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

The cathodic electrochemiluminescence (ECL) of peroxydisulphate (S₂O₈^2?)–ciprofloxacin (CPF) system at a wax‐impregnated graphite electrode was studied. When CPF was absent, S₂O₈^2? was electrochemically reduced to sulphate free radical (SO₄^??), and dissolved oxygen absorbed on the electrode surface was reduced to protonated superoxide anion radical (HO₂^?). The HO₂^? was oxidized by SO₄^?? to produce molecular oxygen in both singlet and triplet states. Some of the singlet molecular oxygen (¹O₂) further combined through collision to be an energy‐rich precursor singlet molecular oxygen pair (¹O₂)₂. A weak ECL was produced when ¹O₂ or (¹O₂)₂ was converted to ground‐state molecular oxygen (³O₂). 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 (¹O₂)₂. The other emitting species was excited singlet molecular oxygen pair (¹O₂)₂*], which originated from the chemical oxidation of CPF by SO₄^?? and dissolved oxygen. Based on the stronger ECL phenomenon, an ECL method for the determination of either S₂O₈^2? 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.