Lastly I am seeing a lot of unspecific signals like interactions that I did not hope "a priori". Some of these occurs with streptavidin immobilized over the chip.
Is this a normal behaviour?
Usually NaCl buffer concentration is 150 mM and 0.005%Tween20.
Also, only comercial buffer injections show that the signal increases as the injection proceeds.
Sometimes a higer salt concentration can be of help but binding is often salt concentration depend. Thus you should check!
I see often drift after changing buffer type or cleaning the machine. This can last for one or two days. Thorough washing of the system is essential. Flowing overnight at 20 ul.min with some injections of the same buffer should stabilize the system.
And last. Calculate your drift back to the machine specifications. Often people want less drift than the machine can deliver.