Collision induced dissociation of deprotonated glycolic acid

Glycolic acid has been recently found to be a contaminant in a drinking water sample from Canada. An in-depth study was conducted to establish a mechanism of the unique fragmentation patterns of deprotonated glycolic acid by using ion trap and Q-TOF tandem mass spectrometry. Tandem mass spectrometry information from analysis of isotopically labeled (13C and D) glycolic acids revealed two general dissociation pathways of glycolate. Major fragmentation patterns, initiated by nucleophilic attack of a negatively charged carboxylic oxygen on the α-carbon, proceed through an α-lactone intermediate ion and result in formation of glyoxalate, hydroxymethanolate, formate, and hydroxyl anions. The hydroxyl anion was detected as a species solvated by a molecule of water or methanol. Minor dissociation patterns originate from the initial proton transfer from the α-carbon to a negatively charged oxygen of the carboxylic group and lead to formation of hydroxymethanolate and hydrated hydroxyl ion. Proposed mechanisms of all fragmentation patterns of glycolate are presented in detail. Postulated gas phase dissociation reactions are described in terms of charge redistribution following collisional excitation. This approach has facilitated elucidation of the unique fragmentation pathways of glycolate and provided explanation for significant differences observed in dissociation of structurally similar hydroxycarboxylic acids.