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A large variety ol optical sensors based on thin plasticized PVC membranes have been realized In the past. The organic membrane (bulk optode) contains the analyte recognition molecule such as a selective neutral lonophore, a H+-set active chromolonophore, and lipophilic anionic sites. In order to Improve the lifetime of analytically relevant sensing layers, their active components are covalently Immobilized to the polymeric matrix. Different Ca2+-selectlve bulk optodes with mobile or fixed chromolonophores and anionic sites are characterized and discussed with respect to sensor behavior such as dynamic range, repeatability, response time, selectivity, and lifetime. In general, the response time Increases upon Immobilization of components owing to limited diffusion within the membrane phase, whereas the lifetime Is enhanced drastically by a hindered loss of membrane components into the sample.

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