Water-soluble forms of colloidal MnO₂ were prepared by the chemical reduction of KMnO₄ with Na₂S₂O₃ under neutral aqueous condition. The as-prepared colloidal MnO₂ solution is dark-brown, transparent, stable, and possesses the maximum absorption peak at 375 nm and an average diameter of 40 nm. The as-prepared nano-colloidal MnO₂ was found to react with formaldehyde to generate weak chemiluminescence (CL) under acidic condition. The effects of more than 30 pharmaceuticals on the nano-colloidal MnO₂-formaldehyde CL system were tested. Pharmaceuticals including phenothiazines and aminoethanethiols were observed to enhance the CL signal significantly. The experimental conditions were well optimized and the analytical figures for five phenothiazines and four aminoethanethiols were presented. The method was validated by the analysis of perphenazine in tablets and chlorpromazine hydrochloride in swine feed. The CL reaction mechanism was discussed by the study of CL spectra, fluorescence spectra, UV-vis absorption spectra, and other experiments. All of CL reactions had the same maximum emission wavelength about 640 nm, which suggested that the CL emitter was independent of analytes. The CL signal was inhibited obviously by single-state oxygen scavengers, sodium azide and 1,4-diazabicyclo[2,2,2]octane, indicating that single-state oxygen dimer was the potential CL emitter for the present CL reaction.

Key words: chemiluminescence, nano-colloidal MnO₂, formaldehyde, analytical application