The present invention, referred to as Surface-Free Affinity Purification (SFAP), relates to a system and method for purifying low abundance peptides, including digested plasma proteins. SFAP combines the components and processes of Surface-Free Isolation, Specific Competitive Elution, Dual Epitope Isolation and Protective Solvents in the purification of low abundance proteins, all of which may be performed in a single column. This column is a constant volume Diafiltration Column equipped with stirring that can be driven by an HPLC. Digested plasma may be injected into the Diafiltration Column by the HPLC. Immunoglobulins, Specific Competitive Elutants, Protective Solvents are injected in a series of injections that result in the purified peptides bound to the surfaces of a very-low volume hydrophobic reversed phase trap from which they can be easily injected into mass spectrometry detection instruments.
