative spectrophotometry with [Fe(H₂dapd)₂]²⁺ complex. First derivative method enhances the sensitivity of the Fe(H₂dapd)₂]²⁺ more than direct one with two folds for Ni²⁺, Co²⁺, Cu²⁺ and Cr³⁺. A linear equation was derived from iron (II) determining as Fe (H2dapd)₂]²⁺ in the presence of synthetic solution containing Ni²⁺, Co²⁺, Cu²⁺ and Cr³⁺. The use of H₂dapd reagent for the determination of total iron spectrophotometerically in foodstuffs, herbs, spices (rocks) after wet ashing (wet digestion) in the absence of reducing agent is compared with that employing AAS.