relative SEC and hydrodynamic volume

Question

Hi, 
 
 I have been analyzing some polymers with a more polar solvent on SEC - ELSD detection. (relative to Polystyrene) 
 
 Where I normally measure a MW of 30K for PLA (relative to Polystyrene) in chloroform, I now measure a MW of 140K. 
 In other words, in this polar solvent, the PLA has a bigger hydrodynamic volume, right? 
 
 If the solvent surrounds the polymer more, and this causes a bigger hydrodynamic volume, would the analysis then be incorrect?

Let me know what you think, 
 Roy

andy_coffey · Answer

Hi Roy, 
 Glad to be of some assistance. 
 It seems like the polystyrene standards are eluting later than expected, so it is likely they are interacting with the stationary phase when using the polar solvent. 
 If you have a viscometer then you can certainly gain more insights into the behavior of the polymer in the solvent, but it also helps in situations like yours where the standards you are using are somewhat different to the sample you are analyzing. 
 If you haven't already read this, I recommend you take a look at this primer on multi-detector GPC: 5990-7196EN-BJM.indd (agilent.com) 
 Good luck ! 
 Andy

relative SEC and hydrodynamic volume

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