Transcending Chromatography: Purification and Capture of Small Molecules via Preparative Mass Spectrometry

An ambient ion soft landing procedure is described. This new method enables ions of known mass/charge to be selected from the various species generated in an electrospray plume and to be soft-landed onto an ambient surface. Unlike the conventional ion soft landing which is performed in vacuum, here the ion generation, purification and collection all occur at atmospheric pressure. When combined with ambient ionization techniques such leaf spray (i.e., by applying a high DC voltage to an untreated leaf, endogenous substances present in the plant can be extracted and analyzed in-situ), ambient soft landing represents an efficient method for natural product discovery. The methodology will be demonstrated using pyrylium and imidazolium ions that typically ionize in electrospray ionization (ESI) to give predominantly one ionic species. In this particular experiments, ions derived from ESI are passed pneumatically through a heated metal drying tube, then ion polarity is selected using ion deflectors and the dry purified ions are soft-landed on the surface at a specified location determined by the electrodynamic forces involved. Charged micro-droplets can also be selected for collection by controlling the heat supplied to the drying tube. Under this conditions, accelerated chemical reactions have been observed for C-C and C-N bond formations. This has provided unique opportunities for small scale chemical synthesis in which intermediates for various natural products can be accessed. That ambient soft-landing operates at atmospheric pressure greatly increases the flexibility of the collection experiment as well as providing higher ion currents than available from conventional vacuum-based experiments.