An improved method for concentrating viruses from large volumes of clean waters is described. It was found that, by acidification, viruses in large volumes of water could be efficiently adsorbed to epoxy-fiberglass and nitrocellulose filters in the absence of exogenously added salts. Based upon this finding, a modified version of our previously described virus concentration system was developed for virus monitoring of clean waters. In this procedure the water being tested is acidified by injection of N HCl prior to passage through a virus adsorber consisting of a fiberglass cartridge depth filter and an epoxy-fiberglass membrane filter in series. The adsorbed viruses are then eluted with a 1-liter volume of pH 11.5 eluent and reconcentrated by adsorption to and elution from a small epoxy-fiberglass filter series. With this method small quantities of poliovirus in 100-gallon (378.5-liter) volumes of tapwater were concentrated nearly 40,000-fold with an average virus recovery efficiency of 77%.

A simple procedure for the concentration and partial purification of enteroviruses from tissue culture harvests is described. After removal of acid-precipitating components with a cationic detergent, the detergent and most membranecoating components were removed by treatment with a cationic-exchange resin. The resin effluent was then acidified, and the virus was adsorbed to epoxyfiberglass membranes. Virus was then eluted with pH 11.5 glycine-NaOH buffer. Since this eluate contains no organic compounds to interfere with virus adsorption to membranes, the virus can be reconcentrated simply by acidifying the eluate and passing it through a smaller membrane than that used for the first concentration. As high as 500-fold concentrations can be achieved, with a high efficiency of recovery.

Cellulose nitrate membranes were used as one of the adsorbents in concentrating viruses from water. For adsorption to occur, salts were required. With increase in valency of salt, less salt was necessary for enhanced virus adsorption to membranes. Trivalent salts were more effective because they could be used at only 1% the concentration required for divalent salts. Thus, 0.5 mM AlCl 3 was as effective as 50 mM MgCl 2 . For testing 500 gal of water, only 0.24 kg of AlCl 3 was required in contrast to 20 kg of MgCl 2 . Virus could then be eluted from such membranes, having an area of 486 cm 2 , with 250 ml of p H 11.5 buffer. Lowering the p H of the eluate and adding AlCl 3 permitted the virus to be quickly readsorbed on a smaller cellulose membrane, i.e., 4 cm 2 . Virus for assay was eluted from the small membrane in 1 ml. This procedure has provided the basis for concentrating minute amounts of virus from large volumes of water.

An improved method for concentrating viruses from large volumes of clean waters is described. It was found that, by acidification, viruses in large volumes of water could be efficiently adsorbed to epoxy-fiber-glass and nitrocellulose filters in the absence of exogenously added salts. Based upon this finding, a modified version of our previously described virus concentration system was developed for virus monitoring of clean waters. In this procedure the water being tested is acidified by injection of N HCl prior to passage through a virus adsorber consisting of a fiber-glass cartridge depth filter and an epoxy-fiber-glass membrane filter in series. The adsorbed viruses are then eluted with a 1-liter volume of pH 11.5 eluent and reconcentrated by adsorption to and elution from a small epoxy-fiber-glass filter series. With this method small quantities of poliovirus in 100-gallon (378.5-liter) volumes of tapwater were concentrated nearly 40,000-fold with an average virus recovery efficiency of 77%.

Influenza virus hemagglutinin was shown to be acid resistant if precipitates which form during acidification are first removed. Adsorption of virus to precipitates formed during acidification may cause a virus to be described incorrectly as acid sensitive.