Size Exclusion Column for Polar Polymers

Discussions about gel permeation chromatography / gel filtration chromatography / size exclusion chromatography

7 posts Page 1 of 1
Hello

We are currently looking for a good SEC column for analysis of polar polymers (things like polyethylene glycol, pemulen, hydroxyethyl cellulose).

Can anyone recommend any goo brands or types of columns. We don't care so much about speed. What is more important is ruggedness, low bleed so you can use with ELSD, and one column that can be used for many applications.

Jordi offers some columns that are claimed to offer all of these things. Anyone have any experience with their columns. Or Shodex, Tosoh, etc.

Any suggestions are appreciated.
You already mentioned the actual most common SEC column manufacturers.
Looking on the product specifications and applications on these websites are helpful.
I'm sure Andy Alpert from PolyLC can tell you more specificly what column is best.
Good luck
Gerhard Kratz, Kratz_Gerhard@web.de
You aren't going to get a fast analysis in any case. Optimal separation in the SEC mode is obtained at flow rates about 8x slower than would be used for a column the same size in a gradient mode. This is necessary to insure that the smallest analytes have time to diffuse to the bottom of the pores, thereby accentuating the difference in column volume available to them vs. a larger analyte. That's why SEC columns tend to be large; you can elute them at flow rates that most HPLC systems can deliver reliably.

The next factor you should be concerned with is the pore volume. The greater the pore volume, the wider the separation of analytes within the fractionation range. Generally, silica-based materials can be made with greater pore volume than can polymeric materials, which require thicker walls between the pores in order to withstand the backpressure of HPLC. The Jordi materials are the most durable in this category, as far as I know. That said, I advise you to compare their pore volume with that of good silica-based materials. There's no point in getting a column that lasts forever if it can't separate your analytes well enough. Tosoh's polar silica-based materials for SEC perform well overall. However, their good separation within the fractionation range comes at the expense of durability; the pore volume seems to have been increased by making the walls between the pores thinner. We've gotten reports of these SEC columns failing after 3-4 weeks of use. An example of a compromise would be our PolyHYDROXYETHYL A columns. The pore volume is certainly smaller than that of the Tosoh silica and so the separation isn't as good within the fractionation range that you're interested in. However, if the results are good enough nonetheless, then you'll have a column that performs well enough for a reasonable period of time.

I might mention that a number of polymers have to be separated in SEC using organic solvents; an example is the use of hexafluoro-2-propanol as the solvent for analysis of nylon. In such cases, there's no substitute for a rugged material like Jordi's. In your case, though, gentle aqueous solvents would work fine. Any intramolecular interactions can be suppressed by including a small amount of a chaotrope in the mobile phase.
PolyLC Inc.
(410) 992-5400
aalpert@polylc.com
Andy - Thanks for your response.

Let me ask: are you referring to Tosoh's Super MultiPore Columns, in terms of being not rugged (this is the one we were thinking about).

Also, let me ask something else: Some folks have suggested that silica columns don't work as well for polymers. Not obvious to me why that should be other than some acidity from the Silanols. Any thoughts...?

Thanks Again.
Adam
Oh and I should also mention that we will be using a Charged Aerosol Detector for all of our work. So we want to minimize use of non-volatile salts.

This requirement alone perhaps suggests that we should use a polymeric packing rather than a silica based packing; as polymeric packings have less of a requirement for salt in the mobile phase and bleed less.

Any comments are appreciated.

Thanks!!
My personal rule of thumb is to use a polymeric sorbent for analysing polymers by SEC and a silica sorbent for other types of molecule (peptides, proteins etc.).
Mixed bed columns provide a reasonable compromise for a wide range of molecular weights, however you will probably need to run at least two columns in series to give good resolution. Thankfully the slow flow rates needed mean that back pressures shouldn't be excessive.
Silica columns do tend to need a fair amount of buffer/salt present to overcome non-specific interactions.
Adam -

Tosoh is a competitor of ours and we don't systematically assess their products. My information concerned only the columns with a single pore diameter that are used for protein SEC. I have no idea about the performance of their Multipore columns.

Coffo's comments are correct; silica-based materials manifest charges and so some electrolyte should be included in the mobile phase if the analytes have any charge. If they don't, then it may not be necessary. You can certainly use a volatile electrolyte such as dilute formic acid if you want to use ELSD or MS detection. However, unbuffered acids are mild chaotropes and so will shift the fractionation range compared with what you will get using a buffered salt as the additive. Here's a link to my book chapter on the subject: http://www.polylc.com/downloads/SEC_boo ... r_ver1.pdf
The effect is on the stationary phase, since you'll see the same effect with solutes that are too small to have any tertiary or secondary structure to denature. Any SEC material that does not exhibit this effect probably has a coating that's so thin that the chromatography material will not be well-hydrated. That could be a problem with the polar polymers that you want to analyze; there could be some hydrophobic interaction.
PolyLC Inc.

(410) 992-5400

aalpert@polylc.com
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