Principles of Operation of a Rotating Wall Mass Analyzer for Preparative Mass Spectrometry

In this contribution, we describe the principles of operation of a rotating wall mass analyzer (RWMA), a mass-dispersive device for preparative mass spectrometry. Ions of different m/z are spatially separated by RWMA and deposited onto ring-shaped areas of distinct radii on a surface. We use a combination of an analytical equation for predicting the radius of the deposition ring and SIMION simulations to understand how to optimize the experimental conditions for the separation of multicomponent mixtures. The results of these simulations are compared with the experimental data. We introduce a universal mass calibration procedure, based on a series of polyacrylamide ions, which is subsequently used to predict the deposition radii of unknown analytes. The calibration is independent of the polarity, kinetic energy, and charge state of the ion as demonstrated by assigning m/z values of different analytes including multiply charged ubiquitin ions. We demonstrate that mass resolution of the RWMA is affected by the width and kinetic energy distribution of the ion beam. The best mass resolution obtained in this study is m/Δm = ∼20. Preparative mass spectrometry using RWMA provides the advantages of simplicity, compactness, and low fabrication cost, which are particularly promising for the development of miniaturized instrumentation. The results presented in this work can be readily adapted to preparative separation of a variety of charged species of interest to the broad scientific community.