1.9.1. Chemical methods of sterilization and disinfection These chemical agents destroy any type of microbes with out showing any form of selectivity unlike antibiotics. The efficacy of these agents depends on the following factors. 1. Concentration of the agent There is a relationship between the concentration of the agent and the time required to kill a given fraction of the microbial population. Time of exposure Microbes are killed with a reasonable length of time with chemical agents. pH of the medium where action is to take place Hydrogen ion concentration determines degree of ionization of the chemical and bacterial surface charge. The non-ionized form passes through the membrane more readily than the ionized form. Temperature Bactericidal potency of the chemical agent increases with an increase in temperature. An increase in 100c doubles the bacterial death rate. Nature of the organism . Species of the bacteria . Growth phase of bacteria in culture . Presence of capsule, spore and other special structures . Number of bacteria in test system Presence of extraneous materials Organic materials like serum, blood or pus makes chemicals inert that are highly active in their absence. 2. 3. bacterial cell 4. 5. 6.