Process for the purification of a polypeptide of interest by anion-exchange chromatography wherein a chemical compound which has the ability to complex one or more metal ions is added in a concentration of at least 7 mM a) to an equilibration fluid of the anion-exchange matrix wherein the equilibration fluid is adjusted such that at least part of the chemical compound in the equilibration fluid binds to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix and/or b) to a loading fluid which is applied to the anion-exchange matrix and which comprises the polypeptide of interest wherein the loading fluid is adjusted such that at least part of the chemical compound and at least part of the polypeptide of interest in the loading fluid bind to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix and/or c) to a washing fluid which is used to wash the anion-exchange matrix once the polypeptide of interest has bound to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix wherein the washing fluid is adjusted such that at least part of the chemical compound in the washing fluid binds to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix and that at least part of the polypeptide of interest and at least part of the already bound chemical compound if added at step a) or b) continue to bind to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix thereby increasing the amount of the polypeptide of interest bound to the anion-exchange matrix relative to the amount of one or more impurities bound to the anion-exchange matrix before the anion-exchange matrix is eluted and thereby leading to an increased ratio of the polypeptide of interest to one or more impurities in the eluate as compared to the same process wherein the chemical compound is added at a concentration of below 7 mM, wherein the one or more impurities comprise host cell proteins. a) to an equilibration fluid of the anion-exchange matrix wherein the equilibration fluid is adjusted such that at least part of the chemical compound in the equilibration fluid binds to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix and/or b) to a loading fluid which is applied to the anion-exchange matrix and which comprises the polypeptide of interest wherein the loading fluid is adjusted such that at least part of the chemical compound and at least part of the polypeptide of interest in the loading fluid bind to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix and/or c) to a washing fluid which is used to wash the anion-exchange matrix once the polypeptide of interest has bound to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix wherein the washing fluid is adjusted such that at least part of the chemical compound in the washing fluid binds to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix and that at least part of the polypeptide of interest and at least part of the already bound chemical compound if added at step a) or b) continue to bind to the anion-exchange matrix due to a charge that is opposite to the charge of the anion-exchange matrix