when should we set RI=0 for a 1:1 fit?

See, i do understand that RI is for bulk shift accommodation when the running buffer and sample buffers are mismatched. but my question is when I chose a 1:1 model of curved fitting what criteria do i also look into to set RI=0 ? or i use the default setting. ? My sample buffer and running buffer is the same...

In general the RI is fitted along with the other parameters. Fitted RI should be low and proprtional to the analyte concentration.
I my opinion the RI is often calculated too large.
I always start with RI=0 to determine the Rmax, ka and kd. Then I add RI-fitting and start the fitting with the values of the previous fitting.

Look at the second figure at www.sprpages.nl/sensorgram-tutorial/curve-fitting.html .
Make sure you don't have this.

hey arnoud,

I do have large RI jumps after setting RI=0 and not as large when I have RI as a fitted parameter...

Any inputs?

Lets clear something up.
If I use RI=0 I mean that I keep RI as a constant on zero. Thus assuming there is no RI effect. Ergo there can be no RI value other than zero.
If you set RI=0 and the fit it locally (must be local!) then the progam wil fit a value starting with zero. The default fittings use often a starting value of 10 or 50. When fitting clean sensorgram the answers should be comparable regardless the starting value (unless really extreme).

So I normally start fitting without RI --> RI=0 and a constant, Then after I have the ka, kd and Rmax, I fill in these values and set RI=0 and fit locally.
Maybe you can show the two fittings with values (or otherwise send a message via the contact form).

there is some undercurrent of confusion that I have... can i talk to you?. any which way i will post the sensogram ... I use Biaevaluation software t100/200..

here i paste two sensograms... one with RI=0 and one with RI= fitted..
I have fcgRIIIa immobilised at 250 RU
there are 8 conc. of the drug product
Query is, I see when I use RI=0 the fitting is bad in 1:1 model and when I use RI= fitted i see a better fit... but i don't know if i could use RI=fitted or when I should use RI= 0...