Determination of nitrilotriacetic, ethylenediaminetetraacetic and diethylenetriaminepentaacetic acids in sewage treatment plant and paper mill effluents

A method for the determination of nitrilotriacetic (NTA), ethylenediaminetetraacetic (EDTA) and diethylenetriaminepentaacetic (DTPA) acids in sewage treatment plant (STP) and paper mill effluents has been developed. The chelating acids were extracted by solid-phase extraction cartridges packed with strong anion-exchange resins and were eluted by a small volume of 16 M formic acid. After conversion into their l-propyl esters, the acids were quantified by gas chromatography using a nitrogen-phosphorus-selective detector and confirmed by GC-MS with a mass selective detector. At a pH of 3.5, the recovery of these acids varied from 83 to 104% in water and STP effluent samples fortified to levels from 1 to 1000 mu g/l. Based on a concentration factor of 100, the detection limit for these acids was 0.5 mu g/l. All three acids were found in STP effluents, although the concentrations were relatively low for EDTA (<100 mu g/l) and DTPA (<15 mu g/l) in most samples. In contrast, much higher concentrations (>1000 mu g/l) of NTA were observed for nearly all primary STP effluents. A large variation in the levels of these acids was observed in the paper recycling mill effluents collected. Although their concentrations were mostly <150 mu g/l, the levels of DTPA were very high (>2500 mu g/l) in the effluents obtained from two mills that use this chelating agent to remove metal ions. DTPA was not detected and the concentrations for NTA and EDTA were <11 mu g/l in the effluents collected from the non-recycling paper mills.