The present invention is directed towards a process for manufacturing a complexing agent, said process comprising the steps of (a) Providing a nitrile according to general formula (I a) or (I b) With M being selected from alkali metal and hydrogen and combinations thereof, (b) Saponification with a total alkali amount of 2.5 to 2.9 mol of alkali metal hydroxide per mole of nitrile according to general formula (I a) or (I b), respectively, and a pH value in the range of from 9.5 to 11.5 at the end of step (b), (c) Adding an amount of alkali metal hydroxide so that the total alkali content is 2.9 to 3.15 moles per mole nitrile according to general formula (I a) or (I b), respectively, and (d) Allowing further conversion.