Spectrophotometric determination of linezolid in pharmaceuticals on the basis of coupled redox-complexation reactions

The present study describes three simple and sensitive spectrophotometric methods developed for the determination of linezolid (LZD) in pure and tablet forms. These methods are based on the oxidation of LZD by ferric chloride in the presence of 1,10-phenanthroline (method A), or 2,2′-bipyridyl (method B), or potassium ferricyanide (method C). The colored complexes were measured at 510, 522 and 758 nm for methods A, B and C, respectively. In all the methods, the absorbance is found to increase linearly with increasing LZD concentration. Beer’s law is obeyed over the concentration ranges of 0.5–6.0, 0.5–9.0 and 1.0–9.0 μg/mL for methods A, B and C, respectively. The calculated molar absorptivity values are 5.8 × 104, 3.6 × 104 and 4.8 × 104 L/mol cm for methods A, B and C, respectively, and the corresponding Sandell’s sensitivities are 5.8 × 10−3, 9.8 × 10−3 and 7 × 10−3 μg/cm2, respectively. The developed methods are applied successfully to the determination of LZD in the pharmaceutical formulations and the results tallied well with label claims.