745 ISSN 1061-9348, Journal of Analytical Chemistry, 2017, Vol. 72, No. 7, pp. 745–750. © Pleiades Publishing, Ltd., 2017. Determination of Cationic Surfactants in Soil Samples by the Disulphine Blue Active Substance (DBAS) Procedure 1 Jakub Idkowiak a , Agnieszka Zgoła-Grześkowiak a , Bożena Karbowska a , Radosław Plackowski b , and Bogdan Wyrwas a, * a Institute of Chemistry and Technical Electrochemistry, Poznan University of Technology, Berdychowo 4, 60-965 Poznań, Poland b Institute of Chemical Technology and Engineering, Poznan University of Technology, Berdychowo 4, 60-965 Poznań, Poland *e-mail: bogdan.wyrwas@put.poznan.pl Received April 1, 2016; in final form, August 20, 2016 Abstract⎯A method for the determination of cationic surfactants in soil samples was developed and applied to a biodegradation study. Five different cationic surfactants (benzalkonium chloride, 1-dodecyl-3- methylimidazolium bromide, didecyldimethylammonium bromide, trihexyl(tetradecyl)phosphonium bro- mide and trihexyl(tetradecyl)phosphonium chloride) were selected for the study with the developed method upon extraction from soil samples with methanol. The samples were subjected to analysis as disulphine blue active substances using a visible spectrophotometer. The limits of detection for the proposed method ranged from 2 to 27 μg/g, which enabled the determination of cationic surfactants in soil samples. The results obtained in the biodegradation study were confirmed using liquid chromatography coupled with tandem mass spectrometry. Keywords: cationic surfactant, solid sample, disulphine blue active substance, liquid chromatography, mass spectrometry DOI: 10.1134/S1061934817070061 Surfactants are compounds which consist of a polar head-group and a long hydrophobic tail-group. They tend to adsorb at the interface i.e. between two liquids (aqueous solution–organic solution) or between aqueous solution and air/soil. The hydro- philic part of the surfactant molecule is always directed towards the aqueous phase. Thereby, these compounds are accountable for the decrease of surface or interfacial tension. They play a number of funda- mental roles in industry, mainly in cleaning and wash- ing processes, but they are also used as emulsifiers, softeners, suspension stabilizers, catalysts or com- pounds for adjustment of flow resistance [1–3]. Sur- factants can be classified into four different groups based on their form in aqueous solutions: anionic, cat- ionic, zwitterionic and nonionic. World production of surfactants is estimated at 12.7 mln tons per year, 75% of which are commodity anionic and nonionic surfactants. The total annual production of surfactants in Western Europe is 2 mil- lion tonnes (2013) [4]. Cationic surfactants are only a small part of this production, i.e. 229 000 tonnes (2013) [4]. Cationic surfactants contain a positively charged hydrophilic part e.g. ammonium, phospho- nium or sulfonium ion. This group has no wash activ- ity effect, but fastens the molecules to the surfaces where they might provide softening, antistatic, soil repellent, anti-bacterial or corrosion inhibitory effects. Their most typical applications are softeners and antistatic agents. However, because of their strong biological activity, cationic surfactants are often applied as disinfectants in cleaning processes (includ- ing industrial and home usage) or as herbicides sprayed directly on crops. Their antifungal properties were also proven, and therefore they are widely used as wood protection agents [2, 3]. During emergency situ- ations, such as serious outbreaks of avian influenza or foot and mouth disease, quaternary ammonium sur- factants are also used as disinfectants sprayed on humans, buildings and the equipment [5‒7]. Quaternary ammonium surfactants enter the envi- ronment and can bind to soil. Their leaching to water is possible but considerable amounts of these com- pounds can still be adsorbed on soil particles. Due to high biological activity, their biodegradation can be problematic, therefore, high concentrations of these compounds can be found in contaminated regions. Due to this reason, the determination of these com- pounds is an important task, as it enables studying contamination of different regions. 1 The article is published in the original. ARTICLES