Potentiometric determination of EDTA and NTA in detergents

A method is described for the potentiometric titration with iron(III) of EDTA and NTA in detergents, a platinum electrode being used as indicator. EDTA and NTA were extracted at pH 9 and 50–60 °C in the presence of magnesium(II). Interference from polyphosphates was minimized by hydrolysis to orthophosphate followed by remotion as magnesium ammonium phosphate. Complexometric titration was carried out at pH 4.7 in acetate medium, in the presence of ferroin. A preliminary cleaning of the platinum electrode with thiosemicarbazide in hydrochloric acid was found to improve significantly the potential measurements. A mean recovery of 93% for EDTA and 89% for NTA was observed.