Spectrophotometric Determination of Iron(Ⅲ) after Separation by Adsorption of its N-benzoyl-N-phenylhydroxylamine Complex on Naphthalene

The method is presented for the spectrophotometric determination of trace amounts of iron(Ⅲ) after separation by adsorption of the complex on microcrystalline naphthalene. Iron(Ⅲ) reacts with BPA to form a water-insoluble complex, which is easily adsorbed on microcrystalline naphthalene at room temperature. The mixture of complex and naphthalene is separated from aqueous solution and dissolved in dimethylformamide. The absorbance of the solution is measured at 437 nm against the reagent blank. Effects of pH, amounts of BPA and naphthalene, digestion time, standing time, shaking time and diverse foreign ions are studied. The molar absorptivity was 4.47 x 103 l.mol-l･cm-l , the sensitivity of the complex as expressed by the Sandell's notation being 1.25 x 10-2pg of copper per ㎠. Sample solution containing 50 μg of iron(Ⅲ) was analyzed ten times by the recommended procedure. The mean absorbance was 0.400 with relative standard deviation of 1.25%