The 1,3-Dioctadecyl-1H-imidazol-3-ium Based Potentiometric Surfactant Sensor for Detecting Cationic Surfactants in Commercial Products

A low-cost and fast potentiometric surfactant sensor for cationic surfactants, based on the new ion-pair 1,3-dioctadecyl-1H-imidazol-3-ium-tetraphenylborate (DODI-TPB), is presented. The new cationic surfactant DODI-Br was synthesized and characterized by NMR, LC-MS, and elemental analysis, and was used for synthesis of the DODI-TPB ionophore. The DODI-TPB surfactant sensor was obtained by implementation of the ionophore in PVC. The sensor showed excellent response characteristics with near-Nernstian slopes to the cationic surfactants DMIC, CPC, CTAB, and Hyamine 1622. The highest voltage responses were obtained for DMIC and CPC (58.7 mV/decade of activity). DMIC had the lowest detection limit (0.9 × 10−6 M) and the broadest useful linear concentration range (1.8 × 10−6 to 1.0 × 10−4 M). An interference study showed remarkable stability. Potentiometric titration curves for the titration of cationic surfactants (DMIC, CPC, CTAB, and Hyamine 1622), with DDS and TPB used as titrants, showed sigmoidal curves with well-defined inflexion points and a broad signal change. The standard addition method was successfully applied with recovery rates from 98.9 to 101.2 at two concentrations. The amount of cationic surfactant found in disinfectants and antiseptics was in good agreement with the referent two-phase titration method and the surfactant sensor on the market. This new surfactant sensor represents a low-cost alternative to existing methods for cationic surfactant detection

Potentiometric Surfactant Sensor for Anionic Surfactants Based on 1,3-dioctadecyl-1H-imidazol-3-ium tetraphenylborate

As anionic surfactants are used as cleaning agents, they pose an environmental and health threat. A novel potentiometric sensor for anionic surfactants based on the 1,3-dioctadecyl-1H-imidazol-3-ium tetraphenylborate (DODI–TPB) ionophore is presented. The newly developed approach for DODI–TPB synthesis is faster and simpler than the currently used strategies and follows the green chemistry principles. The DODI–TPB ionophore was characterized by computational and instrumental techniques (NMR, LC–MS, FTIR, elemental analysis) and used to produce a PVC-based DODI–TPB sensor. The sensor showed linear response to dodecylbenzenesulfonate and dodecyl sulfate in concentration ranges of 6.3 × 10−7–3.2 × 10−4 M and 5.9 × 10−7–4.1 × 10−3 M, for DBS and SDS, respectively. The sensor exhibits a Nernstian slope (59.3 mV/decade and 58.3 mV/decade for DBS and SDS, respectively) and low detection limits (7.1 × 10−7 M and 6.8 × 10−7 M for DBS and SDS, respectively). The DODI–TPB sensor was successfully tested on real samples of commercial detergents and the results are in agreement with the referent methods. A computational analysis underlined the importance of long alkyl chains in DODI+ and their C–H∙∙∙π interactions with TPB− for the ionophore formation in solution, thereby providing guidelines for the future design of efficient potentiometric sensors