By Mike LEVI on Wednesday, April 25, 2001 - 11:18 am:
Hi,
i'm trying to develop a qualification method for Hplc and i'd like to ask if you know some molecules which are quite apolar for a good retention on C18 and giving nice peak shape under Acetonitrile/water mobile phase.
Thanks,
Mike LEVI (french chromatographist, excuse my english!)
By tom jupille on Wednesday, April 25, 2001 - 11:58 am:
No excuse required, your English is better than my French. :-)
Benzene or toluene are often used for this purpose. I have also seen alkylphenones used (you can select a chain length to give you the retention you need).
-- Tom Jupille / LC Resources
By Anonymous on Thursday, April 26, 2001 - 08:47 am:
Depending on the retention you want, phthalate esters also give good peak shapes and you can purchase them from dimethyl through di-n-octyl. You can also get didodecyl phthalate if you really want retention!
By Kostas on Thursday, April 26, 2001 - 04:57 pm:
Why not use some already established test for reversed-phase columns? The advantage is that a lot of commercial columns have been already tested so you could compare if the performance of your "used" columns are the same with those of a new commercial column. Except from the hydrophobicity test there are some other tests (for residual silanol etc.). Maybe the most used test is the one of Tanaka and co-workers who uses the the selectivity factor (alfa) between the butyl benzene and amyl (pentyl) benzene to characterize the column hydrophobicity (mobile phase=70:30 MeOH-H2O). I'm not quite agree with this as in my opinion the methylene selectivity is not enough to say if a column more hydrophobic of another. However, a combination of the selectivity factor among the above compounds and the capacity factor of the amylbenzene together could give a better approach of the column hydrophobicity.
I think that you should include the residual silanol test as well (solutes: phenol and caffeine, mobile phase 20:80 water:methanol (for the mobile phase I'm not quite sure). Depending the elution order of this compounds you can get an idea of the residual silanols of the column. When caffeine is eluted before phenol you don't have much of residual silanols out there.
Below I cite some publications relative to column caracterization.
1.A proposal for a universal column quality certificate for HPLC columns. G. Wieland, K. Gabrera, W. Eymann. LC-GC Intl. (1998), February, 74-83.
2. Chromatographic classification of comercially available reverse-phase HPLC columns. E. Cruz, M. R. Euerby, C. M. Jonhson, C. A. Hackett. Chromatographia, (1997), 44 (3/4), 151-161.
3. A chromatogrphic test procedure for reversed-phase HPLC column eveluation. H. Engelhardt , M. Arangio, T. Lobert. LC-GC Intl. (1997), December, 803-809.
4. Chrommatographic characterization of silica C18 packing materials. Correlation between a preparation method and retention behavior of stationary phase. K. Kimata, K. Iwaguchi, S. Onishi, K. Jinno, R. Eksteen, K. Hosoya, M. Araki, N. Tanaka. J. Chromatogr. Sci. (1989), 27, December, 721-728.
Hope the above helps...
By simon on Saturday, February 28, 2004 - 01:03 am:
Can someone explain the difference between hydrophobicity measured by the capacity factor of two probes and hydrophobicity measured by methylene selectivity
By Anonymous on Saturday, February 28, 2004 - 07:21 pm:
Usually, one probe is used for measuring the hydrophobicity with the capacity factor. Often, toluene or ethylbenzene are used.
Methylene selectivity is the relative retention time of two such probes, for example ethylbenzene and toluene. I do not know why this is called hydrophobicity also. I think only the first one is hydrophobicity.
By simon on Sunday, February 29, 2004 - 02:38 am:
What factors affect hydrophobicity and what factors affects methylene selectivity
Posting is currently disabled in this topic. Contact your discussion moderator for more information.