Potentiometric sensor for polyethoxylated nonionic surfactant determination

Direct Potentiometric Study of Cationic and Nonionic Surfactants in Disinfectants and Personal Care Products by New Surfactant Sensor Based on 1,3-Dihexadecyl-1H-benzo[d]imidazol-3-ium

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.

A new Iodobismuthate Method with a Low Volume Filtration Device as a New Tool for the Determination of Microgram Oxyethylate Amounts

The standard procedure of non-ionic surfactant detection by using the Bismuth Active Substances method offers low sensitivity, precision and a high consumption of the reagents. A new spectrophotometric (λmax = 460 nm of the visible spectrum) iodobismuthate method was developed, which may be successfully used to determine the presence of non-ionic surfactants at microgram levels. The oxyethylates were precipitated with the modified Dragendorff reagent, filtered, dissolved and afterwards the spectrophotometric determination of the equivalent bismuth amount was carried out. Several key factors, which influence the results of the proposed oxyethylate determination method, were optimized. The consumption of chemical reagents was notably decreased and the sensitivity of the method increased significantly in comparison to the standard method of non-ionic surfactant determination.