Gas-liquid reactions represent an important and popular reaction type in chemical industry. On this account, the understanding of ongoing mass transport processes is of high importance. Nevertheless, there is still insufficient information on the interaction between mass transfer and chemical reaction, mainly due to the problem of decoupling mass transfer and reaction. To tackle this challenge, the possibility of decoupling these processes is introduced by use of photochemical reactions as switchable reactions. The feasibility of this concept is demonstrated by taking the photochlorination of toluene as an example. Experimental results show that the aimed separation of mass transfer and reaction can be achieved, providing an innovative tool for the investigation of mass transfer processes.