Incompatible guard column

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Hi...

I got a problem with installation of new HPLC. According to the column supplier, we just need the analytical column and guard cartridge (in fact, the guard cartridge needs holder). So the situation now is, we have HPLC, analytical column and guard cartridge but still have to wait another weeks for the shipment of holder.
We need to operate the HPLC as soon as possible and there is an idea of using temporary guard column. The analytical column is carbohydrate analysis column (separation based on combination of size exclusion and ligand exchange). Not sure with the temporary guard column but definitely it is a different type with the analytical one. Is there any consequences of this kind of practice?
Thank you
Hi 88TSodium

In my experience the guard column is a solution for a non existent problem. If you filter your mobile phases I think you did not need the guard column. Many years ago I tried them and finding exactly the same phases for both of them was a problem. I'll start working inmediately.

Good luck

Fernando
(1) How useful is a guard column with different chemistry to the analytical column? The answer depends on how different. A very different guard will be a poor guard and may mess up your method. A very similar guard might be a bit helpful. Any guard will act as an inline filter if you have particulate contamination in your samples.

(2) How essential are guard columns in general? It depends entirely on your method and samples. If you run dirty samples that tend to bind to a column irreversibly, then a guard column can save you a lot of expense. If you run clean standards that elute well, then it is probably unnecessary. For clean samples that are well-prepared, it's possible it's unnecessary. I would add that in some situations a guard column is cheaper than filtering. For example, if you run very small volume samples and use spin-filters, then these probably cost about 1/30th of the price of a guard cartridge, so unless you block the guard in less than 30 runs, it's cheaper to use the guard instead of the spin-filters! In consequence, for simple C18 stuff I now use a guard, centrifuge almost every sample, but filter nothing (OK, actually I probably filter a sample once or twice a year, if I get one that is obviously very particulate and will not sediment).
As lmh pointed out, the guard column does more than just filtering (in fact, if particulates are the problem, a guard column is an expensive way to go). The more important function is to trap compounds which would otherwise strongly bind to your analytical column (that's why it's usually packed with the same material as the analytical column). Depending the ionic form of your column, this might include sodium or heavy metal cations.

If you're confident that your sample don't contain anything that will kill your column, I would go ahead and run without the guard.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
The temporary guard is C18 and the ionic form of my column is Ca (column is sulfonated divinyl benzene-styrene copolymer with calcium ionic form).
In this case, will any ionic content of sample affect/damage the column?
I would not bother with a C18 guard cartridge. Ca++ is fairly tightly bound, but high concentrations of Na+ in the sample can still displace some of it. Iron, zinc, copper would also be strongly bound.

Unless your samples have a very high salt content, I wouldn't worry too much about it. How many samples are you likely to run?
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Around 100 samples.
The samples will be filtered and treated with ion exchange resin before it goes to HPLC. Hopefully it is quite safe to be run without guard column.
I'm going to agree with a lot of what the others said here.

Guard columns have never been shown to be anything more than a nuisance in my history of LC. If your sample prep is adequate, then there's no reason to use one. Especially since the guard you're using (C18) will trap nothing useful in regards to cation/anion exchange.
I really wouldn't write off guard-columns as a universally bad idea. Of course it's possible to prepare samples so cleanly that they will never harm an analytical column, and that is certainly good sample prep, but it takes time, which is a limited commodity! Often it's possible to get fine results from really quite unpleasantly dirty samples, but with the disadvantage that back pressure creeps up and retention times start to move after a few hundred injections. If using, and changing a guard solves the problem, then it's worth considering.

To take a concrete example, Luna guard cartridges in the UK currently cost about £200 for a pack of 10, I think. It takes me about 5 minutes to find and change a Luna guard, so if I decide to change a Luna guard every 250 samples, my cost per sample is 0.08 pounds, and the time spent per sample is just over a second. If, instead, I decide to put the samples through microcentrifuge spin-filters, these cost about 1 pound per sample, and if I spin them in batches of 18 (the size of my centrifuge) and pipette them, I'm probably going to do 20 seconds work on each sample. Of course syringe-tip filters are cheaper if you have enough sample, but they're even more time-consuming to handle, not to mention the added plastic waste.

In many cases an inline filter would do just as well as a guard, of course. Removing highly-retained stuff by SPE is going to add a lot of time and expense to the sample prep, and it's something I would avoid unless the SPE gives me better results or allows me to concentrate up an unreasonably dilute sample.
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