Complex formation of lactic acid by atmospheric pressure chemical ionization

Abstract

Oligomers and polymers of lactic acid are generally synthesized through condensation reactions by dehydration at high emperature under catalysis. In the present work, ionization behaviors of lactic acid produced by atmospheric pressure chemical ionization were investigated. Influence of the sample concentration, the heating zone temperature, and the source fragmentor voltage on kinds and abundances of the product ions was examined. Complex formation of the product ions with neutral species was also investigated. Not only lactate, [M-H] À and its complexes but also ions of condended species, [nM-(n-1)H 2 O-H] À with n = 2-5, and their complexes were observed. The condensation reactions occurred in an aerosol state generated in the heating zone for evaporation. By increasing the concentration of lactic acid, abundances of the product ions were increased and the increase of larger ones was noticeable. By increasing the heating zone temperature, abundances of the product ions were decreased and the decrease of larger ones was remarkable. By increasing the source fragmentor voltage, abundances of small product ions were increased and those of the complexes, [nM-(n-2)H 2 O-H] À with n = 2-5, were significantly decreased. Complex formation of lactate with the neutral condensed species was more favorable than that of the condensed oligomer ions with a neutral lactic acid.The experimental results were explained by energies and structures of the product ions and neutral species obtained by theoretical calculations.

Ionization behaviors of nitrotoluenes and dinitrotoluenes by reactions with acetone‐related reactant ion

“…In APCI, the reactant ions generated from the solvent and eluent affect the ionization efficiency of the analyte because the product ions are formed by reactions with the reactant ions. When acetone is used as a solvent or eluent, typical reactant ions of [2Acetone + H] + and [2Acetone + O 2 ] •− are produced in the positive and negative ion modes, respectively, which support analyte ionization 35–43 . Dichloromethane is a good solvent for ionization of TNT in APCI‐MS, 26 but any NT‐ and DNT‐related ions were not observed in APCI‐MS when using dichloromethane as solvent and eluent.…”

“…When acetone is used as a solvent or eluent, typical reactant ions of [2Acetone + H] + and [2Acetone + O 2 ] •À are produced in the positive and negative ion modes, respectively, which support analyte ionization. [35][36][37][38][39][40][41][42][43] Dichloromethane is a good solvent for ionization of TNT in APCI-MS, 26 but any NT-and DNT-related ions were not observed in APCI-MS when using dichloromethane as solvent and eluent. In the present work, types of the NT-and DNTrelated ions produced when using acetone as solvent and eluent were compared, and their ionization efficiencies were examined.…”