To remove residual salt, the support material/adsorbent may be washed with an alcohol, in particular isopropanol or ethanol, preferably from 50 to 100% (v/v) alcohol or isopropanol or ethanol, particularly preferably from 60 to 90% (v/v) alcohol or isopropanol or ethanol, very particularly preferably from 65 to 85% (v/v) alcohol or isopropanol or ethanol.