Chromatography Forum

I need to purchase a new organic acid column. I've used such from both Grace/Alltech (Prevail OAC) and Restek (Allure OAC). Neither's Tech Help was very helpful how to rinse the column to prolong column life post-analysis, said these OA columns were different than typical columns, but the column came with instructions for typical columns.

My peak shapes are getting worse over time, like for citric acid. I'm also doing other organic acids in the same injection but am not able to disclose those identities right now.

So maybe someone here like the Consumer Products Guy or someone else could help out; I'm thinking about flushing with methanol immediately after samples complete. I use a mobile phase of 0.002 to 0.003 sulfuric acid and conductivity detector.

Thanks.

If you are looking for small molecular organic acids like citrate, anion exchange columns would be a good idea e.g. IonPac AS11-HC. This column can separate about 44 different anions in 50 minutes.

http://www.dionex.com/en-us/products/co ... 11520.html

http://www.bio-rad.com/de-de/product/am ... is-columns or similar, comparable columns are mostly used and you will find a lot of technical support of such web sites. Flushing with water would be a good idea. What matrix your samples are from?

Those columns are PS-DVB sulfonate cation exchange resins in the H+ form. Typically used with a dilute acid mobile phase (e.g., sulfuric acid). They are generally quite robust but they do not take kindly to samples which contain heavy metals or even NaCl. Cations in the sample can build up on the columm by displacing the H+. Rinsing with a higher concentration of acid can get rid of Na+, but it can take a long time. If your samples contain high levels of salt, better to use a guard cartridge and change it periodically.

Whatever you do, do NOT flush such a column with methanol. Depending on the crosslinkage and degree of sulfonation, methanol can catastrophically shrink the resin beads and disrupt the integrity of the packing bed.

I'll double Farooq, Get your self an anion exchanger.
Or go for HILC.

Best Regards

I've E-mailed the column supplier for specific advice.

We don't have resources these days (love the cost-cutting mentality) to investigate alternative columns, so just looking to increase column life and number of injections. So no time to look into SPE to remove potential interferences/contaminants, but since we use 100% aqueous mobile phase, possibly even an RP-18 guard cartridge could retain nonionic organic stuff.

Whatever you do, do NOT flush such a column with methanol. Depending on the crosslinkage and degree of sulfonation, methanol can catastrophically shrink the resin beads and disrupt the integrity of the packing bed.

Tom - Restek uses 85% methanol and 15% water in its check-out/reference chromatograms for these Allure organic acid columns. We have two such columns, and that MP was used for both check-outs.

I've E-mailed the column supplier for specific advice.

Restek Tech Help responded, gal asked another Tech for advice. Here's the consensus:
post-Sequence, rinse out with water, then rinse with acetonitrile for storage between uses.

Restek also recommends the guard cartridge, which I had surmised.

Restek uses 85% methanol and 15% water in its check-out/reference chromatograms for these Allure organic acid columns.

. I had assumed they were resin-based ion-exclusion columns, but I just looked them up and they *are* silica based. That's what I get for jumping to confusions

All I can add is that we've used organic acid columns and ion-exclusion columns for these. Which works better? I'd say it depends on the sample matrix itself.

Dear all

There are several wrong/misunderstanding answers given. Let me clarify:

1) The IonPac AS11-HC is an anion exchanger column and normally used with hydroxide eluent in combination with suppressed conductivity detection. However it can also be used with acidic eluent and and UV-detection. But this column is fully compatible with organic eluents such as MeOH or ACN.. Additionally the AS11-HC (and more or less all IonPac columns) are polymere DVB PS based and not silica based columns.
2) Weak cation exchanger are NOT compatible with MeOH or alcohols in general. The carbonic exchange group will form esters.
Strong cation exchanger normally contains sulfonic groups and they are compatible with MeOH.
3) There is a silica based column for organic acids available from ThermoFisher (form. Dionex): You can find details here: http://www.dionex.com/en-us/products/co ... 71770.html
4) Or, as already mentioned, try HILIC/Mixed Mode columns: http://www.dionex.com/en-us/products/co ... 71737.html

Good luck!

Strong cation exchanger normally contains sulfonic groups and they are compatible with MeOH.

The sulfonate group is compatible with methanol, but many sulfonated PS-DVB resins are not. It has nothing to do with the chemistry of the sulfonate group and everything to do with osmotic shrinking/swelling of the resin. Note the compatibilities given by Bio-Rad for their columns:
http://www.bio-rad.com/webroot/web/pdf/ ... LIT42D.PDF

How many injections you get on your column?
One thing to increase life time of such a column is to avoid too harsh pressure peaks. So be careful when you switch on your pump.
If you have fat from the matrix in your sample just put it into the freezer for a while and filter and/or centrifuge the sample. That will also increase the life time of your column. Good luck.

I assayed our prototype product using the existing organic acid column, and it looked acceptable.

So I purchased a new organic acid column and guard cartridges, and supplier said to wash post-sequence with water, then water-ACN after that in between uses. I don't know if I'll have time to explore removing neutral organics before they hit the column itself, like SPE or RP-18 guard cartridge, too many higher priority projects (EVERYTHING here is #1 priority!).

It's a living.