In previous work we have developed a dicarboxylate functionalized polymer that demonstrated chemical sensing. It showed good response to pH changes as well as to varying concentrations of copper and calcium ions. Our recent investigations showed interesting results upon testing the functionalized sensing polymer on heavy metals. This sensor is composed of microspheres of polyvinyl benzyl malonate lightly-cross-linked with divinyl benzene dispersed in a hydrogel membrane. The response of the

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... cal sensor is based on the interaction between the metal cations with the deprotonated functional group. The polymer, thus, undergoes shrinking as a result of neutralization of adjacent negative charges on the back-bone of the polymer. This causes significant changes in the optical properties of the sensing element. The optical changes were measured as absorbance vs. wavelength as the sensing membrane is exposed to solutions of varying concentrations of heavy metal ions. The sensor showed significant increase in absorbance up to a concentration of 5 × 10 -3 M to the following metal ions: Ni 2+ , Zn 2+ , and Cd 2+ . Furthermore, the studied capacity of the derivatized microspheres showed close values to Ni 2+ , Zn 2+ , Cd 2+ (1.20, 1.09, 1.08 mmol/g respectively). These kinds of properly functionalized polymers appear to be suitable, versatile sensing elements for the detection of low concentrations of heavy metal ions. In addition, all of the tested heavy metals showed a similar value of the equilibrium formation constant, (log K f1 is 2.63). In contrast, the sensor showed no significant response to varying concentrations of K + and Mg 2+ metal ions.