During a Rendezvous-type cometary mission it will be possible to collect dust particles on exposed surfaces. A secondary-ion-mass-spectrometer is proposed for the subsequent chemical investigation of such dust collections. An ion gun shoots inert gas or oxygen-ions onto the sample. The energy of these primary ions can be chosen between 1 and 5 keV. The positive and negative secondary ions emitted from the dust surfaces are then analysed with a quadrupole mass filter. The mass range of the instrument will be 1-150 amu. The sensor is able to measure (a) nearly all elements in this mass region, (b) molecules and organic components present in the dust, (c) isotopic ratios of interesting elements. Results of a first series of simulation studies are reported.