Recently nonionic surfactants have found a wide application in various industrial fields, for example in production of synthetic detergents, drugs, foodstuffs et al. Synthetic surfactants is the mixtures of their isomers, homologues and oligomers. Therefore the quantitative identification and separate determination of them in complex liquids is a difficult analytical problem.

The potentiometric solid-state membrane sensors based on tetraphenylborate salt of the barium complex with poly(oxyethylated alkylphenols) were constructed for the detection of nonionic surfactant in various objects. For separation of homologous nonylphenol (NP) polyethoxylates a surface of poly(vinyl chloride) (PVC) plasticized membranes were modified by molecular PVC-sieves (nanofiltering membranes) with a controlled pore sizes. The different membrane compositions and pore generators were studied. They differed in polyethoxylate NPs with 10 or 100 ethylene oxide units (EOU) used in the membrane and sieve preparation. The main electrochemical characteristics of surfactant sensors with different membrane composition and sieve pore generators were determined. The electrode functions for the membranes work well in solutions of NP (1×10^-5 – 1×10^-2 M), the slopes being close to the theoretical ones for bivalent ions.

The separating power of nanofiltering membranes was examined at study of the transport processes (diffusion mass transfer) in a two-compartment cell (NP solution with a certain concentration against distilled water) with different molecular sieves between. The values of permeability coefficients and ion flows for nanofiltering membranes were calculated at the same time the NP concentrations in source-solution and pore generator sizes were varied. As the number of ethylene oxide units in nonionic surfactant increases, the said characteristics decrease as shown in Fig.1. Nanofiltering membranes let pass those NPs whose molecules are smaller or comparable in size with the pore generator; bigger ions are retained therefore the express step-down motion of permeability coefficients and ion flows are observed.

The application of nanofiltering membranes improves the selectivity of nonionic surfactant sensors and allows the separate determination of homologous nonylphenol polyethoxylates in mixtures.

1. POSTER: Nanofiltering membrane sensors for the determination of homologous polyoxyethylated nonylphenols, Microsoft Office Document, 0.3MB

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