Quinaprilat-d5 is primarily used in research and analytical applications as an internal standard in mass spectrometry. It aids in the accurate quantification of quinaprilat, the active metabolite of quinapril, in biological samples such as blood or plasma. This deuterated compound is essential for ensuring precision in pharmacokinetic studies, helping researchers understand drug metabolism and distribution in the body. Its use is critical in developing and validating analytical methods for therapeutic drug monitoring and ensuring compliance with regulatory standards in pharmaceutical research.