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A selective and simple method was developed for the determination of four ethyleneamines (EAs), i.e., ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA), by reversed-phase ion-pair chromatography with ultraviolet detection. The method is based on the on-line complexation of EAs with a Cu(II) ion added to the mobile phase. The Cu(II) complexes with EAs (Cu(II)-EA complexes) were well separated on a reversed-phased column, using 1-octanesulfonate as an ion-pairing reagent. The concentrations of 1-octanesulfonate and acetonitrile in the mobile phase significantly influenced the retention times of EAs. The high concentration of the Cu(II) ion in the mobile phase resulted in the increase of the baseline noise. A mixture of acetonitrile and 50 mM acetate buffer at pH 5.5 (23:77, v/v) which contains 0.5 mM CuSO 4 and 20 mM 1-octanesulfonic acid sodium salt was used as the mobile phase. Cu(II)-EA complexes could be detected at 243 nm. The limits of quantification of EAs (S/N = 10) were 0.003 mM for EDA, DETA, and TETA and 0.01 mM for TEPA. The calibration curves were linear over three orders of magnitude of EA concentrations with high correlation coefficients ( r 2 = 1.000). The proposed method was successfully applied to determine EAs in epoxy resin curing agents.