Quantitative UPLC analysis of linezolid and associated organic impurities in drug substances and products

Linezolid is a widely used antibacterial drug, and the control of its related organic impurities and degradation products is necessary to maintain product quality and stability. This study focused on developing and validating a stability-indicating UPLC method for estimation of linezolid and its related impurities in the drug substance and its finished pharmaceutical product. Separation was performed on a BEH Phenyl Shield column using a gradient elution system. Mobile phase A consisted of buffer and acetonitrile, while mobile phase B contained buffer, methanol, and acetonitrile. The flow rate was 0.15 mL/min, with the temperature set at 35°C. Detection was carried out using a photodiode array detector at 210 and 254 nm, and the method was validated according guidelines of ICH. The proposed method provided efficient separation of linezolid, its related impurities, and degradants. A linear response was obtained within the concentration range of 125–750 µg/mL for linezolid and 0.5–5.0 µg/mL for its related impurities. Forced degradation experiments showed that the method was capable of indicating stability. The validated UPLC method was found to be selective, dependable, and appropriate for routine assay, impurity profiling, and stability evaluation of linezolid in drug substances and finished pharmaceutical formulations.