9 1 2 crib220u270rib220u18507i 1 _ 50 mM NaPi, pH 7.0 buffer + 1.35 M (NH<SUB>4</SUB>)<SUB>2</SUB>SO<SUB>4</SUB> (6 ml) to buffer (6 ml) _ Column chromatography hydrophobic interaction column chromatography (GE Healthcare UK Ltd., RESOURCE PHE)