The present invention provides a new chemical process, a new cassette configuration, and new software for the automated production of multiple batches of an [18F]-labelled compound on a single cassette. The invention allows one synthesizer in one hot cell to produce sequentially a plurality of batches of [18F]-labelled PET tracer in the same day. In particular, the present invention provides a novel arrangement useful for purifying two consecutive batches of a reaction mixture comprising an 18F-labelled compound.