Methods, compositions, and systems related to preparing gaseous 18F- compounds for use in radiolabeling positron emission tomography (PET) tracer precursor compounds are disclosed. [18F]fluoride ions produced by conventional methods are converted by reaction with an acid anhydride having the formula: to a gaseous 18F-compound having the formula: wherein each R is independently a substituted or unsubstituted, straight chain or branched CrC4 alkyl group. The resulting gaseous 18F-compounds can be produced and stored in close proximity to the production location of the [18F]fluoride ions (such as within a cyclotron vault), or easily and efficiently transported long distances with minimal loss of-radioactivity. The gaseous 18F- compounds, which also can be readily trapped on solid-phase extraction media or in organic solvents such as acetonitrile, provide an alternative source of [18F]fluoride for use in the nucleophilic substitution reactions that are used to synthesize a large number of 18F-labeled PET imaging tracers, including 2- [18F]fluoro-2-deoxyglucose (FDG).