i want toknow that is the retention time of the compound depends on the concentration of the compund and why ,

I hope that this is not the question on Monday's quiz. But I will give it to you anyway since you were up so late working on chemistry.

Because of the finite capacity of a column, there will be differences in retention time according to concentration. The equilibrium constant for the drug between the mobile phase and stationary phase is a physical constant. Once the stationary phase has been saturated that portion of the stationary phase is no longer available to the individual molecule and that molecule is swept by to an open portion of the column. The net effect is that at larger concentrations the peak width is wider and the retention time is shorter. I hope this simplified explanation helped you to understand the chemistry of chromatography.