Ferric chloride flocculation for nonflocculating beef extract preparations

The addition of 2.5 mM ferric chloride to 0.5% beef extract solution at pH 3.5 was found to be highly efficient in the recovery of seeded poliovirus type 1 (Sabin) or indigenous viruses from environmental samples. This method was extremely useful to reconcentrate viruses from beef extract solutions that did not flocculate at pH 3.5.