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. Copyright © 2011 John Wiley & Sons, Ltd.