NOVELTY - Preparing (p1) a gaseous 18 fluoride-compound comprises contacting a composition comprising 18 fluoride ions with an anhydride (a1). The 18 fluoride-compound is (a2).    USE - The method is useful for preparing a gaseous 18 fluoride-compound used for labeling a positron emission tomography (PET) tracer precursor compound with 18 fluoride (claimed), in the nucleophilic substitution reactions to synthesize a large number of 18 fluoride-labeled PET imaging tracers, including 2-(18 fluoride) fluoro-2-deoxyglucose and in PET imaging.    ADVANTAGE - The method: produces gaseous 18 fluoride-compound that is easily and efficiently transported long distances with minimal loss of-radioactivity, and readily trapped on solid-phase extraction media or in organic solvents; is cost effective; replace more complicated, costly, and time-consuming transport and production methods associated with 18 fluoride-labeling of radiopharmaceuticals; exhibits greater efficiency of usage of the raw material 18 oxygen-enriched water; allows successful recycling of 18 oxygen-enriched water in easy and more cost-effective way; produces highly reactive radiofluorination agents at increased yields; simplifies the radiochemistry by eliminating the 18 fluoride dry-down step in the radiochemical synthesis; facilitates the conversion of gaseous fluoride to other gaseous products, or reaction in the gas phase to form non-gaseous 18 fluoride-products; exhibits ease of trapping and storing the gaseous 18 fluoride-compounds, thus enabling practical storage and use-on-demand and eliminating the need to run the cyclotron to make 18 fluoride isotope for each synthesis; exhibits lower maintenance costs for 18 fluoride delivery lines and valves; and produces anhydrous gaseous 18 fluoride-compounds that do not contain trace metal from the target.    DETAILED DESCRIPTION - Preparing (p1) a gaseous 18 fluoride-compound, comprises contacting a composition comprising 18 fluoride ions with an anhydride of formula (a1). The 18 fluoride-compound is of formula (a2).R = optionally substituted, straight or branched 1-4C alkyl, preferably -CH2F, -CH2Cl, -CHFCH3, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3) 2 or -C(CH3) 3.    INDEPENDENT CLAIMS are also included for:    (1) preparing (p2) a gaseous 18 fluoride-compound for labeling positron emission tomography (PET) tracer precursor compound with 18 fluoride from (18 fluoride) fluoride ions produced by a proton accelerator, comprising contacting a composition comprising (18 fluoride)fluoride ions with an acyl halide of formula (X1-C=O-R) (h1);    (2) the 18 fluoride-compound (a2), where R is not methyl;    (3) the composition for labeling PET tracer precursor compound with 18 fluoride, comprising (a2) and an organic solvent or a solid phase extraction cartridge on which the 18 fluoride- compound trapped;    (4) a system (s1) for producing a gaseous 18 fluoride-compound for labeling PET tracer precursor compound with 18 fluoride, comprising 18 oxygen-enriched target water, a proton accelerator configured to produce a beam of accelerated protons in contact with the target water at a target location, an anion-exchange resin in close proximity to the target location, a gaseous (18 fluoride)fluoride production apparatus comprising the additional hardware needed to produce the gaseous 18 fluoride-compound and a transport tube capable of transporting a gas produced on the surface of the ion exchange resin to another location; and    (5) a system (s2) for producing a gaseous 18 fluoride-compound for labeling PET tracer precursor compound with 18 fluoride, comprising a reagent delivery valve in communication with a source of 18 fluoride-fluoride and at least one precursor for reacting with the 18 fluoride-fluoride to provide a gaseous compound, a first bank including a first set of columns, where a selected one of the first set of columns reversibly coupled to the reagent delivery valve, a second bank including a second set of columns, where a selected one of the second set of columns reversibly coupled to the selected one of the first set of columns and an output selector valve reversibly coupled to the selected one of the second set of columns for recovery of the gaseous 18 fluoride-compound, where each of the first bank and the second bank are rotatable about an axis to couple any one of the first set of columns in the first bank with any one of the second set of columns in the second bank, and when each of the reagent delivery valve, the first bank, the second bank, and the output selector valve are coupled, a continuous fluid pathway is formed between the reagent delivery valve and the output selector valve.    X1 = I, Cl, or Br.