Process for the purification of a polypeptide of interest by cation-exchange chromatography wherein a chemical compound is added in a concentration of at least 7 mM a) to an equilibration fluid of the cation-exchange matrix wherein the equilibration fluid is adjusted such that at least part of the chemical compound in the equilibration fluid binds to the cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix and/or b) to a loading fluid which is applied to the cation-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 cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix and/or c) to a washing fluid which is used to wash the cation-exchange matrix once the polypeptide of interest has bound to the cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix wherein the washing fluid is adjusted such that at least part of the chemical compound in the washing fluid binds to the cation-exchange matrix due to a charge that is opposite to the charge of the cation-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 cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix thereby increasing the amount of the polypeptide of interest bound to the cation-exchange matrix relative to the amount of one or more impurities bound to the cation-exchange matrix before the cation-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 7mM, wherein the chemical compound is selected from a list consisting of chemical structures with amino groups and/or cationic amino acid polymers, such as tetraethylene pentamine (TEPA), dipicolylamine, poly-lysine, poly-arginine and poly-histidine. a) to an equilibration fluid of the cation-exchange matrix wherein the equilibration fluid is adjusted such that at least part of the chemical compound in the equilibration fluid binds to the cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix and/or b) to a loading fluid which is applied to the cation-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 cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix and/or c) to a washing fluid which is used to wash the cation-exchange matrix once the polypeptide of interest has bound to the cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix wherein the washing fluid is adjusted such that at least part of the chemical compound in the washing fluid binds to the cation-exchange matrix due to a charge that is opposite to the charge of the cation-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 cation-exchange matrix due to a charge that is opposite to the charge of the cation-exchange matrix