Hello,

I'm wondering about the best method to measure the protein concentration in protein samples (Tissue samples and cell culture samples) extracted with Ripa buffer (Sigma-Aldrich, R0278).

We have tried using the NanoDrop (ND-1000) and the Protein Quantification Kit - Rapid from Sigma (based on Coomassie blue, Sigma-Aldrich, 51254). The NanoDrop seemingly can't cope well with the viscose solution, so one and the same sample can have quite good or any concentration, including negative values, if measured several times in sequence. The Sigma kit unfortunately reacts with the Ripa buffer itself, giving us a standard curve with a too shallow slope to calculate correct protein contents.

Does anyone have a good suggestion of which alternative quantification method to use together with Ripa buffer?

Alternatively, I can extract protein from small samples with the Qiagen AllPrep kit (Qiagen, 80284). Which buffer would you suggest to dissolve the protein pellet in afterwards? (However, I need to preserve the sample for future testing as well, e.g. freeze it.)  

Thanks a lot!

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