Figure 2: The chromatograms of colistin sulphate and colistimethate sodium (CMS). The liner gradient was: 20% B (acetonitrile) + 80% A (0.05% TFA aqueous solution) changed to 50% B+50% A in 10 min. 5 ÁL of the samples were injected into the HPLC system, respectively. The UV detector was set as 214 nm. (a) The chromatograms of colistin sulphate; (b) The chromatograms of CMS).