Benzyl Fentanyl-d3 is a deuterated isotopically labeled analog of benzyl fentanyl, a synthetic opioid. It serves as an internal standard in analytical chemistry, particularly for LC-MS/MS quantification of fentanyl and its analogs in forensic, pharmaceutical, and toxicological applications. This specialty chemical features high deuterium enrichment (≥98 atom % D) for precise mass spectrometry analysis.