A system and method for separating ions in an ion mixture, such as a plasma in space. The ion mixture enters an electrostatic analyzer, whose ion path has at least two sections. A first section applies a DC voltage to the ions, and a next section applies an RF frequency voltage to the ions. Appropriate DC and RF voltages are applied, such that at least a portion of the lower mass ions are absorbed into the RF section of the analyzer. The heaver ions are transmitted out of the ion path and are readily available for further analysis.