Versatile applicability of reversed-phase SPE alone which enables the concentration, desalting and partial fractionation of complex proteome samples. Coomassie Blue G250-stained analytical SDS-PAGE of reversed-phase SPE fractionated samples equivalent to (a) approximately 50 g of E. coli whole cell lysate, (b) 1 mL of human urine, also unfractionated (1), and (c) 0.01 mL of rat plasma.