A simple method for assaying colistimethate sodium in pharmaceutical aerosol samples using high performance liquid chromatography

A rapid and simple reversed-phase high performance liquid chromatography (HPLC) method for the quantitation of colistimethate sodium in pharmaceutical formulations has been developed. The chromatographic separation was performed using a Phenomenex Kinetex XB-C18 column with gradient elution using a mobile phase containing acetonitrile and 32mM sodium sulphate. Quantitation is based on the sum of the areas of two prominent peaks in the chromatogram, which produces a total peak area that is stable for 120 sample injections. The HPLC method was validated over the range 0.05-7mg/mL, and was shown to be suitable for the analysis of aerosolised pharmaceuticals in terms of aerosol output onto filter and for the analysis of samples from a cascade impactor, which is used for the determination of aerosol particle size.