Used as a stable isotope-labeled internal standard in mass spectrometry and HPLC analyses for the accurate quantification of salicylic acid in biological samples such as plasma, urine, and serum. Its deuterated structure allows clear differentiation from non-labeled salicylic acid, minimizing interference from matrix components. Commonly applied in pharmacokinetic studies, toxicology screenings, and metabolic research where precise measurement of drug levels and metabolites is required. Also utilized in dermatological research to trace metabolic pathways and assess dermal absorption rates without altering the biological behavior of the parent compound.