Use of Ca+2 to re-aggregate lipopolysaccharide (LPS) in hemoglobin solutions and the subsequent removal of endotoxin by ultrafiltration

Divalent cations such as Ca⁺² can act as bridges between lipopolysaccharide subunits causing large vesicles to form. During a two-stage ultrafiltration Ca⁺² re-aggregated lipopolysaccharide subunits in protein solutions into large vesicles that could not pass a 300,000 nominal molecular weight cut-off ultrafiltration membrane. Such re-aggregation occurred at concentration ratio of hemoglobin Ao / lipopolysaccharide equal to or less than 17.0, or at concentration ratio of Ca⁺² / hemoglobin Ao / lipopolysaccharide equal to or greater than 8.5.