If I understand you right, you ask if you should use as a blank the mixture of Bradford reagent with the buffer used to dissolve your protein. My answer is yes. If , for example, I estimate a protein dissolved in PBS, I make a blank of Bradford reagent mixed with PBS in the same proportion like in protein estimation. In your case it is even more important because RIPA buffer contains Tris, deoxycholate etc. , which may input to the absorbance in Bradford reaction, and this input should be accounted for.  

Hello Dr Ivanov,

         Yes, you are right, I was having little doubt but now I am clear on this. thank you for your suggestion,  

Thank you so much for your suggestion,  

Use the RIPA buffer in the blank and standards, at precisely the same amount as in the samples. Various substances can interfere with the Bradford assay, notably the detergents found in RIPA buffer. You would probably be better off using a different protein assay, such as BCA or Lowry, which is not as sensitive to detergents.

Hello Dr Shapiro,

           Thank you so much for your suggestion. I will follow as per your suggestion. 

                Thank you,

Hi there,

By definition, the blank sample corresponds to a mixture containing everything but the essential reagent you want to characterize.