The invention relates to a method for determining the free chlorine concentration in a first liquid solution (11), comprising the following steps: a first step (101) of introducing the first liquid solution (11) into an analyser (12) comprising a redox probe (16)； a second step (102) of measuring the pH of the first liquid solution (11)； a third step (103) of adding sodium hydroxide until a second liquid solution (15) with a pH higher than 12, preferably between 12.5 and 12.8, is produced, the third step (103) being preferably carried out at the same time as the second step (102)； a fourth step (104) of determining a value of the redox potential of the second liquid solution (15) by the redox probe (16)； and a fifth step (105) of determining the free chlorine concentration in the first liquid solution (11) according to the value of the determined redox potential. The invention also relates to a device for determining the free chlorine concentration of a first liquid solution.
