If you have precipitated the protein, then you can use a centrifuge to pellet the protein and resuspend the pellet in whatever volume you need to achieve the desired concentration. You do not need to use a membrane concentrator. However, the protein may not dissolve in aqueous buffer after being precipitated with ethanol because it may be denatured. If this is the case, you may have to dissolve it in a chaotrope such as urea, or in an ionic detergent such as SDS.  You can do gel filtration and ion exchange chromatography with urea-denatured protein solutions, but once you have purified the protein you will have to refold it.

 @ Adam B Shapiro 

Thank you so much for  providing the details regarding my problem

1.The protein precipitated with ethanol did not dissolve completely in sodium phosphate  buffer but it did dissolve completely in tris buffer ph 8. so i continued with it and the protein concentration is 14.88 mg/ml...

which is calculated as:

Net OD for sample =(Subtract BLANK OD from od of sample)=0.155

Then, multiply this net OD with dilution factor=0.155*20=3.1

Then, calculate the protein concentration using standard curve

From standard curve 1 od is 4.8 mg/ml

so 3.1 od will be 4.8*3.1=14.88 mg/ml.

now my question is that is this concentration of protein good enough to do gel filtration or ion exchange chromatography in a column of 50*1.5 cm column with  2ml of this protein sample?

2. Do i need to concentrate it further for chromatography purpose?

2. Do i still need  to dissolve it in urea, or in  SDS?

Hi Himanshu, You have plenty of protein, about 30 mg, at a high enough concentration and in a small enough volume, for gel filtration chromatography. The protein does not have to be at a high concentration for ion exchange chromatography since it will become bound to the column. Since the protein is soluble in water, there is no need to dissolve it in urea or SDS.

A factor of 2-3 for NMWCO filters is usually sufficient to concentrate a soluble protein, so a 30kDa NMWCO spin filter should work. If its an aggregate or multimer a larger filter might work faster but 30kDa or lower is a good place to start.  

For gel filtration do an analytical run (less than 1 mg) to see how your protein behaves with and without urea. Use MW standards to calibrate the column. If your protein is aggregated you may want to use urea (up to 8M, but try 4M and 6M first). If the aggregate is in the void volume and the impurities lag behind, it may be advantageous, though, to omit the urea. If you do use urea, make sure it is ultrapure and don't heat the protein above room temp, or so, to avoid transcarbamylation of the protein in the presence of urea. Note also that you can't do this kind of chromatography in the cold room... the urea will crystallize out.

I am  using 50KD cutoff centricon to concentrating albumin which is 66.40 KD.

Also check if centricon is perfectly working and you are not loosing that in filtrate. 

Also you don't need to concentrate or add into urea or SDS before doing ion exchange chromatography. Moreover,  I think, when you inject or load sample in dilute conditions ( e.g. in AKTA) it will get better adsorbed.