Application of Gas-Phase Electrophoresis (nES GEMMA Instrumentation) in Molecular Weight Determination

Gas-phase electrophoresis by means of a nano-Electrospray Gas-phase Electrophoretic Mobility Molecular Analyzer (nES GEMMA, also known as e.g., nES DMA, MacroIMS, or LiquiScan ES) separates singly charged, aerosolized (bio-)nanoparticles at ambient pressure in the gas phase according to the particle electrophoretic mobility (EM) diameter, i.e., an equivalent size related to spherical analytes. Corresponding size spectra in the range of a few to several hundred nanometers in terms of an EM diameter relate particle number concentrations to particle size values. Already shortly after the introduction of the instrument to the community of analytical chemists, its ability to yield particle molecular weight (MW) values based on measured EM diameters applying a corresponding correlation function was described. This first calibration function was solely based on protein monomers, dimers, and larger aggregates. In the following years, it became evident that this correlation function was well suited to calculate MW of globular proteins based on their EM diameters. For other substance classes, significant deviations were observed which ultimately led to the definition of further calibration functions. This manuscript reviews these developments and provides an overview of some key applications of gas-phase electrophoresis using the nES GEMMA system for MW determination of (bio-)nanoparticles from initial experiments in the year 1996 to the current day (2025).