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

The cathodic electrochemiluminescence (ECL) of peroxydisulphate (S(2)O(8)(2-))-ciprofloxacin (CPF) system at a wax-impregnated graphite electrode was studied. When CPF was absent, S(2)O(8)(2-) was electrochemically reduced to sulphate free radical (SO(4)(•-)), and dissolved oxygen absorbed on the electrode surface was reduced to protonated superoxide anion radical (HO(2)(•)). The HO(2)(•) was oxidized by SO(4)(•-) to produce molecular oxygen in both singlet and triplet states. Some of the singlet molecular oxygen ((1)O(2)) further combined through collision to be an energy-rich precursor singlet molecular oxygen pair ((1)O(2))(2). A weak ECL was produced when (1)O(2) or ((1)O(2))(2) was converted to ground-state molecular oxygen ((3)O(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 ((1)O(2))(2). The other emitting species was excited singlet molecular oxygen pair [((1)O(2))(2)*], which originated from the chemical oxidation of CPF by SO(4)(•-) and dissolved oxygen. Based on the stronger ECL phenomenon, an ECL method for the determination of either S(2)O(8)(2-) or CPF was proposed. The proposed ECL method has been applied to the determination of CPF in pharmaceutical preparations.