why linear and single porosity columns can not be combined?

[madalinus]

Hello all!

I would like to separate some degraded polymer samples using SEC, by connecting a linear column to a single porosity column. I would like to do this because I think my samples contain a high MW fraction and a mixture of smaller MW fractions. I think that by using only the linear column, I'd be able to separate the high MW fraction from the smaller ones, but then the smaller fractions won't be properly separated. To me it seemed that a solution would be to add a single porosity column that we bought especially for the smaller fractions. I read here that you can not combine the linear with the single porosity columns: http://pssgpcshop.com/columns3.htm . Why is this?

Thank you,
Madalina.

[tom jupille]

You *can* combine the columns, but if you are trying to characterize the molecular weight distribution of a polymer (which is what the "linear" columns are designed for) the results will be difficult to interpret, because the resulting calibration curve will no longer be linear.

If you are separating clearly different mw fractions, that may not be a problem.