The invention pertains to a system for operando measurements that comprises, a reactor (1) comprising a reactor chamber (9) having at least one window (19) transparent for radiation for irradiating a sample (24) provided inside the reaction chamber (9), a radiation source (21, 31) for generating the radiation for irradiating the sample (24), wherein the radiation source (21, 31) is arranged to irradiate the sample at an irradiation location situated on the sample; a detection unit (26, 33) for detecting radiation scattered, emitted, reflected or diffracted by the sample (24) or transmitted through said sample (24), a sampling capillary (12) comprising an orifice (14) for collecting a fluid sample inside the reactor chamber (9), wherein the orifice (14) of the sampling capillary (12) is arranged at a fixed position relative to the irradiation location, wherein the reactor (1) is movable relative to the radiation source (21, 31).