Membrane osmometry measurements are best used for 30,000  1,000,000 grams/mole. For  above 1,000,000 grams/mole, the solute is too dilute to create a measurable osmotic pressure. For  below 30,000 grams per mole, the solute permeates through the membrane and the measurements are inaccurate.
Another issue for membrane osmometer is the limited membrane types. The most common membrane used is cellulose acetate; however, cellulose acetate can only be used with toluene and water. While toluene and water are useful solvent for many compounds, not all polymers are miscible in toluene or water. Regenerated cellulose membranes can be used for many other solvents, but are hard to obtain.