Elution behavior of drugs in high-speed counter-current chromatography using on-column complexation with metal ions.

In this study, determination of (nitrogen containing) drugs by on-column complexation with metal ions in high-speed counter-current chromatography (HSCCC) was investigated. Bromazepam (BMP) was strongly retained in the organic upper stationary phase (UP) of the two-phase solvent system composed of tert-butyl methyl ether-acetonitrile-water (2:2:3, v/v/v) by eluting the aqueous lower mobile phase (LP) at a flow rate of 2 mL min. On the other hand, BMP (200 µg mL) was eluted faster without retention to the organic UP with the two-phase system containing 100 μg mL of copper ions (CuCl) because a very polar BMP-Cu complex was immediately formed in the aqueous LP. The dramatic change in the retention behavior of BMP resulted from on-column complexation. The on-column complexation in HSCCC was further investigated for five (nitrogen containing) drugs and seven metal ions. In the result, tizanidine and phentolamine formed complexes with Al, Fe, Co, Ni, Cu, and Zn, ambroxol formed complexes with Al, Fe, and Cu, but voriconazole formed no complexes with all metal ions tested.