Derivative Spectrophotometric Methods for the Analysis and Stability Studies of Colistin Sulphate

Simple spectrophotometric methods were developed for the quantitative determination of colistin sulphate in bulk and dosage forms. The methods were based on the measurement of first and second derivative spectra of colistin sulphate at 298 nm and 318 nm, respectively. Beer's law was obeyed in the concentration range 800-4000 IU/mL with good correlation coefficient (not less than 0.998) for bothmethods. The developed first derivative spectrophotometric method was then selected to study the degradation behavior of colistin sulphate in alkaline media at different temperatures as the second derivative method failed to give reproducible results for the stability study. The pH-rate profile indicates a first-order dependence of the degradation rate on [OH-] at pH ranging between 8 and 11. The obtained results for the photochemical study reflected photostability of colistin sulphate.