Acetyl Fentanyl-d5 is a deuterated internal standard analog of the synthetic opioid Acetyl Fentanyl. It is used in analytical laboratories for quantitative analysis of fentanyl derivatives via techniques such as LC-MS/MS. This specialty chemical features high isotopic purity, with 98 atom% deuterium incorporation, making it suitable for precise mass spectrometry applications in forensic, pharmaceutical, and research settings.