Abstract
A novel, simple, low-cost, and user-friendly potentiometric surfactant sensor based on the new 1,3-dihexadecyl−1H-benzo[d]imidazol−3-ium-tetraphenylborate (DHBI–TPB) ion-pair for the detection of cationic surfactants in personal care products and disinfectants is presented here. The new cationic surfactant DHBI-Br was successfully synthesized and characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectrometry, liquid chromatography–mass spectrometry (LC–MS) and elemental analysis and was further employed for DHBI–TPB ion-pair preparation. The sensor gave excellent response characteristics for CTAB, CPC and Hyamine with a Nernstian slope (57.1 to 59.1 mV/decade) whereas the lowest limit of detection (LOD) value was measured for CTAB (0.3 × 10−6 M). The sensor exhibited a fast dynamic response to dodecyl sulfate (DDS) and TPB. High sensor performances stayed intact regardless of the employment of inorganic and organic cations and in a broad pH range (2−11). Titration of cationic and etoxylated (EO)-nonionic surfactant (NSs) (in Ba2+) mixtures with TPB revealed the first inflexion point for a cationic surfactant and the second for an EO-nonionic surfactant. The increased concentration of EO-nonionic surfactants and the number of EO groups had a negative influence on titration curves and signal change. The sensor was successfully applied for the quantification of technical-grade cationic surfactants and in 12 personal care products and disinfectants. The results showed good agreement with the measurements obtained by a commercial surfactant sensor and by a two-phase titration. A good recovery for the standard addition method (98–102%) was observed.
Highlights
Licensee MDPI, Basel, Switzerland.Surfactants, or surface-active agents, lower the surface tension of water
The aim of this paper was to develop a novel direct potentiometric surfactant sensor The aim of this paper was to develop a novel direct potentiometric surfactant sensor based on the new 1,3-dihexadecyl−1H-benzo[d]imidazol−3-ium (DHBI) ionophore implebased on the new 1,3-dihexadecyl−1H-benzo[d]imidazol−3-ium (DHBI) ionophore implemented as a DHBI–TPB sensing material in a PVC-based sensing membrane
The results showed that the purity of the employed technical-grade surfactants varied from 95.39 to 98.45%, while benzalkonium chloride (BAC) and didecyldimehtylammonium chloride (DDAC) exhibited the lowest purity as expected
Summary
Surfactants, or surface-active agents, lower the surface tension of water. A surfactant’s basic structure is a charged, hydrophilic head and a “fat” hydrophobic tail [1]. Based on the charge of the head, they are divided into anionic, cationic, amphoteric and nonionic categories. Surfactants are widely used as washing and cleaning agents. The market size for surfactants was US$39.901 million in 2019 and is projected to reach US$52.417 million by 2025, at a compound annual growth rate (CAGR) of 4.5% between 2020 and 2025 [2]
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