An electrospray ionization ion trap mass spectrometric (ESI-MS-MSn) study of dehydroascorbic acid hydrolysis at neutral pH

Abstract

The hydrolysis of dehydroascorbic acid (DAAH) at neutral pH and 27 °C was investigated by direct infusion electrospray ionisation ion trap mass spectrometry (ESI-MS). This approach permitted derivatisation and elution procedures to be avoided, reducing to the minimum extent sample manipulation and allowing a rapid and direct observation of the species involved in the reaction. Six main peaks, related to hydrated dehydroascorbate (HyDAA⁻) and diketogulonate (HyDKG⁻) anions, were observed in the mass spectra of DAAH solutions at different times of incubation and were characterised by MSⁿ experiments. The relevant signal intensities changed with time and a model, based on the irreversible pseudo-first order HyDAA⁻ → HyDKG⁻ conversion, fitted successfully the data obtained for dehydroascorbate. The kinetic constant of the process was (3.2 ± 0.5) × 10⁻² min⁻¹. The influence of metal ion traces on the hydrolysis rate was also checked, performing experiments in the presence of EDTA, and was found to be negligible.