Comets and asteroids are thought to be the main sources of interplanetary dust particles (IDPs). IDPs with a diameter < 50 um are able to survive the entry into the Earth's atmosphere, where they can be collected without destruction. Because of their small size and mass, typically <10 um and <10~^9 g, their chemical analysis iscdifficult. We introduce the proton microprobe for the
non-destructive detection of trace elemente in IDPs. Using the Heidelberg proton microprobe which provides a beam spot of < 2x3 um^2, four IDPs have been analyzed and up to 26 elements were detected. To quantitatively evaluate the proton-induced X-ray spectra we calculated ab initio Xray yields for the samples. Most elemental abundance ratios in three IDPs agree within a factor of two with those of cosmic abundance but with the notable exception of some volatile elements (P, Cu, Ga, Br, and Zn) which are strongly enriched. This is contrasting one IDP in which Ca and the volatile elemente K, Zn and S are depleted.