Inverted Curve During pH Scouting

I'm completely new to using SPR and have a question about pH scouting. I'm using BI-4000 SPR machine with the CM dextran chip. I've tried various buffers with various pHs however all of them have resulted in a negative/inverted response during pH scouting. The pI of my protein of interest is around 8.0. I've tried looking into the reasons and possible solutions but can't really find much relating to pH scouting.

Any suggestions or advice would be greatly appreciated! 

HI and welcome,

Please can you give the composition of the flow buffer and the buffers used for pH scouting?
And can you post a sensorgram so we can see what is going on.

kind regards
Arnoud