Despite numerous advancements in synthesizing photoactive materials, the evaluation of their catalytic performance remains challenging since their fabrication often involves tedious strategies, yielding only low quantities in the μ-gram scale. In addition, these model catalysts exhibit different forms, such as powders or film(-like) structures grown on various supporting materials. Herein, we present a versatile gas phase μ-photoreactor, compatible with different catalyst morphologies, which is, in contrast to existing systems, re-openable and -useable, allowing not only post-characterization of the photocatalytic material but also enabling catalyst screening studies in short experimental time intervals. Sensitive and time-resolved reaction monitoring at ambient pressure is realized by a lid-integrated capillary, transmitting the entire gas flow from the reactor chamber to a quadrupole mass spectrometer. Due to the microfabrication of the lid from borosilicate as base material, 88% of the geometrical area can be illuminated by a light source, further enhancing sensitivity. Gas dependent flow rates through the capillary were experimentally determined to be 1015-1016 molecules s-1, and in combination with a reactor volume of 10.5 μl, this results in residence times below 40 s. Furthermore, the reactor volume can easily be altered by adjusting the height of the polymeric sealing material. The successful operation of the reactor is demonstrated by selective ethanol oxidation over Pt-loaded TiO2 (P25), which serves to exemplify product analysis from dark-illumination difference spectra.