Pulsed acceleration charge detection mass spectrometry: application to weighing electrosprayed droplets

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Mass Spectrometry

Background:

• Accurate mass determination of macroions is crucial for understanding their properties.
• Existing methods may have limitations in range or precision for certain macroions.

Purpose of the Study:

• To introduce and validate a novel approach for measuring individual macroion masses.
• To investigate the size and charge characteristics of water droplets generated via different interfaces.
• To explore the role of aerodynamic breakup in electrospray ionization.

Main Methods:

• Utilized a pulsed acceleration tube situated between two image charge detectors.
• Recorded macroion charge and velocity before and after acceleration through a known voltage drop.
• Deduced macroion mass from charge and velocity measurements.
• Applied the method to water droplets from capillary and aperture interfaces.

Main Results:

• Successfully measured macroion masses in the 10(10)-10(14) Da range.
• Determined size and charge of water droplets, with aperture-interface droplets being ~10x smaller in mass.
• Observed low charges on droplets, especially from the capillary interface, often below the Rayleigh limit.

Conclusions:

• The described method provides a reliable way to measure macroion masses, extendable to lower mass ranges.
• Aerodynamic breakup significantly influences water droplet formation and charging during electrospray ionization.