Behavious of C8 columns

[N.V.V.S.S. RAMAN]

Hai

Recently I analysed a drug on Inertsil C8 250 x 4.6 mm and Targa C8 250x 4.6 mm. The compound is having two impurities which eluting at 24 min and 26 min on C8 are exactly eluting at 24 min and 26 min of Targa column but the order is changed.

The 24 min impurity on Inertsil C8 is eluting at 26 min on Targa C8
and 26 min impurity on Inertsil C8 is eluting at 24 min on Targa C8

There is no change in mobile phase, wavelength,
We simply removed the inertsil C8 and fixed Targa C8
And we conformed the change of impurities by spectrum of the compound as we analysed using PDA (using PDA is an advantage)

Can anybody explain about this abnormal behavious (as we can not claim an equalent column)

Raman

[Rob Burgess]

Is it just a case of different column "brands" showing different selctivities? This effect is not uncommon.

If you are trying to look for equivalent selectivity of columns of the various brands available, there is a graph somewhere that groups "similar" columns that should give similar selectivity and retention. Inertsil I believe is definitely on the graph (not sure about Targa, personally haven't heard of this packing material).

I can't recall where this information would be on the web but it is quite a well established graph and a good starting point to try and find "equivalent columns". Could someone provide a link please to this graph please?

[Srinivas SK]

Hello

Reversal of selectivity is quite possible, even with brands that are apparently equivalent. This depends on carbon load and end-capping efficiency, which can vary from brand to brand.

There's a simple way to cross-check - inject a mixture of benzene, toluene and xylene, about 0.1% dissolved in ACN and run it on both columns and see. Detection at 254 nm, flow rate 1 ml/min, mobile phase: ACN:water :: 80:20 ( or thereabouts). Average run time around 15 min.

Targa is a brand from Higgins Analytical, if I'm not mistaken.

Check out this link:

http://www.mac-mod.com/comparison_guide.html

It may be of use. I refer to this particular website quite often. Plenty of practical information.

[tom jupille]

You can also download a database of almost 300 commercial columns characterized for selectivity, along with a trial version of a spreadsheet which lets you evaluate the similarity/difference between columns:
http://www.rheodyne.com/products/chroma ... lumnmatch/

[Uwe Neue]

Actually, this raises an interesting question, and I would appreciate comments from the practitioners.

If I have two chromatographic methods that resolve all the peaks that I am interested in, what prevents me from saying that both methods are equivalent? Who cares what the elution order is, as long as all peaks are resolved and can be quantitated. Especially in the case described here, where even the same mobile phase is used. Both columns do the same job, and apparently equally well. So why would that mean that the two methods (or columns) are not equivalent?

[N.V.V.S.S. RAMAN]

Thank you

Yes the Targa is Higgins brand

And I am downloading the data (special thanks to Mr. S.K. Srinivas)

And Dear Neue
If we quantify the impurity against a reference stand, it won't give any difference. But if you identify and quantify using RRT anf RRF ur result will become wrong, and you qnatify one impurity against another impurity

Raman

[amaryl]

If we quantify the impurity against a reference stand, it won't give any difference. But if you identify and quantify using RRT anf RRF ur result will become wrong, and you qnatify one impurity against another impurity

Raman

How do you quantify your two impurities without some IS (internal standard.

Some formula?

Regards,

Amaryl.