The lifeguard of a swimming pool must regularly measure the chlorine content. It measures the parameters "total chlorine", "combined chlorine" and "free chlorine".
When adding a chlorine-containing agent to the pool water, some of the chlorine is decomposed and bound by impurities. Hair, dander, urine and other dirt bind chlorine, which is then no longer available for disinfection, i.e. for killing microorganisms. This is the "combined chlorine". In order to determine the amount of chlorine that is still available for disinfection, a lifeguard also measures the "free chlorine" parameter. The sum of "combined chlorine" and "free chlorine" then results in "total chlorine".
The content of "free chlorine" which, as mentioned above, is "freely" available for killing microorganisms is important for the disinfection performance and thus protection of the bathers from infections. In the English-speaking world, the term "free chlorine" is not used in the form of "free chlorine", but the term "active chlorine", i.e. active chlorine; actively ready to kill. As part of the European approval process for active ingredients in accordance with the biocide regulation and the associated use of the English language, the term "active chlorine" was used to describe the disinfecting chlorine content of the active ingredients sodium hypochlorite, hypochlorous acid, chlorine produced electrolytically from common salt and other chlorine-containing substances Classify products.
The translation back into German was then done verbatim with the term "active chlorine" and not as it was originally called and would be appropriate in German, as "free chlorine". In German-speaking countries, for example, the term “active chlorine” has become established and is used in general. An Anglicism.
Hypochlorite enters the cell either by using an existing channel or by being pumped into the cell by the cell's own transport mechanisms. Water plays the central role here. The actually effective chlorite ion previously had to “hang” on HO so that it becomes hydrophilic (attractive to water) and can cross the cell wall. OCl, on the other hand, is hydrophobic (water-repellent), so cannot hope for water as a means of transport, stays outside and is therefore ineffective.