DETERMINATION OF DISSOLVED NONYLPHENOL ETHOXYLATE SURFACTANTS IN WASTE-WATERS BY GAS STRIPPING AND ISOCRATIC HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A method based on isocratic high performance liquid chromatography (HP LC) with u.v. detection at 229 nm was developed for the routine determ ination of dissolved nonylphenol ethoxylates (NPEOs) in waste waters. Gas stripping into ethyl acetate was chosen to extract and pre-concent rate the NPEOs after evaluation of a number of alternative procedures. The extract was cleaned-up by ion-exchange chromatography to remove c o-extracted anionic and cationic surfactants. This also removed the ma jority of non-surfactant contaminants arising from the sample matrix. Total NPEOs were determined from the single peak obtained on an octade cylsilica column using 90:10 methanol/water as mobile phase. The prese nce of an NPEO mixture in the extract was confirmed and oligomers with 4 or more ethoxylate groups determined using a cyanosilica column wit h 95:5 acetonitrile/water as mobile phase. Lower oligomers were determ ined on an octadecylsilica column with a higher carbon loading (10% or greater) using 98:2 acetonitrile/water as mobile phase. The recovery of NPEOs was better than 80% for most oligomers and for total NPEOs. A dsorption onto the filter paper is the major cause of losses. Recovery of the first oligomer was lower (60%); nonylphenol was not recovered at all and should be determined by an alternative method. Losses resul ting from incomplete extraction due to lesser surfactant properties ma y also be significant for these two species. For total NPEOs, the dete ction limit was 0.04 mg/l, accuracy was better than 80% and precision 4% or better. For individual oligomers, the detection limit was below 1 mu g/l. The procedure was shown to be applicable to the analysis of NPEOs in a variety of waste water samples containing significant physi cal and chemical interferences.