Methods Antioxidant, metal ion chelating agent and the mixture of the two were added to the lotion respectively, and the color of compound salicylic acid lotion was observed.

Complexing agent: can with metal ions or containing metal ions compounds formed the material with complex.

The complexes formed in organic solvent, aqueous and micellar solution are injected into chromatographic system or the metal ions are injected into the eluent containing the chelating agent.