Extraction-spectrophotometric determination of iron(III) by means of quinaldic acid-N-oxide

Abstract

A simple and sensitive method for the determination of iron(III) is described. It is based on the extraction of the yellow-coloured complex of iron with quinaldic acid-N-oxide in chloroform. The absorption maximum is at 380 nm with molar absorptivity e380=1.03 · 104. Beer's Law is obeyed over the range 0.6–6 ppm iron with relative standard deviation of +-0.3% (Sandell sensitivity 0.005 μg/ml/cm2). The absorbance of the reagent blank is however high with consequent occasional disturbances, which are avoided when measured at 395 nm; molar absorptivity e395=7.4 · 103; effective concentration range 3–8 ppm iron with relative standard deviation +-0.5% (Sandell sensitivity 0.008μg/ml/cm2). A fairly large number of common ions do not interfere. Job's method of continuous variations and Asmus method indicate a iron-reagent ratio of 1∶3. Heterogeneous formation constant is KD=2 · 108.