•A new FIA–DEMS configuration has been developed to characterize screen-printed electrodes (SPEs).•HER on a SPE modified with carbon-supported platinum catalyst was studied.•In-situ spectroelectrochemical identification/quantification of H2 was accomplished.•A vast diversity of electrochemical reactions can be studied by the novel FIA–DEMS. In situ detection and quantification of reaction intermediates and products is of paramount importance in applied and fundamental research. In the present work, differential electrochemical mass spectrometry (DEMS) is coupled with flow injection analysis (FIA) to study the hydrogen evolution reaction (HER) on a carbon screen-printed electrode (SPE) modified with a carbon-supported platinum (Pt/C) catalyst. Using this approach, the gaseous and volatile species produced during an electrochemical reaction of interest can be detected and quantified. The reported results support the viability of the novel setup, which can be employed not only for the HER, but also for a vast diversity of electrochemical reactions occurring at various modified SPEs.