Final answer:
The chemical method not effective in the presence of organic matter and requiring 10-15 minutes of exposure is halogens, such as iodine. Quaternary ammonium compounds, in contrast, can disrupt bacterial membranes effectively.
Step-by-step explanation:
The chemical method that is not effective in the presence of organic matter (like dirty hands) and requires a 10-15 minute exposure time is halogens. Specifically, iodine, which is a type of halogen used in disinfectants, oxidizes cellular components and so requires a longer exposure time to be effective. Organic matter can shield microorganisms from the oxidizing action of iodine, thus compromising its disinfecting abilities. In contrast, quaternary ammonium compounds (quats) are cationic detergents that can infiltrate the phospholipid membrane of bacteria and disrupt their integrity, leading to cell death.
The effectiveness of disinfectants was historically compared to phenol. Phenol was the first chemical agent used by Joseph Lister, and the phenol coefficient was a measure to compare the efficacy of disinfectants against phenol using specific organisms. While alcohols are another group of disinfectants, they work best in approximately 70% aqueous solutions and are more effective when not impeded by organic matter.