Activated Carbons (AC) are widely used in the ventilation lines of nuclear facilities for the removal of volatile iodine species. In this paper, new experimental methodologies have been developed in order to measure the BreakThrough Curves (BTC) of both radioactive and stable CH3I for KI- or TEDA- impregnated AC {T = 20 – 30 ◦C, dry conditions}. Non-impregnated and KI-impregnated AC were shown to display similar performances for the trapping of stable CH3127I. In that case, only physical interactions within the micropores were involved in the adsorption process. A significant improvement of the retention occurred after TEDA impregnation. Regarding the trapping of the γ-labelled CH3I, a significant enhancement of AC performances during both retention and breakthrough phases is observed after KI impregnation due to the promotion of isotopic exchange phenomenon. Therefore, the contribution of KI, still rarely studied in the literature, was isolated for the first time from the other mechanisms (physisorption and chemisorption). The in-depth analysis of BTC data obtained under active and inactive conditions allowed quantifying the contribution due to isotopic exchange.