The disclosure relates to a calcium complex of 10-(2,3-Dihydroxy-1-(hydroxymethyl)propyl)-1,4,7,10-tetraazacyclodecane-1,4,7-triacetic acid (Calcobutrol) prepared by a process comprising the steps: (a) the gadolinium complex of 10-(2,3-dihydroxy-1-(hydroxymethyl)propyl)-1,4,7,10-tetraazacyclodecane-1,4,7-triacetic acid (Gadobutrol) is de-complexed with a de-complexing agent, wherein the de-complexing agent is an oxalate ion source or a phosphate ion source and the pH before adding the de-complexing agent is higher than 2, (b) the precipitated gadolinium salt is removed, (c) the free ligand in the solution resulting from step (b) is bound to an acidic ion exchange resin, (d) said resin is eluted with an aqueous alkaline solution, (e) the eluate is treated with acidic ion exchange resin, and (f) the ligand is complexed with Ca2+ ions and crystallised. The disclosure furthermore concerns Calcobutrol with a high level of purity, which is used for the preparation of galenic formulations of Gadobutrol, wherein the calcium complex prevents the release of free gadolinium in the formulation (e.g. by storage for several years, re-complexation with foreign ions from the glass).
