The present invention relates to a method of preparation of formulations of lanthanide metal complexes of macrocyclic chelators which further comprise a small excess of free chelator. The method uses a solid phase-bound scavenger chelator to remove excess lanthanide metal ions, prior to the addition of a defined excess chelator. Also provided is a method of preparation of MRI contrast agents, together with solid-phase bound chelator meglumine salts useful in the methods.
