Germicidal Disinfectant Concentrate

Formulation Wt.% Dowicide 1 antimicrobial 2.0 Dowanol DPM (or 1 1 PnB DPM) glycol ether 10.0 Dowfax 2A1 surfactant 1.0 Sodium dodecyl benzene sulfonic acid 1.0 Water B6.0 

SOURCE The Dow Chemical Co. Dowanol Glycol Ethers Formulas 

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Available Chlorine Test. The chlorine germicidal equivalent concentration test is a practical-type test. It is called a capacity test. Under practical conditions of use, a container of disinfectant might receive many soiled, contaminated instniments or other items to be disinfected. Eventually, the capacity of the disinfectant to serve its function would be overloaded due to reaction with the accumulated organic matter and organisms. The chlorine germicidal equivalent concentration test compares the load of a culture of bacteria that a concentration of a disinfectant will absorb and still kill bacteria, as compared to standard concentrations of sodium hypochlorite tested similarly. In the test, 10 successive additions of the test culture are added to each of 3 concentrations of the hypochlorite. One min after each addition a sample is transferred to the subculture medium and the next addition is made 1.5 min after the previous one. The disinfectant is then evaluated in a manner similar to the phenol coefficient test. For equivalence, the disinfectant must yield the same number of negative tubes as one of the chlorine standards. 

Whereas these preparations do not possess the high bacteriostatic activity of quaternary ammonium germicides, they have the alternate advantage of being rapidly functional in acid solution. In comparative experiments of several different disinfectants, the acid—anionic killed bacteria at lower concentration than five other disinfectants. Only sodium hypochlorite and an iodine product were effective at higher dilution than the acid—anionic. By the AO AC use dilution test, the acid—anionic killed Pseudomonas aeruginosa at 225 ppm. Salmonella choleraesuis at 175 ppm, and Staphylococcus aureus at 325 ppm (172). 

A very commonly used disinfectant is ethanol-water in neutral or, preferably, in acidic conditions. Aqueous ethanol displays its best germicidal efficiency at a concentration of 60 to 70%. However, the most commonly used concentration in industry is about 20%, because higher concentrations require specific explosion-proof facilities. At 20%, ethanol has no sporicidal effect, its effect on viral inactivation is only partial and it does not destroy pyrogens (it only tends to destabilize large molecular aggregates of lipopolysaccharide molecules). For these reasons, 20% ethanol can only be considered as a bacteriostatic agent. Mixtures of ethanol with bases or acids are somewhat more sporicidal, but are not sufficient to provide sterilization at short incubation times and low temperatures. 

The various influences on the efficacy of UV disinfection are compiled in Fig. 9-1 (cf Malley Jr, 2000). Primarily, the efficacy of UV disinfection depends on the germicidal fluence Ho=EoXt which is the product of fluence rate Eq and the duration time t of the irradiation (often called UV dose , Chapter 2.1) (see Sommer et al., 1998). Other key factors include the hydraulics and hydrodynamics of the UV reactor (Kreft et al., 1986), its geometry (FIGAWA, 1998, Hoyer, 1996), the number and type of UV lamps required (Loge et al., 1996), their temperature profiles with respect to a maximum fluence rate Eq (in the case of LP Hg lamps, cf Fig. 4-8), the water quality and its variability such as UV absorbance/transmittance (Bolton et al., 2001, Sommer et al., 1997), the water matrix, e.g. nitrate concentration, its potential for quartz fouling by inorganic constituents particularly iron ions and hardness (cf Chapter 8-2), the turbidity, the particle content (total sus-... 

Ethyl and isopropyl alcohols in concentrations of 50 to 70 percent by weight are often used. Alcohols are somewhat slow in their germicidal action, acting by denaturing proteins. However, they are effective disinfectants against lipophilic viruses. Adding 0.1 N HCl to the alcohol can increase virucidal activity. 

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