Determination of nonionic surfactants in water
Prof. Ing. Pavel Pitter, DrSc.
The theoretical part of this thesis summaries methods for nonionic surfactants determination, which are described in literature. There are methods for determination of nonionic surfactants total concentration, methods for identification of individual homologes and oligomers and methods for molecule structure specification.
The study of nonionic ethoxylates determination according to Czech standard ČSN ISO 7875, part 2 (Determination of nonionic surfactants using Dragendorff reagent – so-called BiAS method) is main subject of the experimental part. Three possible final determination of bismuth concentration are compared. The Bi content can be measured by potentionmetric titration with pyrrolidine dithiocarbamate, by atomic absorption spectroscopy or by ultraviolet spectrophotometry. Analogous method is given in the Standard Methods for Examination of Water and Wastewater. Nonionic surfactants react with cobalt thiocyanate reagent forming a Co – complex, in which cobalt concentration is determined by VIS spectrophotometry (CTAS method). The differences between BiAS and CTAS method are studied in this work.
The influence of ionic surfactants on nonionics determination is also demonstrated. The coexistence of less than 10-times larger amount of anionic surfactants (sodium dodecylsulfate) does not interfere, while the significant interference due to the presence of cationic surfactants (N–Septonex) is observed.
Both BiAS and CTAS method is not advisable for determination of alkyl ethoxysulfates. The concentration of these compounds can be measured by methods for anionic surfactants (for example by method with methylene blue).
Chromatographic behaviour of ethoxylated nonyphenol surfactants in reverse-phase systems using high-performance liquid chromatography is investigated. Ethoxylates are separated on C18 silica, eluted by acetonitrile / water and detected by fluorescence.
Nonionic and anionic surfactants concentrations are measured in influent and effluent of several Czech wastewater treatment plants and in sewage (the last part of this thesis).