TY - JOUR
T1 - Effect of Electrospray Ionization Source Conditions on the Tautomer Distribution of Deprotonated p-Hydroxybenzoic Acid in the Gas Phase
AU - Xia, Hanxue
AU - Attygalle, Athula B.
N1 - Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/6/7
Y1 - 2016/6/7
N2 - The deprotonation site of p-hydroxybenzoic acid upon electrospray ionization has been a subject of fervent debate in several articles in the Journal of the American Chemical Society and elsewhere. General consensus is that electrospray ionization mass spectrometry (ESI-MS) experimental results reflect the situation in solution to a considerable extent. Our research, using ion-mobility mass spectrometry, challenges the notion that ESI-MS results directly reflect solution-phase structures and demonstrates that the relative populations of the thermodynamically less favored gaseous carboxylate tautomer or the thermodynamically more favored gaseous phenoxide tautomer, generated from the same aqueous solution of p-hydroxybenzoic acid by ESI, can be varied back and forth by changing the probe position, capillary voltage, desolvation-gas temperature, sample infusion flow rate, and cone voltage. In other words, solvent effects are not the primary criteria that determine the relative population distributions of tautomeric carboxylate (C-) and phenoxide (P-) ions (m/z 137) generated by electrospray ionization of p-hydroxybenzoic acid. In addition, we propose that the observed ratio of the P- and C- forms indirectly reflects the relative contribution of the charge-residue or ion-evaporation process that occurs during the electrospray ion generation process.
AB - The deprotonation site of p-hydroxybenzoic acid upon electrospray ionization has been a subject of fervent debate in several articles in the Journal of the American Chemical Society and elsewhere. General consensus is that electrospray ionization mass spectrometry (ESI-MS) experimental results reflect the situation in solution to a considerable extent. Our research, using ion-mobility mass spectrometry, challenges the notion that ESI-MS results directly reflect solution-phase structures and demonstrates that the relative populations of the thermodynamically less favored gaseous carboxylate tautomer or the thermodynamically more favored gaseous phenoxide tautomer, generated from the same aqueous solution of p-hydroxybenzoic acid by ESI, can be varied back and forth by changing the probe position, capillary voltage, desolvation-gas temperature, sample infusion flow rate, and cone voltage. In other words, solvent effects are not the primary criteria that determine the relative population distributions of tautomeric carboxylate (C-) and phenoxide (P-) ions (m/z 137) generated by electrospray ionization of p-hydroxybenzoic acid. In addition, we propose that the observed ratio of the P- and C- forms indirectly reflects the relative contribution of the charge-residue or ion-evaporation process that occurs during the electrospray ion generation process.
UR - http://www.scopus.com/inward/record.url?scp=84974533846&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84974533846&partnerID=8YFLogxK
U2 - 10.1021/acs.analchem.6b01230
DO - 10.1021/acs.analchem.6b01230
M3 - Article
AN - SCOPUS:84974533846
SN - 0003-2700
VL - 88
SP - 6035
EP - 6043
JO - Analytical Chemistry
JF - Analytical Chemistry
IS - 11
ER -