is generally one which comprises a glass, silica, agarose or polystyrene surface. The solid phase may be a purification colunm or a discontinuous phase of discrete particles. In preferred embodiments, the solid phase is a controlled pore glass colunm or a silicic acid colunm. In certain embodi- ments, the solid phase is coated with a reagent (such as glycerol), which is intended to prevent nonspecific adher› ence of contaminants to the solid phase. 

A "buffer" is a buffered solution that resists changes in pH by the action of its acid-base conjugate components. 

An "equilibration buffer" herein is that used to prepare the solid phase for chromatography. 

The "loading buffer" is that which is used to load the mixture of the protein and contaminant(s) onto the chroma› tography matrix. The equilibration and loading buffers can 15 be the same. 

The "elution buffer" is used to elute proteins from the chromatography matrix. 

A "salt" is a compound formed by the interaction of an acid and a base. 

In one embodiment, the organic acid includes, but is not limited to, formic acid, acetic acid, lactic acid, citric acid, malic acid, maleic acid, glycine, phosphoric acid, glycyl› clycine, succ1mc acid, TES (2-{[tris(hydroxymethyl) methyl]amino }ethanesulfonic acid), MOPS (3-(N-mor› pholino )propanesulfonic acid), PIPES (piperazine-N,N’-bis (2-ethanesulfonic acid)), and MES (2-(N-morpholino) ethanesulfonic acid). 

In one embodiment, the organic base includes, but is not limited to, the group consisting of tris base, arginine, Bis› Tris, Bis-Tris-Propane, Bicine (N,N-bis(2-hydroxyethyl) glycine), HEPES ( 4-2-hydroxyethyl-1-piperazineethanesul- fonic acid), TAPS (3-{[tris(hydroxymethyl)methyl] amino }propanesulfonic acid), and Tricine (N-tris (hydroxymethyl)methylglycine ). 

In one embodiment, the conjugate base of the organic acid is the sodium, potassium, or ammonium salt of the conjugate base of the organic acid. In one embodiment, the organic acid is acetic acid and the conjugate base of acetic acid is the sodium salt. 

In one embodiment, the protein is an antigen binding protein. In one embodiment, the antigen binding protein is an antibody. In one embodiment the antibody is of the IgG class. In one embodiment, the antigen binding protein is a immunoglobulin single variable domain. 

In one embodiment, the sequence of chromatographic steps comprises protein A chromatography and flowthrough anion exchange chromatography. In one embodiment, the sequence of chromatographic steps comprises protein A chromatography, flowthrough anion exchange chromatogra- phy, and cation exchange chromatography. 

In one embodiment, the sequence of chromatographic steps comprises protein A chromatography performed in the presence of about 55 mM tris base, about 45 mM acetic acid, at about pH 7.5. 

In one embodiment, the sequence of chromatographic steps comprises flowthrough anion exchange chromatogra› phy performed in the presence of about 55 mM tris base, about 45 mM acetic acid, at about pH 7.5. 

In one embodiment, the sequence of chromatographic steps comprises cation exchange chromatography performed in the presence of about 25 mM sodium acetate, about 12.1 mM acetic acid, at about pH 5.0. 

In one aspect, the present invention is directed to a method for purifying a protein from a contaminated solution 65 thereof by Protein A chromatography comprising: (a) equili› brating a Protein A immobilized on a solid phase with a 

Protein A equilibration buffer comprising about 55 mM tris base, about 45 mM acetic acid, at about pH 7 .5; (b) adsorbing the protein from the contaminated solution to the Protein A immobilized on the solid phase; (c) removing contaminants by washing the solid phase with a first Protein A wash buffer comprising about 55 mM Tris Base, about 45 mM Acetic acid, 300 mM Sodium Acetate, at about pH 7 .5; and ( d) recovering the protein from the solid phase with a Protein A elution buffer comprising about 1.8 mM Sodium Acetate, about 28.2 mM Acetic acid, at about pH 3.6, wherein all the buffers are made without the addition of NaCl. 

In one embodiment, the method further comprises the following step after step (c) and before step (d): removing contaminants by washing the solid phase with a second Protein A wash buffer comprising about 55 mM Tris Base, about 45 mM Acetic acid, at about pH 7.5, wherein the second Protein A wash buffer is made without the addition of NaCl. 

In one embodiment, the method further comprises the following steps after step ( d): ( e) titrating the solution containing the recovered protein to about pH 3.0 with about 30 mM acetic acid, about 100 mM HCl; (f) allowing the solution of step (e) to remain at about pH 3.0 for about 30 to about 60 minutes; and (g) adjusting the pH of the solution of step (f) to about pH 7.5 with about 1 M Tris. 

In one embodiment, the method further comprises filter› ing the solution produced by step (g) above. 

In one aspect the present invention is directed to a method for purifying a protein from a contaminated solution thereof by flowthrough anion exchange chromatography compris› ing: (a) equilibrating an anion exchange matrix with an anion equilibration buffer comprising about 55 mM tris base, about 45 mM acetic acid, at about pH 7 .5; (b) applying the contaminated solution to the anion exchange matrix and collecting the first flowthrough; and ( c) applying an anion wash buffer comprising 55 mM Tris Base, about 45 mM Acetic acid, about 300 mM Sodium Acetate, at about pH 7 .5 to the anion exchange matrix and collecting the second flowthrough, wherein all the buffers are made without the addition of NaCl. 

In one embodiment, the contaminated solution is the solution produced by step (g) of a method for purifying a protein from a contaminated solution thereof by Protein A chromatography comprising: (a) equilibrating a Protein A immobilized on a solid phase with a Protein A equilibration buffer comprising 55 mM tris base, 45 mM acetic acid, at about pH 7.5; (b) adsorbing the protein from the contami› nated solution to the Protein A immobilized on the solid phase; ( c) removing contaminants by washing the solid phase with a first Protein A wash buffer comprising 55 mM Tris Base, 45 mM Acetic acid, 300 mM Sodium Acetate, at about pH 7.5; and (d) recovering the protein from the solid phase with a Protein A elution buffer comprising 1.8 mM Sodium Acetate, 28.2 mM Acetic acid, at about pH 3.6, wherein all the buffers are made without the addition of NaCl. or the filtered solution of a method of purifying a protein from a contaminated solution thereof by Protein A chromatography comprising: (a) equilibrating a Protein A immobilized on a solid phase with a Protein A equilibration buffer comprising 55 mM tris base, 45 mM acetic acid, at about pH 7.5; (b) adsorbing the protein from the contami› nated solution to the Protein A immobilized on the solid phase; ( c) removing contaminants by washing the solid phase with a first Protein A wash buffer comprising 55 mM Tris Base, 45 mM Acetic acid, 300 mM Sodium Acetate, at about pH 7.5; and (d) recovering the protein from the solid 

