A new, cost-effective and sensitive spectroscopic assay for the quantification of Colistin Sulfate (CS) and its prodrug colistimethate sodium (CMS) has been developed and validated. The validated technique depends on the condensation of the studied drug with 2,2-dihydroxyindan-1,3-dione (ninhydrin) and phenylacetaldehyde using Teorell and Stenhagen buffer (pH = 6) to yield a fluorescent product that is estimated at emission wavelength (λ em = 474 nm) after excitation wavelength (λ ex = 390 nm). The reaction's affecting factors were carefully studied and adjusted accurately. Over the following range (0.4-2.4 μg mL-1), the produced calibration plot looked rectilinear, and the estimated limits of detection and quantification (LOD and LOQ) were 0.051 & 0.154 μg mL-1 respectively. The recommended approach was utilized to evaluate market products containing the investigated drug. Moreover, content uniformity testing was employed as a new procedure not found in the previously reported fluorimetric technique.
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