Normal serums are lipid extracted to improve clarity, dialyzed against phosphate buffered saline (PBS) containing sodium azide, and freeze-dried. Normal serum diluted to 5% (v/v) in PBS is strongly recommended as a blocking agent to reduce background from non-specific, conserved-sequence, and/or Fc-receptor binding. Best results are obtained with diluted normal serum from the same host as the labeled antibody, as a separate incubation step before addition of the primary antibody.
Gamma globulins are further purified from non-immunized animal serums by salt fractionation, ion-exchange chromatography, and gel filtration. Gamma globulins are an inexpensive source of IgG with only trace amounts of other immunoglobulins and/or non-immunoglobulin serum proteins. Gamma globulins are supplied as sterile liquids in phosphate buffer without stabilizers or preservatives.