Chi2 value is too high!

Hello. manager

Recently, I am developing a method of Affinity binding between Fc gamma receptor and IgG4.

As you know, the binding is known as weak-binding or no-binding.

So I flowed a high concentration analyte, because I wanted to show that even if there is a high concentration anlyte, both do not bind.
But a sensogram and Rmax of the result was pretty ideal.
The problem is a Chi2. It’s was too high and almost same with Rmax.

I think that a problem is from the analyte concentration. Therefore I will flow the lower concentration analyte.

If you have another advice, please let me know

Thank you

Hello,
Your question is not clear to me. You used a high analyte concentration over the ligand and recorded a nice sensorgram. I conclude that there was binding. You performed a fit and the Chi2 is high. Without seeing any sensorgram and fitting, my conclusion is that the fit is not following your curves.
Please post a sensorgram.
Kind regards
Arnoud

I am sorry about my deficient explaination.
There is the result.

Hi,
I have used your sensorgram to simulate some curves. Top left sensorgram in the figure is based on the overlay I made over your data. The equilibrium plot shows that with only four points you have almost a straight line. It is highly unlikely that you get an accurate equilibrium dissociation constant from these four points. At the bottom I added three lower analyte concentrations. Now the points form the start of an S-shaped curve and the result will be more accurate.


Now for the high Chi2. Because of the relative high response and that the equilibrium points are probably not exactly on the fitted line the residuals and therefore the chi2 is high. If you divide the response values by 10 you will see that the Chi2 wil be lower. I would say two things, lower the ligand concentration to lower the response and use more (lower) analyte concentrations to make a better equilibrium plot.

In addition check www.sprpages.nl/sensorgram-tutorial/a-curve

Kind regards
Arnoud