### How to normalize/process I(0)

Posted:

**2019.10.10 11:23**Hello everyone,

I am working with several SEC-SAXS curves obtained at Petra III during different trips. I want to estimate the molecular weight of my protein using several different methods, including the equation MW = (N

The intensities from different trips differ by a factor of 10, despite the same protein concentration. The result is that I get MW estimates 1000x too high, or 10000x too high, depending on the date of the data collection. I have checked all the units etc and there is no mistake in my calculations. When I let PRIMUS do the calculations, I get values in the correct (and expected) range. It seems that, in addition to protein concentration, my intensities need to be normalized by some parameter that is present in the files. Can anybody tell me which parameter that is?

I am working with several SEC-SAXS curves obtained at Petra III during different trips. I want to estimate the molecular weight of my protein using several different methods, including the equation MW = (N

_{A}*I(0)/c) / Δρ_{M}^{2}, where I(0) is the extrapolated intensity at q=0.The intensities from different trips differ by a factor of 10, despite the same protein concentration. The result is that I get MW estimates 1000x too high, or 10000x too high, depending on the date of the data collection. I have checked all the units etc and there is no mistake in my calculations. When I let PRIMUS do the calculations, I get values in the correct (and expected) range. It seems that, in addition to protein concentration, my intensities need to be normalized by some parameter that is present in the files. Can anybody tell me which parameter that is?