Palmitoyl carnitine-d3 HCl (CAS No.: 1334532-26-1) is a stable isotope-labeled standard of Palmitoyl carnitine, with deuterium labeling mainly located on the N-methyl group. Palmitoyl carnitine is a long-chain acylcarnitine that plays a key role in fatty acid metabolism and mitochondrial energy production. Due to its importance in cellular energy metabolism, Palmitoyl carnitine and its isotope-labeled standards are commonly used in metabolomics studies, especially in liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis, as internal standards to improve the accuracy of quantitative analysis. In cell and animal models, applications of Palmitoyl carnitine typically involve its effects on mitochondrial function, lipid metabolism, and related signaling pathways. The dose or concentration used in experiments usually depends on the experimental design and research objectives. Owing to the stable isotope labeling properties of Palmitoyl carnitine-d3 HCl, it has broad applications in pharmacokinetics, metabolic pathway tracing, and biomarker identification. When using this compound in experiments, the experimental plan should be reasonably designed according to specific experimental needs and objectives to ensure data reliability and reproducibility.