The construction of a liquid nitrogen-cooled ion mobility spectrometer coupled
with time-of-flight mass spectrometry was implemented to demonstrate the ability to
discriminate between electronic isomers. Ion mobility allows for the separation of ions
based on differing cross-sections-to-charge ratio. This allows for the possible
discrimination of species with same mass if the ions differ by cross-section. Time-offlight
mass spectrometry was added to mass identify the separated peak for proper
identification.
A liquid nitrogen-cooled mobility cell was employed for a two-fold purpose.
First, the low temperatures increase the peak resolution to aid in resolving the separated
ions. This is necessary when isomers may have similar cross-sections. Second, low
temperature shortens the mean free path and decreases the neutral buffer gas speeds
allowing for more interactions between the ions and the drift gas. Kr2+ study was
performed to verify instrument performance.
The variable-temperature ion mobility spectrometer was utilized to separate the
distonic and conventional ion forms of CH3OH, CH3F, and CH3NH2 and to discriminate
between the keto and enol forms of the acetone radical cation. Density functional theory
and ab initio calculations were employed to aid in proper identification of separating
isomers. Monte Carlo integration tools were also developed to predict ion cross-section
and resolution within a buffer gas
