Experiments to separate nickel and chromium were carried out at 298 K on a porous glass packed-column using citric acid as an eluent. With increases in citric acid concentration in the eluent and in pH, the retention volume of both metals decreased, and the degree of overlap of the elution curves increased, due to the elution effect of secondary dissociated citric acid ion. With decrease in the particle diameter of the packing material, the elution curve narrowed and the degree of overlap of the elution curves decreased considerably, but the void volume in the column and the retention volume of both metals hardly changed. When porous glass powder of 100-200 mesh was packed in a column of 300 mm in length, nickel and chromium were elated isocratically by 30 cm(3) or less eluent containing 0.025-0.030 mol/dm(3) of citric acid at pH 3.5, and a degree of overlap of 4-6% was obtained. Then, it was shown that the elution time can be remarkably shortened by using citric acid rather than acetic acid as an eluent.