Quantifying plasticizer leakage from ion-selective membranes - a nanosponge approach
Spontaneous process of release of plasticizers from membranes typically applied in ion-selective sensors is effect which limits lifetime of sensors and brings a risk of safety hazard. We use nanosponges approach to look at magnitude of this problem, quantifying the resulting contents of the plasticizer in solution. This novel method takes advantage of spontaneous partition of the plasticizer (released and present in solution) to nanoparticles loaded with a solvatochromic dye. As a result nanoparticles are transformed to capsules. This process is coupled with turn-on fluorescence intensity change of the dye embedded in nanostructures, proportional to analyte concentration in the ppm range; allowing insight into plasticizer contents in the solution. It was found that spontaneous release of plasticizer is dependent on its nature as well as presence of ionophore and ion-exchanger. For a typical ion-selective membrane composition the leakage effect results in up to 20 ppm of 2-nitrophenyl octyl ether found in solution after 12 h contact. On the other hand, for less polar plasticizer - bis(2-ethylhexyl) sebacate, although presence of ionophore and ion-exchanger also increases amount of compound released from the membrane, its concentration in solution does not exceed 2 ppm after 12 h. The herein presented conclusions can be important not only for designing robust sensors but also end-used safer ones. Results obtained for ion-selective membranes were equal within the range of experimental error with those obtained using liquid chromatography coupled with mass spectrometry (LC MS) approach, confirming high analytical potential of the nanosponge approach.