Abstract: The present invention relates to a process for purification of a target molecule, comprising the steps: (a) contacting a target molecule, and a population of target binding polypeptides (TBP), in solution for a sufficient time to allow complex formation; and (b) isolating the target from the complex from (a) by subsequent purification steps, wherein (i) the target binding polypeptides have at least two binding functionalities; a first binding functionality towards the target and a second binding functionality towards a catching ligand comprised in a solid support; and (ii) the first binding functionality comprises at least two binding sites for the target, and the target comp¬ rises at least two binding sites for the TBP.

Abstract: The present invention relates to a process for purification of a target biomolecule, comprising the steps: (a) contacting (i) a target biomolecule, (ii) a dual affinity polypeptide, and (iii) a solid support comprising a catching ligand, wherein the ratio between the equilibrium dissociation constants of the dual affinity polypeptide, [KD,t/KD,s], is at least 100 at standard conditions; and (b) recovering the target biomolecule by elution.