RATIONALE Plants emit a blend of oxygenated volatile C 6 compounds, known as green leaf volatiles (GLVs), in response to leaf tissue damage related to stress conditions. On-line chemical ionization mass spectrometry (CI-MS) techniques have often been used to study the dynamics of these emissions but they fail to selectively detect some important GLV compounds. METHODS A flowing afterglow tandem mass spectrometer (FA-TMS) was used to investigate the feasibility of selective on-line detection of isomeric hexen-1-ols and hexanal. Product ions at m/z 101 and 83 from chemical ionization (CI) of these compounds by [H 3O] +, and product ions at m/z 100, 99, 83, 82 and 72 from CI by [NO] +, have been subjected to collision-induced dissociation (CID) in the collision cell of the TMS at center-of-mass energies ranging between 0 and 9 eV. RESULTS CID of product ions at m/z 101 and 83 from CI of GLVs with [H 3O] + and of product ions at m/z 83, 82 and 72 from CI of GLVs with [NO] + resulted in identical fragmentation patterns for all measured compounds, ruling out any selectivity. However, CID of product ions at m/z 100 and 99 from CI by [NO] + led to CID product ions with abundances differing largely between the compounds, allowing the fast selective detection of 2-hexen-1-ols, 3-hexen-1-ols and hexanal with a chosen accuracy within a well-defined range of relative concentrations. CONCLUSIONS This research illustrates that, in contrast to common CI-MS techniques, FA-TMS allows the selective detection of hexanal in a mixture of hexanal and hexen-1-ols with a chosen accuracy for a well-defined range of relative concentrations and represents a step forward in the search for selective detection of GLVs in CI-TMS.