Higher Resolution Charge Detection Mass Spectrometry

Abstract

Charge detection mass spectrometry is a single particle technique where the masses of individual ions are determined from simultaneous measurements of each ion’s m/z ratio and charge. The ions pass through a conducting cylinder, and the charge induced on the cylinder is detected. The cylinder is usually placed inside an electrostatic linear ion trap so that the ions oscillate back and forth through the cylinder. The resulting time domain signal is analyzed by fast Fourier transformation; the oscillation frequency yields the m/z, and the charge is determined from the magnitudes. The mass resolving power depends on the uncertainties in both quantities. In previous work, the mass resolving power was modest, around 30–40. In this work we report around an order of magnitude improvement. The improvement was achieved by coupling high-accuracy charge measurements (obtained with dynamic calibration) with higher resolution m/z measurements. The performance was benchmarked by monitoring the assembly of the hepatitis B virus (HBV) capsid. The HBV capsid assembly reaction can result in a heterogeneous mixture of intermediates extending from the capsid protein dimer to the icosahedral T = 4 capsid with 120 dimers. Intermediates of all possible sizes were resolved, as well as some overgrown species. Despite the improved mass resolving power, the measured peak widths are still dominated by instrumental resolution. Heterogeneity makes only a small contribution. Resonances were observed in some of the m/z spectra. They result from ions with different masses and charges having similar m/z values. Analogous resonances are expected whenever the sample is a heterogeneous mixture assembled from a common building block.

Single-particle mass analysis of intact ribosomes by mass photometry and Orbitrap-based charge detection mass spectrometry

“…As such, this approach can overcome the challenges for analyzing highly heterogeneous biomolecular assemblies, for which—when measured by conventional native MS—individual charge states are often indistinguishable or extremely broadened, hampering accurate mass determination. Conventional CDMS approaches, including single-pass detection cylinder(s) and multi-pass ion trap-based detectors ( Keifer et al., 2017 ), exist already for several decades and have been successfully applied to studying of various biomolecules and polymers in the wide mass ranges ( Antoine, 2020 ; Keifer and Jarrold, 2017 ; Todd et al., 2020 ). Recently, the quantification and the appropriate calibration of induction image current for individual ions have enabled charge determination of single particles on commercially available Orbitrap mass analyzers ( Kafader et al., 2020b ; Wörner et al., 2020 ).…”

A Pandemic Early Warning System Decision Analysis Concept Utilizing a Distributed Network of Air Samplers via Electrostatic Air Precipitation

“…Recent innovations have revealed that CDMS can resolve the difference between a filled and unfilled capsid of a virus. [24]. The possible presence of a small amount of non-microbe material is not expected to affect morphological identification or chemical identification of a pathogen.…”

Frequency chasing of individual megadalton ions in an Orbitrap analyzer improves precision of analysis in single molecule mass spectrometry

“…The larger deviations (from the theoretical square root behavior) for the actual single ion intensities compared to the noise band suggest additional artifacts, rather associated with ion behavior than pure instrument performance. Beside sample heterogeneity in the HBV capsid assemblies 36 , these artifacts are most likely caused by the wide range of kinetic energies accepted by the Orbitrap as well as eccentric, non-circular orbits, both impacting the radial distance and thus the induced image current 37 .…”