Cathodic electrochemiluminescence of the peroxydisulphate-ciprofloxacin system and its analytical applications

The cathodic electrochemiluminescence (ECL) of peroxydisulphate (S2O82-)ciprofloxacin (CPF) system at a wax-impregnated graphite electrode was studied. When CPF was absent, S2O82- was electrochemically reduced to sulphate free radical (SO4 center dot-), and dissolved oxygen absorbed on the electrode surface was reduced to protonated superoxide anion radical (HO2 center dot). The HO2 center dot was oxidized by SO4 center dot- to produce molecular oxygen in both singlet and triplet states. Some of the singlet molecular oxygen (O-1(2)) further combined through collision to be an energy-rich precursor singlet molecular oxygen pair (O-1(2))(2). A weak ECL was produced when O-1(2) or (O-1(2))(2) was converted to ground-state molecular oxygen (O-3(2)). When CPF was present, a stronger ECL was produced, which originated from two emitting species. The main emitting species was excited state CPF (CPF*), which was produced by accepting energy from (O-1(2))(2). The other emitting species was excited singlet molecular oxygen pair [(O-1(2))(2)*], which originated from the chemical oxidation of CPF by SO4 center dot- and dissolved oxygen. Based on the stronger ECL phenomenon, an ECL method for the determination of either S2O82- or CPF was proposed. The proposed ECL method has been applied to the determination of CPF in pharmaceutical preparations. Copyright (C) 2011 John Wiley & Sons, Ltd.