In the field of superheavy element chemistry, the study of the chemical properties of nihonium (Nh, Z = 113) is currently in the focus. To chemically characterize Nh, fast gas-phase chemistry experiments are essential. Hereto, a new thermochromatographic detection system named LEGEND has been developed for chemistry experiments behind the gas-filled recoil separators SHANS/SHANS2. The presented system will be further developed to higher starting point temperatures of the negative temperature gradient, thereby enabling the investigation of less volatile chemical species. A recoil transfer chamber with a vacuum window acts as an interface between the separator and the thermochromatography detector array, whereas a gas circulation and purification system ensures the required high gas purities. Finally, a state-of-the-art data acquisition system allows for event-by-event α-particle and spontaneous fission fragment spectroscopy. The measurement efficiency of detecting α-particles adsorbed on the active surface is 89.1%. Using the nuclear fusion-evaporation reactions ¹⁶⁹Tm(⁴⁰Ar,xn)^204-206Fr and ¹⁵³Eu(⁴⁰Ar,xn)^184-185Tl, short-lived radioisotopes ²⁰⁵Fr (t_1/2 = 3.92 s) and ¹⁸⁵Tl (t_1/2 = 1.93 s) were produced for first online experiments behind SHANS. The herein presented results render the LEGEND system suitable for gas adsorption chromatography experiments with short-lived ²⁸⁴Nh (t_1/2 ≈ 0.77 s).