For plasma membrane purification you need a microsomal fraction further purified by aqueous two phase partitioning or sucrose gradient centrifugation. As a bibliographical source maybe the following will help you:
Zhang ZJ, Peck SC.Simplified enrichment of plasma membrane proteins for proteomic analyses in Arabidopsis thaliana. Proteomics. 2011 May;11(9):1780-8
Alexandersson E, Saalbach G, Larsson C, Kjellbom P.Arabidopsis plasma membrane proteomics identifies components of transport, signal transduction and membrane trafficking. Plant Cell Physiol. 2004 Nov;45(11):1543-56
Nühse TS, Stensballe A, Jensen ON, Peck SC.Phosphoproteomics of the Arabidopsis plasma membrane and a new phosphorylation site database. Plant Cell. 2004 Sep;16(9):2394-405
Marmagne A, Rouet MA, Ferro M, Rolland N, Alcon C, Joyard J, Garin J, Barbier-Brygoo H, Ephritikhine G.Identification of new intrinsic proteins in Arabidopsis plasma membrane proteome. Mol Cell Proteomics. 2004 Jul;3(7):675-91