Application of a New Potentiometric Sensor for Determination of Anionic Surfactants in Wastewater

Surfactants (surface active agents) are substances which incorporate a hydrophobic non-polar and a hydrophilic polar group, and have the tendency to accumulate at the phase boundary. This feature causes the wide application of surfactants. In 2012, the world surfactant market amounted to 27,040 million USD, and with average annual increase of 6.18 %, this amount in 2017 is estimated at 36,518 million USD2. ASs are used as components in cosmetic formulations, household products, industrial cleaners. Their wide application leads to water pollution, and thus endangers the flora and fauna3. The standard method for the determination of anionic surfactants (ASs) in wastewater is MBAS4 (Methylene Blue Active Substances), while twophase titration5 is used for determining AS in commercial products. Both standard methods have many drawbacks (use of carcinogenic organic solvents, difficulties in determination of anionic surfactants in turbid solution, the subjectivity of the person performing the analysis, inability of auto mation...). The limitations of the standard methods for the determination of AS impose the need for continuous development of new surfactant sensors, which are less expensive, miniaturized, easier to use. The Environmental Protection Act of Croatia does not allow the use of surfactants whose biodegradability is less than 90 %6, thus, the determination of low concentrations of AS in effluents is of great importance. Today, there are a number of techniques that are able to detect, identify, and quantify the surfactant in samples of a complex matrix7. The first methods for determination of ASs were developed from simple volumetric methods5, followed by spectrophotometric methods8,9, chromatography10–12, microfluidic techniques such as flow-injection analysis (FIA)13, capillary electrophoresys14, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR)15. The polymeric membrane ion-selective electrodes (ISEs)16–19 successfully replace standard methods for determination of ASs in various samples. ISEs are a simpler and cost-effective alternative to standard methods. ISEs have evolved from the coated-wire electrodes and liquid polymeric membrane electrodes containing ion-pair based sensing material. The widest use have found ISEs with PVC liquid membrane. Low concentrations of ASs can be determined by ISFET sensors20, biosensors21 or ISEs associated with FIA system. The aim of this study was the application of a newly developed screen-printed microsensor, based on dimethyldioctadecylammonium-tetraphenylborate (DDA-TPB) ion pair as a sensing material, for determination of ASs in industrial wastewater. Particular attention was paid to the determination of low concentrations of ASs. Application of a New Potentiometric Sensor for Determination of Anionic Surfactants in Wastewater