Determination of the solubility products of nitrilotriacetic acid, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid

A method is described for the determination of solubility products for polyaminopolycarboxylic acids. The neutral protonated species of NTA (nitrilotriacetic acid), EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid) were precipitated at low pH values. The amount of precipitate was quantified by gravimetry and complexometric titrations with a standard zinc(II) solution. The following solubility products were obtained: S-H3NTA = 10(-16.36) S-H4EDTA - 10(-24.66) and S-H5DTPA = 10(-30.43). Those values were used for theoretical calculation and optimization of the precipitation processes of NTA, EDTA and DTPA at different pH values in the absence and presence of the metal ions Fe3+ and Mn2+. (C) 1999 Elsevier Science B.V. All rights reserved.