A method is described for production of a high purity compound of the formula (I) in crystalline form of the modification A. In this, starting from high purity gadobutrol, the gadolinium is removed by decomplexation with oxalic acid, and then with a calcium salt the calcium complex is produced in high purity. During the crystallization, a water equivalent of 9 - 11 weight % is set. The crystalline form of the modification A of the compound of the formula (I) is used in the production of Gadovist.本發明描述一種用於製備高純度式(I)化合物呈改質A之結晶型的方法。 在此方法中，以高純度釓布醇(gadobutrol)為起始物質，藉由用草酸解錯合來移除釓，及隨後用鈣鹽製備高純度鈣錯合物。在該結晶期間，設定9至11重量%之水當量。該式(I)化合物之改質A之結晶型用於Gadovist之製備中。
