The Determination of Parts per Million of Iron in Adipic Acid by Ultraviolet Absorption

Abstract

The near ultraviolet absorption of the FeCl₃ complex affords a convenient means of determining iron in adipic acid in the range 0.25–15 ppm

The use of a predominantly alcoholic solvent system obviates the necessity of carefully controlling chloride ion concentration.

Oxidation with H₂O₂ assures that all the iron is present in the ferric state.

The method may be extended to other alcohol soluble substances having sufficient transparency in the near ultraviolet.

High purity adipic acid (hexanedioic acid) must contain less than 3 ppm iron. Analysis for iron at this level by conventional colorimetric methods is not entirely satisfactory. The preliminary ashing of the sample is time consuming and there is an inherent lack of precision due to a high reagent blank.

Since adipic acid contains no chromophores which might give rise to near ultraviolet absorption, a direct spectrophotometric determination of iron was suggested in view of the intense absorbance of iron ion complexes.