A density functional approach to describe adsorption of Lennard-Jones fluids on a surface modified with grafted chains is proposed. The theory is extended to the solute retention in chromatography with chemically bonded phases. The chain molecules are modeled as freely jointed tangent spheres with end segments linked to the surface. The segments interact via Lennard-Jones potential. The effects of grafting density and molecular interactions are discussed. The results are compared with the Monte Carlo simulation data. The theory predicts the most important features of the retention process.