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

The hydrolysis of dehydroascorbic acid (DAAH) at neutral pH and 27 degreesC was investigated by direct infusion electrospray ionisation ion trap mass spectrometry (ESI-MS). This approach permitted derivatisation and elution p rocedures 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 M Sn experiments. The relevant signal intensities changed with time and a mod el, based on the irreversible pseudo-first order HyDAA(-) --> HyDKG(-) conv ersion, fitted successfully the data obtained for dehydroascorbate. The kin etic constant of the process was (3.2 +/- 0.5) x 10(-2) min(-1). The influe nce of metal ion traces on the hydrolysis rate was also checked, performing experiments in the presence of EDTA, and was found to be negligible.