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