Determination of Collisional Cross Section Using Microscale High-Field Asymmetric Waveform ion Mobility...

Area of Science:

• Analytical Chemistry
• Physical Chemistry

Background:

• Collisional cross sections (CCS) are key ion characteristics measured by ion mobility-mass spectrometry (IMS).
• Determining CCS in high-field asymmetric waveform ion mobility (FAIMS) devices is challenging due to ion heating.
• This study investigates predicting CCS using microscale FAIMS with known standards.

Purpose of the Study:

• To evaluate the potential of microscale FAIMS for determining collisional cross sections (CCS).
• To assess the accuracy of CCS determination for peptide ions using external calibration with standards.

Main Methods:

• Coupling an Owlstone ultraFAIMS spectrometer with an Orbitrap Exactive mass spectrometer.
• Utilizing tetraalkylammonium halides (TAAHs) and poly-DL-alanine oligomers as CCS standards.
• External calibration with poly-DL-alanine peptides for singly and doubly charged species to determine CCS accuracy for bradykinin and substance P.

Main Results:

• Excellent calibration correlations (R² = 0.99) were achieved for both TAAHs and poly-DL-alanine standards.
• Accurate CCS determination for bradykinin [M+2H]²+ (±0.5% difference) at 250 Td.
• Substance P ions showed determination accuracy within ±5% ([M+H]⁺) and ±3% ([M+2H]²+), with decreased accuracy at higher dispersion field strengths.

Conclusions:

• Microscale FAIMS can determine CCS with reasonable accuracy, particularly for compounds structurally similar to the standards.
• Optimal accuracy for CCS determination was observed at dispersion field strengths of 240–260 Td.
• Accuracy is influenced by resolution from solvent adducts at lower fields and ion transmission at higher fields.