Elimination of volatile chemicals in disinfectant evaluation procedures by freeze drying

Standard methods for the removal or inactivation of disinfectants from reaction mixtures are often unsatisfactory when dealing with high concentrations of particulate organic matter. A method employing freeze drying was developed to eliminate residual disinfectant activity from reaction mixtures. Following the addition of volatile chemicals to sterilized cattle slurry, samples were removed from the mixture, freeze dried, and the dried material was reconstituted with diluent containing Escherichia coli as the test micro-organism to determine if the volatile chemicals had been removed. Twelve chemicals and one commercial disinfectant (Virkon S) were evaluated at different concentrations. The chemicals selected were acetone, ammonium hydroxide, carbon tetrachloride, chloroform, dichloromethane, ethyl alcohol, formalin, hydrogen peroxide, isopropyl alcohol, peracetic acid, sodium hypochlorite and xylene. Eight chemicals, acetone, ammonium hydroxide, carbon tetrachloride, chloroform, dichloromethane, ethyl alcohol, isopropyl alcohol and xylene were removed by freeze drying. The remaining four chemicals and the commercial disinfectant, which were not removed by freeze drying, could not be evaluated by this method.