A high surface area silica has been modified with 3-(Trimethoxysilyl)-1-propanethiol groups. The silica retains its surface area after the treatment. The characteristics of this modified silica and its application to the preconcentration separation of cobalt and nickel prior to determination by Graphite Furnace Atomic Absorption Spectrometry (GFAAS) are described. Both batch and column methods were studied. The experimental parameters such as the effect of pH of the sample and eluent, flow rate of eluent, the column and the amount of silica on sorption and elution has been investigated.