You can use the calculator in the Zetasizer to predict the MW from a size (and vice versa).  See:

http://www.materials-talks.com/blog/2014/09/16/faq-molecular-weight-estimate-from-dls/

Extracted values depend on the shape and your 400000 seems in line.  See attached.

700 nm is a large particle - did you have sedimentation as well? 'Precipitate' indicates sedimentation and thus sizes typically in the > 1 um area. 

Thank you sir for your answer. Yes I did use zetasizer instrument itself for the size calculation. However, the results obtained from zetasizer Ml wt calculator are obtained in Kilo daltons, which is obviously not correct. Hence I cannot report the values in obatined in the zetasizer calculator. Can you help me sort out this problem of Kilo daltons?

Also, I think I had sedimentation as well, but for size calculation, I used 1uM filter to avoid any big particles going in. So, i think that way I have eliminated the chances of particles bigger than 1uM for size measurements.

If, as in your question, 'I got Mn to be very high around 400000 dalton' then the intensity MW is going to be substantially greater   Normally one does not quote MW for such large entities.

Thank you sir. But still the units are in Kilo dalton in the calculator. Can you tell me why is it in Kilo dalton?

Hello Sai,

Have you considered utilizing a technique based on melt rheology?

 It would allow you to avoid dissolving your sample.

Regards

Hi sir, no i dont have access to melt rheology instrumentation. But thank you so muh for your useful suggestion, I will if i can do such studies.