A new liquid chromatography method has been developed and validated for the analysis of LI-S ((5R)-N-{[3-(3-fluoro-4 -morpholinylphenyl) -2-oxo-5-oxazolidynyl] methyl}acetamide)  (Fig.1) and its impurities L7 ((5R)-[3-(3-fluoro-4 -morpholinylphenyl) -2-oxo-5-oxazolidynyl] methanol) and L9 ((5R)-[3-(3-fluoro-4-morpholinylphenyl) -2-oxo-5-oxazolidynyl] metyl azide).

Fig. 1 Molecular structure of LI-S

The separation was achieved on a C18 column with a mobile phase consisted potassium phosphate dibasic buffer, and acetonitrile. In the course of research its was found that the separation between LI-S and L7 is a critical parameter, and its value should be higher than 1.5.

Validation of the method included: selectivity, specificity, method precision, intermediate precision, accuracy (recovery), linearity, limits of detection and quantitation (LOD and LOQ), robustness. The selectivity of the method for chemical impurities determination was demonstrated for 3 analytes: LI-S, L7 (RRT 0.9) and L9 (RRT 2.9). 
The method for chemical impurities determination was found to be linear (with an R² value of 0.999) and precise (with and RSD value of 1.4 %). The LOQ and LOD for LI-S and its chemical impurities were calculated and were found to be 0.01 % and 0.007 % respectively.

The developed and validated method meets the EP criteria of acceptance.

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