Kinetic and spectral studies of EHPG systems using chemi- and electrochemiluminescence methods

The systems containing EHPG, EHPG-OCH3 and EHPG-NH-Ac and Tb(III) ions were used to study chemiluminescence (CL) and electrochemiluminescence (ECL) processes. In the CL studies the Fenton system (Fe(II)/(III)-H2O2) was used as a source of reactive oxygen species (ROS). Kinetic CL curves and CL spectral distributions were recorded. On the basis of the results obtained, it was demonstrated that Tb(III) acted as a sensitizer. Similarly obtained CL decays in the systems of Fe(II)/(III)-EHPG (or its derivatives)-H2O2 and Fe(II)/(III)-EHPG (or its derivatives)-Tb(III)-H2O2, independently on the Tb(III) concentration, showed that the lanthanide ions did not influence the kinetics of the oxidation of EHPG (or its derivatives) in the Fenton systems. The CL intensity increased with the increasing concentration of Tb(III) ions, which were the main emitters in the reaction systems. Spectrophotometric and luminescent studies of the systems before and after the additions of hydrogen peroxide proved that the excitation of the lanthanide ion was a result of energy transfer from the excited products of the oxidation of EHPG or its derivatives to the uncomplexed Tb(III) ions. ECL was generated on the surface of a nonstructural modified aluminum electrode with the use of K2S2O8, H2O2 or KN3 as coreactants in aqueous solution. In these studies we employed Al electrodes covered with a 2-4 nm layer of Al2O3 doted with Tb(III) or Dy(III) ions. The electrodes were polarized using cathodic and anodic pulses of various amplitude and frequency. The relative ECL efficiencies were determined as a function of electric pulse parameters, electrolyte compositions and the thickness of barrier or porous layer of the Al2O3 electrode.