Investigations of photocrosslinked decyl methacrylate as a membrane matrix for electrochemical and optical ion and polyion sensors.
Ambrose, Theresa Marie
1998
Abstract
Exploration of novel membrane matrices is essential for the continued development and increased applicability of polymer membrane-based ion sensors. In this dissertation, decyl methacrylate (DMA) is established as a new membrane matrix for preparing potentiometric and optical ion and polyion sensors. Plasticized DMA membranes photocrosslinked with hexanedioldimethacrylate (HDDMA) and doped with appropriate ionophores can be used to prepare analytically useful potassium and carbonate ISEs. Such sensors display Nernstian response slopes, detection limits below 10 $\mu$M, and selectivity coefficients similar to those measured using typical PVC-based ISEs. When preparing sensors based on neutral ionophores selective for cations, endogenous anionic sites present within the membrane must be removed or compensated with cationic additives. DMA membranes of varying compositions can also be used to prepare polyion-sensitive electrodes. By decreasing the amounts of tridodecylmethylammonium chloride ion-exchanger, plasticizer, and crosslinker in the DMA membrane, the potentiometric detection limit for the polyanionic anticoagulant drug heparin is lowered to 0.04 $\mu$M. Since crosslinker molecules hold methacrylate backbone chains apart, interrupting interactions between the pendant decyl chains, ions and polyions diffuse more rapidly through highly crosslinked DMA films. Molecular imprinting strategies were used along with methacrylate derivatives of common ion carriers to prepare templated DMA-based sensors. Random covalent immobilization of these carriers within the membrane apparently prevents selective ion extraction, but represents a possible strategy to increase the lifetime of certain DMA-based ion sensors. DMA membranes can be covalently attached to glass substrates pretreated with methacryloyloxypropyltrimethoxysilane. Illustrating this feature, a solid-state potentiometric DMA-based sensing cartridge was used to detect clinically relevant levels of heparin in 50 $\mu$L whole blood. Robust and durable optical ion sensors can be prepared using covalently immobilized thin films of DMA containing pH-sensitive chromoionophores in addition to the appropriate ion carriers. Optical sensors for small anions and potassium display selective and reproducible responses with rapid 30 s response times. Highly crosslinked DMA-based polyion-sensitive optical films selectively detect heparin in undiluted human plasma. The structural versatility of DMA membrane films, demonstrated throughout this work, enables their use in improved sensing devices of the future.Subjects
Decyl Electrochemical Investigations Ion Matrix Membrane Methacrylate Optical Photocrosslinked Polyion Sensors
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