A sample introduction system for a spectrometer comprises a desolvation region that receives or generates sample ions from a solvent matrix and removes at least some of the solvent matrix from the sample ions. A separation chamber downstream of the desolvation region has a separation chamber inlet communicating with the desolvation region, for receiving the desolvated sample ions along with non-ionized solvent and solvent ion vapors. The separation chamber has electrodes for generating an electric field within the separation chamber, defining a first flow path for sample ions between the separation chamber inlet and a separation chamber outlet. Unwanted solvent ions and non-ionized solvent vapors are directed away from the separation chamber outlet. The sample introduction system has a reaction chamber with an inlet communicating with the separation chamber outlet, for receiving the sample ions from the separation chamber and for decomposing the received ions into smaller products.