Chemical Transformations Can Occur during DMS Separations: Lessons Learned from Beer's Bittering Compounds

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Separation Science

Background:

• Developing separation methods for beer's bittering compounds, specifically humulone tautomers, using drift-tube mass spectrometry (DMS).
• Observed partial resolution of argentinated humulone tautomers ([Hum + Ag]+) in a nitrogen environment with isopropyl alcohol (IPA).

Purpose of the Study:

• Investigate the loss of resolution for humulone tautomers when resolving gas was introduced into the DMS.
• Understand the role of IPA in dynamic clustering, microsolvation, and tautomerization during ion transit.

Main Methods:

• Collision-induced dissociation (CID)
• UV photodissociation spectroscopy
• Hydrogen-deuterium exchange (HDX)
• Ion mobility spectrometry (IMS) simulations

Main Results:

• Confirmed assignments of dienol, cis-keto, and trans-keto tautomers using CID, UVPD, and HDX.
• HDX indicated proton transfer stimulated by IPA-humulone ion clusters.
• IPA accretion led to stable microsolvated ions, affecting compensation voltage (CV).
• Microsolvation mediated dienol to trans-keto tautomerization during DMS transit.

Conclusions:

• The addition of IPA and subsequent microsolvation and tautomerization significantly impacted ion mobility separation.
• Disparities in CV response due to microsolvation caused peak coalescence for cis- and trans-keto humulone tautomers.
• Observed keto/enol tautomerization within an ion-mobility device, a novel finding.