The Ptolemy instrument is an Evolved Gas Analyser. Comet nucleus material, believed to be a frozen mixture of ices, dust and tar, will be collected by an Italian-supplied drill and delivered into a German-supplied oven. The ice sample is then heated to produce a gas mixture which passes into the Ptolemy instrument. The gas mixture is moved around the instrument using a series of valves, and is purified and processed using a set of chemical reactors. The gas will then be separated into its constituent chemical species using a gas chromatograph. Each chemical species is then analysed with regards to its isotopic composition using an ion trap mass spectrometer. These processes are illustrated below.