The electrospray ionization tandem mass spectrometry (ESI-MSn) of L-ascorbic acid was studied using both positive and negative ion detection modes. Under the electrospray ionization conditions, L-ascorbic acid dissociated readily to form various characteristic fragments, which provided interesting insights into the organic chemistry of ascorbic acid. The effect of capillary temperature on fragmentation of L-ascorbic acid was experimentally investigated using multiple stage tandem electrospray ionization mass spectrometry. The mechanism of the degradation of L-ascorbic acid was discussed in detail based on the experimental collision-induced dissociation data recorded in these experiments, and was confirmed by the hy-drogen/deuterium exchange experiments.

Key words: electrospray ionization, degradation mechanism, tandem mass spectrometry, hydrogen/deuterium exchange, L-ascorbic acid