Complexation equilibria between Cu(II) and new bidentate and tridentate Schiff bases derived from the condensation of 3-hydrazino-6-methyl-[l,2,4]triazine-5(4H)one and aromatic aldehyde derivatives have been studied by zero-order absorption spectrophotometry in ethanol-water solution (50% v/v) at I= 0.1 M (NaClO4) and 25°C. The composition, equilibrium constants of the complexation reactions and overall formation constants of the resultant complexes have been determined and species of the complexes have been clarified. The values of the formation constants are correlated with the sum of the ionization constants of the ligands. A new direct spectrophotometric method for the determination of trace amounts of copper is proposed based on the reaction between Cu(II) and Schiff base derived from p-N,N-dimethyl amino benzaldehyde (HDBe) at pH 6.0. The absorption maximum, molar absorptivity, and calibration sensitivity of 1:2 [Cu(DBe)2] complex are 392 nm, 2.88xl04 L mol-1 cm-1and 0.36 ml μg-1 respectively. The use of second-derivative spectrophotometry eliminates the interference of iron and enables the quantitative determination of Cu(II) in the range 0.15-1.0 ppm with a relative standard deviation of 0.5%. The proposed method has been successfully applied determination of copper in various synthetic samples and in fresh water samples with average percentage recoveries of 99.675±0.045 and 98.95±0.002 respectively