A system for in-situ spectroscopic measurements in heterogeneous catalytic reactors includes a reactor having a reactor chamber, a device for collecting a sample, and a device for collecting spectroscopic information. The device for collecting the sample includes a sampling capillary having an orifice situated inside the reactor chamber. The device for collecting spectroscopic information includes at least one optical radiation guide for guiding optical radiation onto the sample for excitation and for collecting optical radiation emitted, absorbed, reflected or scattered by the sample. The at least one optical radiation guide may be inserted into the sampling capillary, such that a tip of the at least one optical radiation guide is proximate to the orifice. A method for analyzing a reactor state including the steps of providing a reactor; collecting spectroscopic information from a sample inside the reactor chamber; and analyzing the collected spectroscopic information is also provided.