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. Fig.2
