A novel NMR method for the determination and monitoring of evolution of hydrogen peroxide in aqueous solutions

Abstract

A novel NMR method that allowed the rapid and direct quantitative analysis of hydrogen peroxide in protic solvents was developed. The method was based on the highly deshielded (1)H NMR signal of the H2O2 protons (δ ∼ 11.15 ppm at 298 K) in H2O and the combined use of cryoprotective (antifreeze) mixtures of H2O-DMSO-d6, low temperatures (∼260 K), and pH effects in order to achieve minimum proton exchange rate and, thus, sharp (1)H line widths. Extremely broad resonances with line widths above 550 Hz at room temperature in H2O were observed in a wide range of pH values, which were reduced below 2 Hz with the use of the above method which resulted in a detection limit of 20.0 μmol L(-1) (in tube) even when using very short total experimental time of 10 min. The method was applied in aqueous extract of Greek oregano and in aqueous instant coffee. Line widths below 10 Hz for oregano samples and 17 Hz for instant coffee samples were obtained which resulted (i) in the unequivocal assignment of H2O2 with spiking experiments precluding any confusion with interferences from intrinsic phenolics in the extracts and (ii) in the quantitative investigation of the evolution of H2O2 in real time with parameters easily accessible experimentally.