layer weak ion exchange adsorber stack with polyallylamine ligands in which an artificial defect hole had been introduced compared to an intact stack on application of sulfuric acid a markedly earlier breakthrough is seen for the membrane stack with hole compared to the intact membrane stack breakthrough curves on non particulate weak anion exchange adsorbers with polyallylamine ligands on application of hydrochloric acid a membrane modified with polyallylamine prepared as described in wo2009 127285 a1 example 21 was installed in a housing and used as described in example 1 of this application the following steps were performed 1 rinsing of the adsorbent with 10 ml of a solution of 1 mmol l naoh in water 2 washing of the adsorbent with 40 ml of high purity water 3 application of a 10 mmol l hcl solution onto the adsorber 4 recording of the volume passed and the ph in the outflow by means of a flow cell for the ph fig3 shows the breakthrough curve of a 3 layer weak ion exchange adsorber stack with polyallylamine ligands in which an artificial defect hole had been introduced compared to an intact stack on application of hydrochloric acid a markedly earlier breakthrough is seen for the membrane stack with hole compared to the intact membrane stack breakthrough curves on strong cation exchange adsorbers with sulfonic acid ligands on application of sodium hydroxide solution a commercially available membrane of the sartobind u00ae s type a strong cation exchanger.