Multistage characterization of label-derived oleamide: chromatographic purification with NMR structural elucidation and UPLC/Q-TOF-MS quantitation for pharmaceutical packaging compatibility assessment

Pharmaceutical labeling is widely used for drug information identification, though compatibility risks persist despite no direct drug contact. This migration risk arises from the semi-permeable nature of primary packaging materials, allowing label additives to permeate into drug formulations. A substantial number of emerging additives, either novel therapeutic agents or structural mimics of prohibited substances, hinder unambiguous liquid chromatography mass spectrometry (LC-MS) identification. To address this, a novel approach is suggested, involving chromatographic separation paired with nuclear magnetic resonance (NMR) spectroscopy for unknown compound identification. High performance liquid chromatography (HPLC) was used to screen the suspected chromatographic peaks and purify them, and then the purified fractions were structurally characterized by ultra-performance liquid chromatography-quadrupole time-of-flight mass (UPLC/Q-TOF-MS) and NMR. Finally, the extractable was identified as oleamide. To quantify oleamide in pharmaceutical labels, a mass spectrometry method with high sensitivity and high resolution was developed and validated using UPLC/Q-TOF-MS. The quantitative approach showed excellent linearity between roughly 0.15 and 2.05 μg mL^-1, with limit of detection (LOD) and limit of quantification (LOQ) values of 50.72 and 153.83 ng mL^-1 (<i>R</i>² = 0.9994). The repeatability, precision, accuracy and robustness were verified to be acceptable. The safety assessment determined that the maximum daily exposure to oleamide in the label of the eye drops tested is 0.015 μg, which is well below the permitted daily exposure (PDE) limit of oleamide. These data demonstrate negligible toxicological risks and confirm the good compatibility between the labels and the ophthalmic formulation.