Used primarily as a reference standard in pharmaceutical quality control testing to identify and quantify impurities during the manufacturing and analysis of atomoxetine hydrochloride, a medication for attention deficit hyperactivity disorder (ADHD). It ensures the purity and safety of the final drug product by helping to monitor degradation products and synthetic by-products. Commonly employed in analytical methods such as high-performance liquid chromatography (HPLC) and mass spectrometry (MS) for accurate detection and validation.