Electrospray-ionization mass spectrometry (ESI-MS) is a well-established tool for biotherapeutic analysis. It draws intact proteins or peptide ions into the vacuum of a mass spectrometer, where the ion mass is measured. Electrospray ion-mobility mass spectrometry (ESI-IMS) introduces ions into a low-pressure gas, where the effects of aerodynamic drag reveal their shape. This technique is just emerging as a valuable tool for characterizing intact proteins, even though for a decade it’s been the basis of a commercially available medical diagnostic test…