A process for hydrogenating a sample in a pressure range below supercritical pressure values includes supplying at least a solvent of the sample to be hydrogenated by a feed pump with a constant volume rate into a flow path to create a base solution; adding the sample being dissolved into the flow path; feeding hydrogen into the flow path through a valve configured to transmit hydrogen only into a single direction; leading the dissolved sample in the presence of a catalyst through a hydrogenation reactor, where the reactor is inserted into a section of the flow path located after the hydrogen feeding position; maintaining the pressure of the reaction in a given pressure range by element of a pressure-adjusting unit, and collecting a hydrogenate formed within the hydrogenation reactor in a product receptacle connected to the end of the flow path.