Ion transport by viscous gas flow through capillaries

Area of Science:

• Analytical Chemistry
• Physical Chemistry

Background:

• Ion transport through narrow capillaries is critical for various analytical techniques.
• Understanding ion loss mechanisms is essential for accurate measurements.

Purpose of the Study:

• To investigate experimental parameters affecting ion transport efficiency in narrow capillaries.
• To model ion loss mechanisms, including space-charge expansion and diffusion.
• To compare ion transport from electrospray and corona ion sources.

Main Methods:

• Experimental study of ion transport using electrospray and corona ion sources.
• Development of a simple model for radial diffusional loss.
• Monte Carlo simulations to account for space-charge, turbulent flow, and velocity profiles.
• Analysis of transmitted ion current and ion mobility.

Main Results:

• Ion loss to capillary walls is significant, primarily due to space-charge expansion and diffusion.
• Simple diffusion models underestimate ion loss; Monte Carlo simulations provide better predictions.
• Corona ion source currents are well-reproduced by mobility values.
• Electrospray currents suggest a small fraction of current is carried by aerosol particles.

Conclusions:

• Ion transport efficiency is governed by complex interplay of diffusion, space-charge, and flow dynamics.
• Aerosol particle transport may contribute to electrospray ion currents.
• Wall charging in glass capillaries does not significantly alter ion current compared to metal capillaries.