Correcting Contrast for SAXS data?

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wally
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Correcting Contrast for SAXS data?

#1 Post by wally » 2009.03.02 15:17

sorry if these are silly questions, but I've just read a few things that created some questions:

Is it possible to correct SAXS data on samples containing glycerol (ie: 5%) or significant amounts of NaCl (ie: 450mM)? What is the proper ("best practice") way of doing this?

How does one properly predict a priori if, for a given radiation source, the buffer conditions will create contrast problems. Does this vary from source to source?

thanks!

mgajda
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Re: Correcting Contrast for SAXS data?

#2 Post by mgajda » 2009.03.03 16:53

wally wrote:sorry if these are silly questions, but I've just read a few things that created some questions:

Is it possible to correct SAXS data on samples containing glycerol (ie: 5%) or significant amounts of NaCl (ie: 450mM)? What is the proper ("best practice") way of doing this?

How does one properly predict a priori if, for a given radiation source, the buffer conditions will create contrast problems. Does this vary from source to source?

thanks!
Not silly at all .

At least my attempt at answering them is a bit involved:

Best way to correct is to use last dialysis buffer containing these additions in exactly the same amount as the sample (exactness requirement is the reason for use of dialysis.)

You can compare contrast of particulate sample against solution by computing average electron density of the buffer vs electron density of the protein. Contrast should be proportional to squared difference between these. To get average electron density of the buffer, I think, would be a sum of all average electron densities of the components weighted by their volume fractions.

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