Potentiometric determination of NTA, EDTA and DTPA in mixtures

Consecutive potentiometric determination of EDTA and NTA or DTPA and NTA is described. The method is based on the titration with iron(III) chloride at pH 4-5 in the presence of a small amount of ferroin and 1,10-phenanthroline which keeps the concentration of free iron(II) ions constant, thus making the potential dependent only on the free iron(III) concentration.