Optimization of a Digital Mass Filter for the Isolation of Intact Protein Complexes in Stability Zone 1,1

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Physical Chemistry

Background:

• Digital mass filters offer advantages for large molecule analysis by isolating high mass-to-charge ratio (m/z) ions.
• Traditional methods require high radio frequency (RF) and direct current (DC) voltages, posing limitations.

Purpose of the Study:

• To investigate the impact of capacitively coupled digital waveforms on ion isolation in digital mass filters.
• To characterize the voltage offset and its effect on ion stability parameters (a value).
• To demonstrate the isolation of large protein complexes using these modified filter parameters.

Main Methods:

• Experimental determination of Mathieu stability diagrams for stability zone 1,1 with capacitively coupled digital waveforms.
• Analysis of voltage offsets introduced by capacitors, dependent on waveform voltage and duty cycle.
• Ion isolation experiments for single-charge states of protein complexes up to 800 kDa (GroEL).

Main Results:

• Capacitive coupling introduces a voltage offset, shifting the ion stability parameter 'a' from 0 to negative values (a < 0).
• This effect was demonstrated for isolating single-charge states of protein complexes, including GroEL (800 kDa).
• An isolation resolving power (m/Δm) of approximately 280 was achieved for an 800.5 kDa GroEL D398A ion (m/z 12,315, z = 65+).

Conclusions:

• Digital mass filters with capacitively coupled waveforms can effectively isolate high m/z ions of large molecules.
• The observed voltage offset and altered stability parameters are crucial for optimizing ion isolation.
• This technique facilitates the analysis of intact protein complexes, advancing proteomic research.