The potential of hyphenating thermogravimetry (TG) and soft photo ionisation mass spectrometry (EBEL-SPI-MS) for fundamental and applied research and material analysis has been demonstrated by a newly developed TG-SPI quadrupole MS coupling (TG-SPI-QMS). Thermal decomposition of three common plastics, polyethylene (PE), polystyrene (PS) and polyvinylchloride (PVC) has been studied. While the decomposition of PE and PS in inert atmosphere takes place in a one step process (main mass loss at about 490 and 420 A degrees C, respectively), PVC decomposes in a two step mechanism. The organic signature of the PE decomposition shows homologous series of alkenes and polyenes, while PS is forming mainly styrene mono- and oligomers. In the PVC decomposition, firstly hydrogen chloride (HCl) is eliminated in a hydro-dechlorination reaction (1st mass loss step: 285-305 A degrees C), this is accompanied by the emission of the carbon skeletons of small aromatics (predominately benzene and naphthalene). In the second step (2nd mass loss step: 490-510 A degrees C), the residual cross-linked polyolefin moieties decompose under release of heavily alkylated aromatics, including larger PAH. Chlorinated aromatics are formed only in trace levels.