The field of instrumental monitoring of biogenic volatile organic compounds (BVOCs) is currently an important area of research in mass spectrometry. Present techniques allow off-line analysis of air samples (e.g. TD-GC/MS) whilst the available on-line techniques (proton transfer reaction mass spectrometry, PTR-MS) can quantify only the total concentration of several isomers of important non-methane BVOCs represented by mono- and sesquiterpenenes. The aim of the proposed project is to develop an analytical technique that will allow selective monitoring of individual isomers of mono- and sesquiterpenes in real time (