Abstract A selected ion flow tube mass spectrometry (SIFT‐MS) study of the reactions of H 3 O + , NO + and O 2 + . ions with the ketones (M) 2‐heptanone, 2‐octanone, 2‐nonanone, 2‐undecanone and 2‐aminoacetophenone has been conducted in preparation for studies of volatile emissions from bacteria. The H 3 O + reactions all proceed rapidly via exothermic proton transfer, producing only MH + ions that form their monohydrates when water vapour is present in the helium carrier gas. The O 2 + . reactions proceed rapidly via dissociative charge transfer producing parent cations M + . and some fragment ions. The NO + reactions form the NO + M adduct ions at rates which are dependent on the pressure of the helium carrier gas. Combining the present NO + kinetic data with those available from previous SIFT studies, the phenomenon of charge transfer complexing is clearly demonstrated. This results in adduct formation in these NO + /ketone reactions at or near the collisional rate. SIFT‐MS spectra are presented to illustrate the simplicity of SIFT‐MS analysis of ketones using both H 3 O + and NO + precursor ions. Copyright © 2003 John Wiley & Sons, Ltd.