Determination of EDTA and DTPA as their Fe(III) complexes in pulp and paper mill process and waste waters by liquid chromatography

A method for analysing ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) was investigated to develop a liquid chromatographic (LC) method for the determination of concentrations of the aminopolycarboxylic acids EDTA and DTPA used as complexing agents in pulp and paper mills. All measurements were made using reversed-phase LC with UV detection. Ion-pairing reagent was added into the eluent to convert the interest of analytes into neutral compounds. Separation was performed using an ionic strength gradient, in which the increased proportion of phosphate buffer raised the ionic strength of the eluent. The concentration of methanol used as organic solvent and to wash the column was kept constant. The calibration curves for Fe(III)-EDTA and Fe(III)-DTPA were linear in the soluble range of the compounds in their acidic form up to 40 mg/dm³. The detection limit for both complexing agents was 0.5 mg/dm³. The repeatability (R.S.D.) was between 3-9% for Fe(III)-EDTA and 5-7% for Fe(III)-DTPA depending on the concentration. The method developed gives a good separation of the iron(III) complexes of EDTA and DTPA and enables monitoring the concentrations of EDTA and DTPA during pulping processes and waste water treatment.