Why albumin provides maximum contribution in the generation of oncotic pressure?

The colloid osmotic pressure due to plasma colloids is called the oncotic pressure. It is determined by the number of molecules dissolved in a fluid rather than by the mass of these molecules. Albumin contributes the maximum to oncotic pressure compared to other proteins like globulins and fibrinogen because it has low molecular weight & high concentration. The colloid osmotic pressure of normal human plasma averages about 28mm Hg. 19mm Hg of this is caused by molecular effects of the dissolved protein and 9mm Hg by the cations held in plasma by the proteins, which is called the Donnan effect. Ref: Cellular Proteins and Their Fatty Acids in Health and Disease, Edited By Asim K. Duttaroy, Page 79.