Hybrid particles Technology: XBridge vs. Gemini

[SIELC_Tech]

I would like to get independent view from people who are using this new technology. We would like to conduct a comparison study between XBridge, Gemini and Primesep for the retention of basic, neutral, zwitter ionic compounds at various pH. We did a short study and now would like to extend it. From what I see in promotional fliers/ brochure both companies claim that one is much more stable than another with very convincing graphs, but if you put them side by side (brochures) you will be puzzled, because here is no correlation (I just looked at XBridge ad in American Laboratory and it shows fast decomposition of Gemini).
I would appreciate if people who tried XBridge and Gemini can share their results in terms of stability, retention control, robustness, etc.

Regards,


Vlad

[Mark Tracy]

Regrettably, there is no recognized standard for testing pH stability of columns. Vendors tend to use methods that put their product in a good light. The better ones give you enough detail that you can reproduce their test, but even then you need to read those details very closely.

[Koen Hollebekkers]

Like Mark mentioned, the discussion about column stability is not very unambiguous. I also have been involved in several column stability tests. Claessens recently published a orderly review article about the stability of various reversed phase supports.
If I look at the data given by several vendors, in some cases vendors show opposite information in there brochure as there competitor. I have to admit that the data of the X-bridge is looking very promising, whereas I have my doubts about the scientific background of the Phenomenex data. Also the data generated by Dionex looks realistic and they make a nice comparison, although there conditions at low pH are not harsh.
I just finished a study for the low pH stability of Pathfinder columns.
Since the column market is very dynamic (several new columns every year), and the stability of the new generation columns is increasing, it is difficult to set up a uniform testing protocol.
To compare the stability of columns from different vendors I reccomend:

---Low pH, like described by Iraneta in Journal of Chrom. 1 M TFA (100% aqueous) pH 1.0@ 85 degrees, with additional backpressure behind the column.

----High pH, 50 mMol TEA pH 10 @55 degrees.

These conditions are very aggressive and will make a clear discrimination between old columns and new types of supports.

[Rob Burgess]

Why can't column manufacturers look at column testing from the point of view of the end consumers?

For instance 50 mMol TEA gives high background absorbances and is virtually useless for impurity runs. Plus pH 10.0 isn't much use for many organic bases that have a pKa ca. 9 - 9.5.

That is why I have become interested in the X-bridge column. Reputedly it can run at pH 12 with a phosphate buffer. I'm hoping a phosphate buffer @ this pH will give us nice baselines for our 0.05% (i.e. very small) impurity peaks.

To us consumers the only way to tell if manufacturers claims our true is to test out the theory for your own particular application and then share the successes (on this board preferably) or ultimately draw (in)different conclusions about such claims!

[Uwe Neue]

Rob,

We do look at it from the users point as well. However, most of the data for stability comparisons (not only with competitors, but also with different prototype materials) are obtained under accelerated conditions. A stability test over the useful pH range of a packing under useful conditions may take long months to accomplish. A few years ago, I did one for XTerra, therefore I know what I am talking about...

[Ary]

There are two sides to this story. 1 the end user would like to be able to pick up data sheets on every column and have a set of criteria to compare. 2 the manufacturers want to promote their products in the best possible light. However even if someone or some oragnisational body could come up with a set of tests and all of the manufacturers could be persuaded to run the tests and publish the results it only gives an indication of potential. Ultimately every application is subtly different and the results from a standard test do not necessarily give an answer to how a column may perform in a "real" situation. Therefore there is less incentive for a manufacturer to follow a set protocol which may show their product in a poor light. So its usually a case of suck it and see. As an example I've been running a system using an Xterra column but getting around 30 injections before I destroy the column. Talking with the rep and with the kind help of Uwe I was convinced switching to Xbridge would give me an increase in column lifetimes without any major impact on my chromatography. So much for theory, I get almost zero retention of any compound. Yet I know of other users who get significantly better results its just my bad luck it doesnt seem to work in my case. Does this mean this column is rubbish? I definitely dont think so but would Waters have wanted to use the conditions I do and then publish the results? I doubt it and I doubt if any of the other manufacturers would either. Anyway for what its worth thats my opinion folks.

[HW Mueller]

If things were less proprietary we could probably figure out what stability to expect.

[Uwe Neue]

Ary, please contact me at my private e-mail address Uwe.Neue@Prodigy.net. I am very surprised that you get no retention on XBridge while good retention on XTerra. The phase ratios of both packings are so similar that I find it very difficult to understand.

[Uwe Neue]

One more comment, especially to the comment by Mark.

Once we have established a method for the accelerated stability testing of columns, we do not only use it for our own packings and prototypes, we also use the exact same method for testing competitive columns that we purchase. Thus for our methods you will usually find a long list of columns that have been tested under the exact same conditions. This permits a true comparison.

To Rob:

I recognize that a test with 1M TFA at 85 degrees probably means nothing to the user. However, I do believe that this translates in a very straightforward way to the stability of the same packings in 20 mM TFA at room temperature. The idea here is the same as the accelerated testing done in the pharmaceutical industry.

[SIELC_Tech]

I put stability testing for Gemini, XBridge and XTerra side by side and try to solve an equation: According to Waters:
XBridge is more stable then XTerra and XTerra is more stable then Gemini.

According to Phenomenex Gemini is more stable then XTerra. This contradicts Waters studies. Comparisons are made at pH 11.5 (waters) and pH-10 (Phenomenex). So which one is more stable? Is XTerra more stable at 11.5 then at 10? How valid are this data. You would expect some correlation between two studies if both of them are accurate.
Trying to reproduce stability testing and retention patterns and compare these two to our columns, although we in no way claiming stability at pH 10-11.5. We just trying to see why there is a need to go to such extremes to retain basic compounds?

Regards,

Vlad