Process for the manufacturing of a gadolinium complex solution

A process for the manufacturing of a solution of the gadolinium complex of formula I

• wherein R is a C3-C12 hydroxyalkyl comprising at least 2 hydroxyl groups;
• comprising the following steps:
• i) providing a solution of a dimeric ligand of formula Ia
• wherein R is as defined above,
• ii) adding to the solution of the previous step a molar excess of gadolinium metal ions to complex the dimeric ligand provided in step i), whereby an intermediate solution comprising the gadolinium complex of formula I is obtained, and
• iii) adding to the intermediate solution of the previous step at least a precipitating agent selected from the group consisting of phosphate (PO43−), monohydrogen phosphate (1PO42-), dihydrogen phosphate (H2PO4-), orthophosphoric acid (H3PO4), oxalate (C2O42-), hydrogen oxalate (HC204-), and oxalic acid (H2C2O4) to precipitate a portion of free gadolinium metal ions as gadolinium salt, whereby a portion of free gadolinium metal ions precipitate as gadolinium salt and said solution of gadolinium complex of formula I is obtained,
• wherein the precipitating agent is added in an amount from 1.1 to 5 moles with respect to 1 mole of gadolinium metal ions within the intermediate solution.