Proton-bound cluster ions in ion mobility spectrometry

Area of Science:

• Analytical Chemistry
• Physical Chemistry

Background:

• Ion mobility spectrometry (IMS) is a powerful analytical technique for gas-phase ion characterization.
• Understanding the formation and stability of protonated molecules, dimers, and trimers is key to interpreting IMS data.

Purpose of the Study:

• To investigate the influence of temperature and molecular properties on ion cluster formation in IMS.
• To identify factors governing the solvation and stability of protonated molecules and their aggregates.

Main Methods:

• Gaseous oxygen and nitrogen bases were introduced into an ion mobility spectrometer.
• Experiments were conducted at ambient and sub-ambient temperatures (-20°C).
• Mass spectrometry was used for ion identification and confirmation.

Main Results:

• At ambient temperature, protonated molecules, dimers, and hydrated ions were observed.
• Proton-bound trimers were generally not observed at ambient temperatures, even at high concentrations.
• Lowering the temperature to -20°C enabled the observation of both homogeneous and mixed trimers.
• Asymmetrical proton-bound dimers were observed in mixtures of oxygen bases but not always in oxygen-nitrogen base mixtures.

Conclusions:

• Operating temperature significantly impacts the degree of ion solvation and cluster formation in IMS.
• Hydrogen bond energy plays a critical role in the stability of observed ion aggregates.
• The dissociation of weakly bound dimers suggests a limited timescale for their observation in the IMS drift tube.