The performance of six 2-quinolylazo compounds (HL) as precolumn derivatizing reagents for reversed-phase high-performance liquid chromatographic separation of metal ions using an ODS column was studied. Four metal ions were detected as [Fe I I L 2 ], [Co I I I L 2 ] + , [NiL 2 ] and [Cu I I L] + , respectively. Addition of thiocyanate ion to the mobile phase enhanced the retention of [Cu I I L] + to give a better separation from the solvent peak, compared with other anions. Phenol derivatives afforded a shorter analytical time than naphthol derivatives. Replacement of acetonitrile by acetone as organic modifier reduced the retention of Fe, Ni and Co more than that of a free ligand and Cu, and induced the change of elution order from Cu, Co, HL, Ni, Fe to Co, Cu, Ni, Fe, HL.