Reversible molecular weight range

Except for the high molecular weight range, nearly all substances can be separated by reversed-phase (RP) HPLC. The many different separation mechanisms in RP HPLC, based on hydi ophobic, hydi ophilic and ion-pairing interactions, and size exclusion effects together with the availability of a lai ge number of high quality stationary phases, explain its great populai ity. At present approximately 90% of all HPLC separations are carried out by reversed-phase mode of HPLC, and an estimated 800 different stationai y phases for RP HPLC are manufactured worldwide. 

As with reverse osmosis, ultrafiltration (UF) and microfiltration (MF) are pressure-driven membrane separation processes, with the membrane permselective for the solvent, usually water. MF and UF separate mainly by size exclusion of the solutes. MF retains particles of micrometer size UF retains particles of submicrometer size by ultramicroporous membranes. Typically, UF retains solutes in the 300 to 500,000 molecular weight range including biomolecules, polymers, sugars, and colloidal particles. 

Heam et al. (75a,b) have reported band width data for the reversed-phase " gradient elution of six peptides with molecular weights ranging from 573 tto 3263. Six different Cn columns were used, with pore diameters of 7-30 nm. Gradient conditions were varied so that 0.1 < 6 < 1, and experitnen- 1a values of a were determined for each run. Thus a rather extensive data >ase was reported. 

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