MEASUREMENT OF NONIONIC SURFACTANTS
IN AQUEOUS ENVIRONMENTS
Henry H. Tabak, Research Biochemist
Robert L. Bunch, Chief
Treatment Process Development Branch
U.S. Environmental Protection Agency
Municipal Environmental Research Laboratory
Office of Research and Development
Cincinnati, Ohio 45268
In the last 20 years there has been an increasing production of synthetic nonionic surfactants which are gradually replacing the anionic and cationic detergents in the household
products. The emergence of the nonionic surfactants as one of the predominant detergents
prompted a concentrated effort to develop and evaluate analytical methods for quantifying
these compounds in biodegradation studies and in environmental monitoring. A method
was sought which would be applicable to a wide range of nonionic surfactant types, be
sensitive to trace levels of nonionics found in biodegradation and environmental samples,
have a high degree of intra- and interlaboratory reproducibility, have a capacity for large
number of samples and be amenable to automation. It was desirable to include in the
method, a surfactant concentrating step to isolate the surfactant from larger culture and/or
environmental samples in order to increase surfactant concentration to a level sufficient
for analytical determination.
The older analytical methods available in the 1960's contained serious deficiencies [1].
Wickbold [2] published a method for trace levels of nonionic surfactants which involved
isolation of nonionic surfactants by a sublation (foaming) procedure with the use of N2
gas. The surfactants were then precipitated with Dragendorffs reagent (barium-bismuth-
iodide solution) followed by potentiometric titration of the bismuth in the precipitate, to
quantitate the Dragendorffs active substance (DAS). An iodide-iodine complexation method
for nonionics was developed by Baleux [3].
Of the colorimetric techniques, the cobalt thiocyanate measurement in which the nonionic surfactant is determined by complexation with cobalt thiocyanate and subsequently
measured colorimetrically [4-7] has been successfully applied to biodegradation and environmental studies.
The Organization for Economic Cooperation and Development (OECD) in its initial
evaluation of the Wickbold Method, found the Wickbold sublation procedure an effective
and a relatively simple concentration step for sampling surface active agents [8]. The presence of foamable ionic surfactants, however, particularly in environmental samples, made an
ion exchange procedure a necessary step after sublation. Subsequently, OECD, in concentrating its efforts on the various quantitative determinations, chose to evaluate the acceptability of the cobalt thiocyanate colorimetric and bismuth iodide potentiometric responses.
The EPA initial studies were undertaken to compare the cobalt thiocyanate method and
the Wickbold bismuth iodide, potentiometric bismuth titration test methods for nonionic
surfactants, using fatty alcohol ethoxylate-10.6 moles ethylene oxide (E.O.), fatty alcohol
ethoxylate-30.7 moles E.O. and nonyl phenol-9 moles E.O. as substrates [9]. Subsequent
ring test studies, as part of OECD interlaboratory effort, tested the applicability of the
Wickbold analytical procedure for isolation and quantitation of polyoxyethylene, alkyl
phenol ethoxylates (APE's): nonyl phenol-6 moles E.O. nonyl phenol-10 moles E.O., nonyl
phenol-30 moles E.O., nonyl phenol-8 moles E.O. (Lissapol NX); fatty alcohol ethoxylate:
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