The present invention is a process for separating a target protein (such as a recombinant protein produced in a cell culture) from a mixture containing the target protein and contaminants (such as cell culture contaminants), by contacting the mixture with a hydrophobic adsorbent comprising branched hydrocarbon functional groups in an aqueous salt solution and collecting the unbound flow-through fraction containing the target protein. In one embodiment, the hydrophobic adsorbent may be a branched alkyl functional group. In another embodiment, the branched alkyl functional group has from 3 to 8 carbon atoms. In another embodiment, the branched alkyl functional group is a tertiary carbon atom, such as tert-butyl.