Spectrophotometric determination of EDTA in aqueous solution through ferroin formation using sodium sulfite as the reducer.

This paper presents a simple, easy and reliable method for determination of EDTA (ethylenediaminetetraacetic acid) in aqueous system. Using EDTA chelating with ferric irons, an excessive amount of Fe(3+) was added to EDTA solution, and Fe(3+) in excess was reduced by addition of a Na2SO3 solution, the outcome ferrous ions were then reacted with 1,10-phenanthroline monohydrate (PTM) to form ferroin, a color developing reagent. The absorbance of the ferroin was determined using spectrophotometry, from which EDTA concentration was obtained. The method was tested for interferences and applied to determination of trace amount EDTA in its degradation by ozone oxidation, and the result compared with those from high-performance liquid chromatography. It was revealed that a low limit of 1.4μM for EDTA concentration detection was achieved with a high correlation coefficient of 0.999 combined with a low relative standard deviation of 0.6%. In contrast to all reported processes, where ferric ions in excess have to be separated from those chelated with EDTA prior to their reduction followed by interaction with PTM and spectrophotometric determination, the key merit of the present method is that EDTA concentration is determined without need of ferric separation, rendering the present process very easy. The method is also characterized by low cost, high precision and high reproducibility at the same time.