Multiplexed Charge Detection Mass Spectrometry for High-Throughput Single Ion Analysis of Large Molecules

Applications of charge detection mass spectrometry (CDMS) for measuring the masses of large molecules, macromolecular complexes, and synthetic polymers that are too large or heterogeneous for conventional mass spectrometry measurements are made possible by weighing individual ions in order to avoid interferences between ions. Here, a new multiplexing method that makes it possible to measure the masses of many ions simultaneously in CDMS is demonstrated. Ions with a broad range of kinetic energies are trapped. The energy of each ion is obtained from the ratio of the intensity of the fundamental to the second harmonic frequencies of the periodic trapping motion making it possible to measure both the m/z and charge of each ion. Because ions with the exact same m/z but with different energies appear at different frequencies, the probability of ion–ion interference is significantly reduced. We show that the measured mass of a protein complex consisting of 16 protomers, RuBisCO (517 kDa), is not affected by the...