I want to use 5mM Hepes because the research had study the interaction by another techniques and she would like to reproduce the same buffer conditions. I think she use Hepes alone. It isn't 150 mM in NaCl. But for her it is also important to have a good pH reproducibility. The interaction should be study a pH 7.4 and pH 8.5. The analyte change its conformation between this 2 pH. I think above pH 8.
If a 5mM Hepes concentration it isn´t advisable, please tell me and I´ll use Hepes 10mM?
Can you gave me your Hepes recipe to check mine?
I use in general 10 mM Hepes pH 7.4, 150 mM NaCl + 0.005% P20.
The Hepes as a buffer component, the NaCl to make the buffer more fysiological and to diminisch some non-specific initeraction and the P20 (tween-20) also to reduce non-specific binding. Sometimes I add calcium or EDTA depending on the application
That said, there are a lot more other buffer systems around wich perform equally well. You must use the buffer which is suitable for your application.
I gues you want to have a stable protein at pH 7.4, so use the 10 mM Hepes and adjust the pH to 7.4.
To observe conformational change per se, I would not recommend SPR. Use Circular Diochrism instead.