Oxidative chemiluminescence of some nitrogen nucleophiles in the presence of formic acid as an ancillary reductant

Abstract

Chemiluminescence signals were obtained when aqueous propan-2-ol solutions of phenylhydrazine, 2-nitrophenylhydrazine, 4-nitrophenylhydrazine, 2,4-dinitrophenylhydrazine and hexanal oxime or aqueous solutions of hydroxylamine and dimethylglyoxime were injected into a carrier stream of formic acid which merged with acidified potassium permanganate solution. Rhodamine-B was present in the carrier stream as a sensitiser. The chemiluminescence was deduced to originate from the oxidation of the hydrazine or amine functional groups. For phenylhydrazine oxidation, dinitrogen was proposed as the emitting molecule; in the oxidation of hydroxylamine, a nitrogen oxide emitter was proposed. The role of the formic acid was as a source of formate ions, which are oxidised to carbon dioxide in a relatively slow reaction. It is further proposed that excited carbon dioxide molecules, as well as producing a feeble emission in what seems to be an autocatalytic reaction, transfer energy to the emitting products of analyte oxidation, thus enhancing their chemiluminescence. Injection of formate ions, or their massive production by injections of strong alkali, cause chemiluminescence signals which would interfere with those from the analyte. Iron salts, which catalyse the permanganate–formic acid reaction, have a similar effect but at much lower concentrations.