The continuous development of the pharmaceutical industry has accentuated the task of quality assurance of medicines, which can be solved using standardization and further quality control of medicines. For these purposes, various physicochemical methods can be employed, often using reference standards (RSs) to obtain reliable data during research. Spectral data obtained by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy were comprehensively analyzed during the development of RSs of antihypertensive drugs of the angiotensin-converting enzyme (ACE) inhibitor class, e.g., Captopril and Enalapril, which were identified during the analysis. The obtained data could be used in the pharmaceutical analysis of medicines that contain drug substance Captopril or Enalapril as the active ingredient and will also be included in the regulations for the corresponding RSs. © 2022, Springer Science+Business Media, LLC, part of Springer Nature.