Chemiluminescence reactions with acidic potassium permanganate: a re-evaluation of the emitting species and new analytical applications

A broad red band of light is emitted when potassium permanganate reacts with a wide range of compounds in acidic solution. This reagent is particularly responsive to certain phenolic compounds, which we have exploited to develop new methods for the determination of antioxidants, neurotransmitter metabolites, adrenergic amines and other biomolecules of interest. The characteristic red luminescence from these reactions has been attributed to several different emitting species, but supporting evidence has not been conclusive. We have directly compared the laser-induced photoluminescence of manganese(II) chloride with the chemiluminescence from reactions with acidic potassium permanganate to confirm that the characteristic red emission from this widely-used reagent emanates from an electronically excited manganese(II) species. However, in many previous cases where permanganate was used in the presence of fluorescent compounds, e.g. enhancers or reaction products, energy transfer to the efficient fluorophore was proposed. We have also examined many reactions of this type and found that in most cases the same characteristic red emission was produced, but there were several notable exceptions.