NZ 599705 The disclosure relates to a process for the preparation of the calcium complex of 10-(2,3-dihydroxy-1-(hydroxymethyl)propyl)-1,4,7,10-tetraazacyclodecane-1,4,7-triacetic acid (Calcobutrol), wherein the process comprises the steps of: (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.
