Dear Mohamed

You can stor the serum samples in -80 C for long time but if your samples are fresh, the proteomic results will be better.

It is better to aliquot your serum samples in different tubes and in each step use one of them to prevent freeze and thaw stress.

You may add a small amount of protease inhibitor coctail if you are not going to use it immediately.

Which protein will you be working on? Check it's stability and how freeze thaw affects it, You can store proteins as aliquots in -80 but with good cryoprotectants for a long time.

Thank you for your valuable comments.