Fabrication and Evaluation of Calcium Ion Releasing Electrochemical Device Using a Ternary Complex

Abstract

The Ca²⁺ -release device was a carbon paste electrode including a ternary complex consisting of poly(vinyl sulfate) ion (PVS⁻), 11-ferrocenylammonium ion trimethylundecyl (FeTMUA⁺), and Ca²⁺. The ternary complex was characterized by potentiometric titrations. The potentiometric colloidal titration of PVS⁻ with FeTMUA⁺ using a surfactant electrode indicated that the potentials in the titration curve sharply increased at the equivalent point, and then the complexation was strong. The potentiometric titration of PVS⁻ with Ca²⁺ using a Ca²⁺-selective electrode had no significant endpoint because of weak complexation. The binding behavior of Ca²⁺ with PVS⁻ was independent of the co-existence of FeTMUA⁺. The carbon paste electrode (CPE) including the ternary complex was characterized by cyclic voltammetry. The peak of the oxidation wave of FeTMUA⁺ was observed at 800 mV (vs. saturated Ag/AgCl), which was larger than the oxidation potential of FeTMUA⁺ adsorbed on CPE from an aqueous solution. The release amount of Ca²⁺ was evaluated by atomic adsorption spectroscopy. After electrolysis, the release amount of Ca²⁺ increased with the content amount; the high content CPE released Ca²⁺ even without electrolysis, but the low content CPE did not release a significant amount without electrolysis. At last, a Ca²⁺ release electrochemical device was fabricated; a thin end (φ 0.5 mm) of a polypropylene tip was stopped with the CPE and a Pt wire inserted into the CPE. The slight amount of Ca²⁺ released from the limited area of the tip was monitored by a CCD Ca²⁺ image sensor. The released amount of Ca²⁺ increased with the electrolysis time only just under the tip, while the other area had no significate change of Ca²⁺. The small device can locally release Ca²⁺ to only a limited area. In addition, the analysis of the image sensor displayed that the Ca²⁺ release of the device was a two-stage discharge: in first stage Ca²⁺ released from the surface, and in second stage a large amount of Ca²⁺ was released independent of electrolysis. The CCD Ca²⁺ image sensor was very useful to characterize the Ca²⁺ release device.