Ion mobility spectrometer with radial collisional focusing

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Ion mobility spectrometry (IMS) is a powerful analytical technique for separating ions based on their size, shape, and charge.
• Traditional IMS instruments can suffer from excessive ion excitation, leading to reduced resolution and accuracy.
• Triple-quadrupole mass spectrometers offer versatile ion manipulation capabilities that can be adapted for IMS.

Purpose of the Study:

• To assemble and test a novel ion mobility spectrometer utilizing a 20-segment quadrupole as the mobility cell.
• To evaluate the instrument's performance in terms of ion excitation, transmission, and sensitivity.
• To measure collision cross sections for various ion types and compare them with existing data.

Main Methods:

• The instrument was constructed using a 20-segment quadrupole, functionally equivalent to the q2 region of a triple-quadrupole mass spectrometer.
• High helium cell pressure (up to 4 Torr) and a low axial electric field (20-160 V over 20.2 cm) were employed.
• Collisional focusing was utilized to enhance ion transmission efficiency.
• Collision cross sections were measured for atomic, cluster, peptide, and protein ions.

Main Results:

• The spectrometer design minimized internal ion excitation, even with applied RF and axial fields.
• Efficient ion transmission and good sensitivity were achieved due to collisional focusing.
• Measured collision cross sections for diverse ions were in good agreement with literature and theoretical values.

Conclusions:

• The developed 20-segment quadrupole ion mobility spectrometer is a viable and sensitive instrument for ion analysis.
• The combination of high pressure and low axial field effectively controls ion internal energy.
• This approach provides accurate collision cross-section measurements for a wide range of chemical species.