A selective and sensitive reagent of 2-pyridine carboxaldehyde isonicotinyl hydrazone(2-PYAINH)was synthesized and studied for the spectrophotometric determination of nickel,copper,cobalt,and iron in detail.At a pH value of 7.0,9.0,9.0,and 8.0,respectively,which greatly increased the selectivity;nickel,copper,cobalt, and iron reacted with 2-PYAINH to form a 1:2 yellow-orange,1:2 yellow-green,1:2 yellow and 1:1 yellow complexes,with absorption peaks at 363,352,346,and 359 nm,respectively.Under the optimal conditions,Beers law was obeyed over the ranges of 0.01-1.4,0.01-1.5,0.01-2.7,and 0.01-5.4 mg/L,respectively.The apparent molar absorptivity and Sandells sensitivities were 8.4×104,5.2x104,7.1×104,and 3.9×104L·mol-1.cm-1,respectively,and 0.00069,0.0012,0.00078,and 0.0014 μ g·cm-2,respectively.The detection limits were found to be 0.001,O.002,0.003,and 0.01 mg/L,respectively.The detailed study of various interfering ions to make the method more sensitive was carried out and selective and several real samples were analyzed with satisfactory results.