DETERMINATION OF NON-IONIC SURFACTANTS

Abstract

High Performance Liquid Chromatography (HPLC) for the quantitative determination of

nonylphenol polyethoxylates (NPE) in wastewater is described. The ethoxy chain length distribution was

performed by normal phase HPLC using a UV detector. Two techniques for the isolation of APE from

wastewater were compared: gaseous stripping into ethyl acetate to extract the analytes from the samples,

and a column method. The mean values of influents and effluents were 1406 ~tg/L and 62 I-tg/L respectively.

The removal of NPE ranged from 92 to 97%. © 1997 Elsevier Science Ltd

Introduction

Polyethoxylated nonylphenols are important surfactants used commercially for many years as

emulsifiers and solubilizers in industrial processing, as well as household cleaning products. They have the

formula R - C6H 4- (OCH2-CH2)°OH, where R = C9H19 and n=6-18. They remain one of the largest volume

groups of non-ionic surfactants and have attracted a great deal of attention because of potential adverse

environmental effects. The highly branched nonyl group and the phenol ring of nonyl-phenol have been

shown in many studies to have only low to moderate biodegradability. Increasing toxicities were found with

decreasing polyethoxylate chain length.

Most detergents are discharged into municipal and industrial wastewaters. Certain surfactants can be

biotransformed to persistent and toxic metabolites during their degradation in sewage treatment. The nonionic

surfactants of the alkyl phenol ethoxylates exhibit this metabolic behavior. In addition to knowledge

of total concentration, information about the alkylphenol ethoxylates (APE) oligomer distribution is

essential in understanding the changes in APE, as it undergoes degradation and also in assessing the

environment impact of these changes.

The qualitative and quantitative analysis of these compounds using a system of titrimetric,

spectrometric and chromatographic techniques has been reported [1-5]. These procedures, however, are

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complicated and time-consuming, lack specificity and are subject to interferences. This was a reason to look

for a better method, which preferably should use only one analytical technique. Because of the

comperatively low volatility of the ethoxylated alkylphenols, a high-performance liquid chromatographic

(HPLC) approach seemed to offer the best solution, as HPLC has been recognized as a particular valuable

method for alkylophenol ethoxylates determination in environmental samples [1,5,7,8]. Normal phase

gradient elution HPLC separates ethoxylated alkylphenols according to their degree of ethoxylation.

The aim of the present work was the determination of the total concentration of NPE as well as the

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