With the goal of increasing the mass range of sector-type mass spectrometers, a low-voltage ion source was designed and constructed. For secondary ions, produced by particle bombardment, the acceleration voltage can be as low as 1 kV, without seriously affecting the extracted ion currents. The extraction and focusing geometry in this low-voltage desorption ion source is studied by computer calculation of the fields and trajectories in the source. Measurements of the secondary Cs + abundances from a CsI sample as a function of the acceleration voltage are presented. Ion currents for organic ions desorbed from a glycerol matrix compare favourably with data from the literature for instruments using much higher acceleration voltages (6–10 kV). Cooling of the glycerol matrix reduces the losses of the matrix by evaporation, whereas the matrix properties are not affected. In this way, longer-lasting ion currents are obtained.