It's been a long time since I played with seed proteins, but they are separated, usually, by their solubilities. The 7S and 11S of soybean are globulins, and are usually soluble in saline, while albumins, probably your 2S, are water soluble. Prolamins tend to require base, or perhaps organic solvents, but I don't think you are going after those.
See the following:
Peter R. Shewry,' Johnathan A. Napier, and Arthur S. Tatham (1995) The Plant Cell, Vol. 7, 945-956, Seed Storage Proteins: Structures 'and Biosynthesis