Chromatography Forum

Hi all,

I'd like to collect folks' opinions on Hypercarb (graphite) columns. Specifically, if you've developed methods on them successfully, how you rate the technology versus derivatized silica or zirconium, what downsides you've seen, how reproducibly are they manufactured, how well they hold up to pressure, typical lifetimes, etc.

Opinions welcome!

Thanks,
Khimik

There have been extensive discussions on this.

28 posts in the archives:
http://www.google.com/search?ie=UTF-8&o ... ources.com

and 19 posts in the last year:
http://www.sepsci.com/chromforum/search ... de=results

In addition to everything that have been discussed, here are my brief opinion on this:

Do you like Hypercarb?: Yes, especially for it's alternative selectivities over C18. However, if I have the same separation with a simple C18 I would prefer the C18 due to the price tag etc...

Developed method on it? Yes I have, however you need to do some reading on it's retentin mechanisms

Rate of the technology over derviatized silica or zirconium. I prefer Hypercarb over Zirconium (although if you ask Prof. Carr you'll get a different response -he developed the zirconium...-). Again I would use the Hypercarb for whatever C18 can not do as easy...

Downsides: The efficiencies obtained are somehow lower than silica based ones. Also, you might get very frustrated results if you do not know what you are doing (i.e. splitted peaks etc...).

Manufacture reproducibility: It is quite challenging to manufacture them and they used to not be able to provide these column on time due to manufacturing difficulties (whole batches will go to the carbidge...). I do not think this is an issue any more.

Mechanical and chemical stability: Here Hypercarb excels with excellent pressure stabilities and you can easily use buffer of pH 0-14 with no problem. I would say that you can even leave the column at these extreme pH without flushing until the next use, although I never took the risk to test it...

Typical lifetimes: I found that they have the tendancy to get a little bit easier to junk them, probably due to higher affinities with some of the compunds (i.e. it is more hydrophobic than regular bonded silica and has very high affinities for planar molecules). Also they tend to retain negative charged molecules and for some of them you will need to increase the electronic competitors to get them out from there. THF is the solvent of choice for regenaration of Hypercarb (for hydrophobic compounds). High concentrations of acids are good to flush negative charged compounds...

Well... that was not brief at all!

Thanks Kostas for the detailed summary. Could you also say a few words about how method development is approached with these columns. Do you start with the same approach as for a C-18 column, except that...?

You may have covered it in the earlier threads, but would be good to mention briefly here.

Thanks Adam

It is an hydrophobic stationary phase so the method development is similar to the C18 but it depends... As I have mentioned in previous posts, we used Hypercarb in the past for analysis of inorganic anions, where the mechanisms involved are completly different. At that study for example we used perfluorinated carboxylic acids (and formic acid) as electronic competitors.... People have even applied a voltage to the column in order to manipulate selectivities and retention...

Also you might get some strange peak shapes if you are not in an appropriate pH (depending on your molecule) etc. I do not know the exact reasons, maybe if there are several mechanisms govering the retention at the same time you get unexpected results...

A small example of something unexpected (if you think in terms of silica C18 terms).

Mobile phase, water and TFA 0.1%, you inject aspartic acid it is eluted in void volume.
Mobile phase only water, you inject aspartic acid it never comes out.
Mobile phase water and gradient with ACN, you inject aspartic acid never comes out.
What happens in this example, Asp acid has a negative charge when only water was used as mobile phase, the column has an affinity for negative anions so you never see your hydrophylic molecule even with a gradient with ACN. You need to introduce either decrease the pH or maybe do a salt gradient...