Claimed is a method for obtaining a radiopharmaceutical composition of 18F-1-amino-3-fluoro-cyclobutane-1-carboxylic acid (18F-FACBC) where said composition comprises； 50-100 mM citrate buffer and has a pH of 4.0-5.0 and wherein said method comprises: (i) reacting with a suitable source of [18F] a compound of formula (I) (where LG is a leaving group, PG1 is a carboxy protecting group and PG2 is an amine protecting group) to obtain a compound of wherein the leaving group has been replaced with 18F, (ii) removal of PG1, (iii) removal of PG2 to obtain crude 18F FACBC, (iv) carrying out a purification step comprising passing said crude product through a hydrophilic lipophilic balanced (HLB) solid phase to obtain 18F FACBC, (v) formulating said 18F-FACBC with citrate buffer. Preferably, the composition comprises 60-90 mM citrate buffer. Preferably, the composition has a pH of 4.1-4.5. Formula (I)
