Used as a stable isotope-labeled internal standard in mass spectrometry-based bioanalytical assays for the quantification of desipramine in biological matrices such as plasma, serum, or urine. Its primary application is in pharmacokinetic and metabolism studies, where it helps ensure accurate and reliable measurement of desipramine levels by compensating for matrix effects and instrument variability. Commonly employed in clinical research and therapeutic drug monitoring to support the development and validation of analytical methods.