Used primarily as an internal standard in mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the accurate quantification of amoxicillin in biological samples such as plasma, serum, and urine. Its deuterated structure allows it to closely mimic the behavior of non-labeled amoxicillin during sample processing and analysis, ensuring high precision and reliability in pharmacokinetic studies, therapeutic drug monitoring, and metabolism research. Due to its isotopic distinction, it enables clear differentiation from endogenous compounds and the parent drug, reducing analytical interference and improving assay sensitivity.