Stearoyl-L-carnitine-d3 chloride is primarily used in research and analytical studies as a labeled compound. Its deuterated form allows it to serve as an internal standard in mass spectrometry, enabling precise quantification of carnitine and its derivatives in biological samples. This is particularly useful in metabolomics and lipid metabolism studies, where accurate measurement of acyl-carnitines is essential for understanding metabolic pathways and disorders. Additionally, it aids in investigating conditions like fatty acid oxidation defects and mitochondrial dysfunction, providing insights into disease mechanisms and potential therapeutic targets.