Effect of ionic liquids on the kinetics and quantum efficiency of peroxyoxalate chemiluminescence in aqueous media

Abstract

Although the peroxyoxalate reaction is widely used in diverse analytical and bioanalytical applications, only a few mechanistic studies were published on this reaction in aqueous media. We report here a kinetic study on this reaction in aqueous borate buffer, in the absence and presence of imidazole-based ionic liquids (ILs). The ILs employed were 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4), 1-allyl-3-methylimidazolium chloride (AMICl) and 1-allyl-3-methylimidazolium acetate (AMIAc). The dependence of the emission intensity decay rate constants (kobs) on the hydrogen peroxide and borate buffer concentrations indicated that the reaction in this medium occurs by specific base catalysis and the reactive species is the hydroperoxy anion. The presence of the ILs results in an increase in the yields of singlet-excited states. In comparison, increasing the concentration of simple electrolytes, e.g., NaCl, tetra(n-butyl)ammonium chloride and acetate resulted in larger rate constants and smaller chemiluminescence quantum yields than those observed in aqueous buffer in the absence of these electrolytes. Correlation of the singlet quantum yields with the viscosity and empirical polarity of the aqueous IL solutions indicates that medium polarity is the more important parameter for chemiexcitation. In summary, our results indicate that the peroxyoxalate reaction can be conducted in essentially aqueous media; the presence of ILs increases the emission quantum yield, with a possible improvement in the detection limits of analytical applications.